Revision: 1130
http://www.exim.org/viewvc/pcre2?view=rev&revision=1130
Author: ph10
Date: 2019-07-13 12:12:03 +0100 (Sat, 13 Jul 2019)
Log Message:
-----------
Implement non-atomic positive assertions.
Modified Paths:
--------------
code/trunk/ChangeLog
code/trunk/HACKING
code/trunk/doc/html/pcre2compat.html
code/trunk/doc/html/pcre2pattern.html
code/trunk/doc/html/pcre2syntax.html
code/trunk/doc/pcre2.txt
code/trunk/doc/pcre2compat.3
code/trunk/doc/pcre2pattern.3
code/trunk/doc/pcre2syntax.3
code/trunk/src/pcre2.h.in
code/trunk/src/pcre2_auto_possess.c
code/trunk/src/pcre2_compile.c
code/trunk/src/pcre2_dfa_match.c
code/trunk/src/pcre2_error.c
code/trunk/src/pcre2_internal.h
code/trunk/src/pcre2_match.c
code/trunk/src/pcre2_printint.c
code/trunk/src/pcre2_study.c
code/trunk/testdata/testinput2
code/trunk/testdata/testoutput2
code/trunk/testdata/testoutput5
Modified: code/trunk/ChangeLog
===================================================================
--- code/trunk/ChangeLog 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/ChangeLog 2019-07-13 11:12:03 UTC (rev 1130)
@@ -88,7 +88,9 @@
17. Check for integer overflow when computing lookbehind lengths. Fixes
Clusterfuzz issue 15636.
+18. Implement non-atomic positive lookaround assertions.
+
Version 10.33 16-April-2019
---------------------------
Modified: code/trunk/HACKING
===================================================================
--- code/trunk/HACKING 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/HACKING 2019-07-13 11:12:03 UTC (rev 1130)
@@ -195,6 +195,7 @@
META_FAIL (*FAIL)
META_KET ) closing parenthesis
META_LOOKAHEAD (?= start of lookahead
+META_LOOKAHEAD_NA (*napla: start of non-atomic lookahead
META_LOOKAHEADNOT (?! start of negative lookahead
META_NOCAPTURE (?: no capture parens
META_PLUS +
@@ -286,8 +287,9 @@
of the main word contain the length of the first branch of the lookbehind
group; this is used when generating OP_REVERSE for that branch.
-META_LOOKBEHIND (?<=
-META_LOOKBEHINDNOT (?<!
+META_LOOKBEHIND (?<= start of lookbehind
+META_LOOKBEHIND_NA (*naplb: start of non-atomic lookbehind
+META_LOOKBEHINDNOT (?<! start of negative lookbehind
The following are followed by two elements, the minimum and maximum. Repeat
values are limited to 65535 (MAX_REPEAT). A maximum value of "unlimited" is
@@ -715,13 +717,15 @@
----------
Forward assertions are also just like other subpatterns, but starting with one
-of the opcodes OP_ASSERT or OP_ASSERT_NOT. Backward assertions use the opcodes
-OP_ASSERTBACK and OP_ASSERTBACK_NOT, and the first opcode inside the assertion
-is OP_REVERSE, followed by a count of the number of characters to move back the
-pointer in the subject string. In ASCII or UTF-32 mode, the count is also the
-number of code units, but in UTF-8/16 mode each character may occupy more than
-one code unit. A separate count is present in each alternative of a lookbehind
-assertion, allowing them to have different (but fixed) lengths.
+of the opcodes OP_ASSERT, OP_ASSERT_NA (non-atomic assertion), or
+OP_ASSERT_NOT. Backward assertions use the opcodes OP_ASSERTBACK,
+OP_ASSERTBACK_NA, and OP_ASSERTBACK_NOT, and the first opcode inside the
+assertion is OP_REVERSE, followed by a count of the number of characters to
+move back the pointer in the subject string. In ASCII or UTF-32 mode, the count
+is also the number of code units, but in UTF-8/16 mode each character may
+occupy more than one code unit. A separate count is present in each alternative
+of a lookbehind assertion, allowing each branch to have a different (but fixed)
+length.
Conditional subpatterns
@@ -754,11 +758,11 @@
or OP_FALSE.
If a condition is not a back reference, recursion test, DEFINE, or VERSION, it
-must start with a parenthesized assertion, whose opcode normally immediately
-follows OP_COND or OP_SCOND. However, if automatic callouts are enabled, a
-callout is inserted immediately before the assertion. It is also possible to
-insert a manual callout at this point. Only assertion conditions may have
-callouts preceding the condition.
+must start with a parenthesized atomic assertion, whose opcode normally
+immediately follows OP_COND or OP_SCOND. However, if automatic callouts are
+enabled, a callout is inserted immediately before the assertion. It is also
+possible to insert a manual callout at this point. Only assertion conditions
+may have callouts preceding the condition.
A condition that is the negative assertion (?!) is optimized to OP_FAIL in all
parts of the pattern, so this is another opcode that may appear as a condition.
@@ -823,4 +827,4 @@
opcode are the correct length, in order to catch updating errors.
Philip Hazel
-20 July 2018
+12 July 2019
Modified: code/trunk/doc/html/pcre2compat.html
===================================================================
--- code/trunk/doc/html/pcre2compat.html 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/doc/html/pcre2compat.html 2019-07-13 11:12:03 UTC (rev 1130)
@@ -205,6 +205,11 @@
(l) PCRE2 recognizes some special sequences such as (*CR) or (*NO_JIT) at
the start of a pattern that set overall options that cannot be changed within
the pattern.
+<br>
+<br>
+(m) PCRE2 supports non-atomic positive lookaround assertions. This is an
+extension to the lookaround facilities. The default, Perl-compatible
+lookarounds are atomic.
</P>
<P>
18. The Perl /a modifier restricts /d numbers to pure ascii, and the /aa
@@ -234,7 +239,7 @@
REVISION
</b><br>
<P>
-Last updated: 12 February 2019
+Last updated: 13 July 2019
<br>
Copyright © 1997-2019 University of Cambridge.
<br>
Modified: code/trunk/doc/html/pcre2pattern.html
===================================================================
--- code/trunk/doc/html/pcre2pattern.html 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/doc/html/pcre2pattern.html 2019-07-13 11:12:03 UTC (rev 1130)
@@ -33,17 +33,18 @@
<li><a name="TOC18" href="#SEC18">ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS</a>
<li><a name="TOC19" href="#SEC19">BACKREFERENCES</a>
<li><a name="TOC20" href="#SEC20">ASSERTIONS</a>
-<li><a name="TOC21" href="#SEC21">SCRIPT RUNS</a>
-<li><a name="TOC22" href="#SEC22">CONDITIONAL GROUPS</a>
-<li><a name="TOC23" href="#SEC23">COMMENTS</a>
-<li><a name="TOC24" href="#SEC24">RECURSIVE PATTERNS</a>
-<li><a name="TOC25" href="#SEC25">GROUPS AS SUBROUTINES</a>
-<li><a name="TOC26" href="#SEC26">ONIGURUMA SUBROUTINE SYNTAX</a>
-<li><a name="TOC27" href="#SEC27">CALLOUTS</a>
-<li><a name="TOC28" href="#SEC28">BACKTRACKING CONTROL</a>
-<li><a name="TOC29" href="#SEC29">SEE ALSO</a>
-<li><a name="TOC30" href="#SEC30">AUTHOR</a>
-<li><a name="TOC31" href="#SEC31">REVISION</a>
+<li><a name="TOC21" href="#SEC21">NON-ATOMIC ASSERTIONS</a>
+<li><a name="TOC22" href="#SEC22">SCRIPT RUNS</a>
+<li><a name="TOC23" href="#SEC23">CONDITIONAL GROUPS</a>
+<li><a name="TOC24" href="#SEC24">COMMENTS</a>
+<li><a name="TOC25" href="#SEC25">RECURSIVE PATTERNS</a>
+<li><a name="TOC26" href="#SEC26">GROUPS AS SUBROUTINES</a>
+<li><a name="TOC27" href="#SEC27">ONIGURUMA SUBROUTINE SYNTAX</a>
+<li><a name="TOC28" href="#SEC28">CALLOUTS</a>
+<li><a name="TOC29" href="#SEC29">BACKTRACKING CONTROL</a>
+<li><a name="TOC30" href="#SEC30">SEE ALSO</a>
+<li><a name="TOC31" href="#SEC31">AUTHOR</a>
+<li><a name="TOC32" href="#SEC32">REVISION</a>
</ul>
<br><a name="SEC1" href="#TOC1">PCRE2 REGULAR EXPRESSION DETAILS</a><br>
<P>
@@ -2364,19 +2365,23 @@
match for the assertion to be true) or negative (must not match for the
assertion to be true). An assertion group is matched in the normal way,
and if it is true, matching continues after it, but with the matching position
-in the subject string is was it was before the assertion was processed.
+in the subject string reset to what it was before the assertion was processed.
</P>
<P>
-A lookaround assertion may also appear as the condition in a
+The Perl-compatible lookaround assertions are atomic. If an assertion is true,
+but there is a subsequent matching failure, there is no backtracking into the
+assertion. However, there are some cases where non-atomic assertions can be
+useful. PCRE2 has some support for these, described in the section entitled
+<a href="#nonatomicassertions">"Non-atomic assertions"</a>
+below, but they are not Perl-compatible.
+</P>
+<P>
+A lookaround assertion may appear as the condition in a
<a href="#conditions">conditional group</a>
(see below). In this case, the result of matching the assertion determines
which branch of the condition is followed.
</P>
<P>
-Lookaround assertions are atomic. If an assertion is true, but there is a
-subsequent matching failure, there is no backtracking into the assertion.
-</P>
-<P>
Assertion groups are not capture groups. If an assertion contains capture
groups within it, these are counted for the purposes of numbering the capture
groups in the whole pattern. Within each branch of an assertion, locally
@@ -2429,11 +2434,11 @@
Alphabetic assertion names
</b><br>
<P>
-Traditionally, symbolic sequences such as (?= and (?<= have been used to specify
-lookaround assertions. Perl 5.28 introduced some experimental alphabetic
-alternatives which might be easier to remember. They all start with (* instead
-of (? and must be written using lower case letters. PCRE2 supports the
-following synonyms:
+Traditionally, symbolic sequences such as (?= and (?<= have been used to
+specify lookaround assertions. Perl 5.28 introduced some experimental
+alphabetic alternatives which might be easier to remember. They all start with
+(* instead of (? and must be written using lower case letters. PCRE2 supports
+the following synonyms:
<pre>
(*positive_lookahead: or (*pla: is the same as (?=
(*negative_lookahead: or (*nla: is the same as (?!
@@ -2606,9 +2611,64 @@
</pre>
is another pattern that matches "foo" preceded by three digits and any three
characters that are not "999".
+<a name="nonatomicassertions"></a></P>
+<br><a name="SEC21" href="#TOC1">NON-ATOMIC ASSERTIONS</a><br>
+<P>
+The traditional Perl-compatible lookaround assertions are atomic. That is, if
+an assertion is true, but there is a subsequent matching failure, there is no
+backtracking into the assertion. However, there are some cases where non-atomic
+positive assertions can be useful. PCRE2 provides these using the following
+syntax:
+<pre>
+ (*non_atomic_positive_lookahead: or (*napla:
+ (*non_atomic_positive_lookbehind: or (*naplb:
+</pre>
+Consider the problem of finding the right-most word in a string that also
+appears earlier in the string, that is, it must appear at least twice in total.
+This pattern returns the required result as captured substring 1:
+<pre>
+ ^(?x)(*napla: .* \b(\w++)) (?> .*? \b\1\b ){2}
+</pre>
+For a subject such as "word1 word2 word3 word2 word3 word4" the result is
+"word3". How does it work? At the start, ^(?x) anchors the pattern and sets the
+"x" option, which causes white space (introduced for readability) to be
+ignored. Inside the assertion, the greedy .* at first consumes the entire
+string, but then has to backtrack until the rest of the assertion can match a
+word, which is captured by group 1. In other words, when the assertion first
+succeeds, it captures the right-most word in the string.
</P>
-<br><a name="SEC21" href="#TOC1">SCRIPT RUNS</a><br>
<P>
+The current matching point is then reset to the start of the subject, and the
+rest of the pattern match checks for two occurrences of the captured word,
+using an ungreedy .*? to scan from the left. If this succeeds, we are done, but
+if the last word in the string does not occur twice, this part of the pattern
+fails. If a traditional atomic lookhead (?= or (*pla: had been used, the
+assertion could not be re-entered, and the whole match would fail. The pattern
+would succeed only if the very last word in the subject was found twice.
+</P>
+<P>
+Using a non-atomic lookahead, however, means that when the last word does not
+occur twice in the string, the lookahead can backtrack and find the second-last
+word, and so on, until either the match succeeds, or all words have been
+tested.
+</P>
+<P>
+Two conditions must be met for a non-atomic assertion to be useful: the
+contents of one or more capturing groups must change after a backtrack into the
+assertion, and there must be a backreference to a changed group later in the
+pattern. If this is not the case, the rest of the pattern match fails exactly
+as before because nothing has changed, so using a non-atomic assertion just
+wastes resources.
+</P>
+<P>
+Non-atomic assertions are not supported by the alternative matching function
+<b>pcre2_dfa_match()</b>. They are also not supported by JIT (but may be in
+future). Note that assertions that appear as conditions for
+<a href="#conditions">conditional groups</a>
+(see below) must be atomic.
+</P>
+<br><a name="SEC22" href="#TOC1">SCRIPT RUNS</a><br>
+<P>
In concept, a script run is a sequence of characters that are all from the same
Unicode script such as Latin or Greek. However, because some scripts are
commonly used together, and because some diacritical and other marks are used
@@ -2669,7 +2729,7 @@
should not be used within a script run group, because it causes an immediate
exit from the group, bypassing the script run checking.
<a name="conditions"></a></P>
-<br><a name="SEC22" href="#TOC1">CONDITIONAL GROUPS</a><br>
+<br><a name="SEC23" href="#TOC1">CONDITIONAL GROUPS</a><br>
<P>
It is possible to cause the matching process to obey a pattern fragment
conditionally or to choose between two alternative fragments, depending on
@@ -2845,8 +2905,13 @@
<P>
If the condition is not in any of the above formats, it must be a parenthesized
assertion. This may be a positive or negative lookahead or lookbehind
-assertion. Consider this pattern, again containing non-significant white space,
-and with the two alternatives on the second line:
+assertion. However, it must be a traditional atomic assertion, not one of the
+PCRE2-specific
+<a href="#nonatomicassertions">non-atomic assertions.</a>
+</P>
+<P>
+Consider this pattern, again containing non-significant white space, and with
+the two alternatives on the second line:
<pre>
(?(?=[^a-z]*[a-z])
\d{2}-[a-z]{3}-\d{2} | \d{2}-\d{2}-\d{2} )
@@ -2865,7 +2930,7 @@
assertion, whether it succeeds or fails. (Compare non-conditional assertions,
for which captures are retained only for positive assertions that succeed.)
<a name="comments"></a></P>
-<br><a name="SEC23" href="#TOC1">COMMENTS</a><br>
+<br><a name="SEC24" href="#TOC1">COMMENTS</a><br>
<P>
There are two ways of including comments in patterns that are processed by
PCRE2. In both cases, the start of the comment must not be in a character
@@ -2895,7 +2960,7 @@
it does not terminate the comment. Only an actual character with the code value
0x0a (the default newline) does so.
<a name="recursion"></a></P>
-<br><a name="SEC24" href="#TOC1">RECURSIVE PATTERNS</a><br>
+<br><a name="SEC25" href="#TOC1">RECURSIVE PATTERNS</a><br>
<P>
Consider the problem of matching a string in parentheses, allowing for
unlimited nested parentheses. Without the use of recursion, the best that can
@@ -3083,7 +3148,7 @@
"b" and so the whole match succeeds. This match used to fail in Perl, but in
later versions (I tried 5.024) it now works.
<a name="groupsassubroutines"></a></P>
-<br><a name="SEC25" href="#TOC1">GROUPS AS SUBROUTINES</a><br>
+<br><a name="SEC26" href="#TOC1">GROUPS AS SUBROUTINES</a><br>
<P>
If the syntax for a recursive group call (either by number or by name) is used
outside the parentheses to which it refers, it operates a bit like a subroutine
@@ -3131,7 +3196,7 @@
<a href="#btsub">"Backtracking verbs in subroutines"</a>
below.
<a name="onigurumasubroutines"></a></P>
-<br><a name="SEC26" href="#TOC1">ONIGURUMA SUBROUTINE SYNTAX</a><br>
+<br><a name="SEC27" href="#TOC1">ONIGURUMA SUBROUTINE SYNTAX</a><br>
<P>
For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or
a number enclosed either in angle brackets or single quotes, is an alternative
@@ -3149,7 +3214,7 @@
Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are <i>not</i>
synonymous. The former is a backreference; the latter is a subroutine call.
</P>
-<br><a name="SEC27" href="#TOC1">CALLOUTS</a><br>
+<br><a name="SEC28" href="#TOC1">CALLOUTS</a><br>
<P>
Perl has a feature whereby using the sequence (?{...}) causes arbitrary Perl
code to be obeyed in the middle of matching a regular expression. This makes it
@@ -3225,7 +3290,7 @@
</pre>
The doubling is removed before the string is passed to the callout function.
<a name="backtrackcontrol"></a></P>
-<br><a name="SEC28" href="#TOC1">BACKTRACKING CONTROL</a><br>
+<br><a name="SEC29" href="#TOC1">BACKTRACKING CONTROL</a><br>
<P>
There are a number of special "Backtracking Control Verbs" (to use Perl's
terminology) that modify the behaviour of backtracking during matching. They
@@ -3739,12 +3804,12 @@
is no such group within the subroutine's group, the subroutine match fails and
there is a backtrack at the outer level.
</P>
-<br><a name="SEC29" href="#TOC1">SEE ALSO</a><br>
+<br><a name="SEC30" href="#TOC1">SEE ALSO</a><br>
<P>
<b>pcre2api</b>(3), <b>pcre2callout</b>(3), <b>pcre2matching</b>(3),
<b>pcre2syntax</b>(3), <b>pcre2</b>(3).
</P>
-<br><a name="SEC30" href="#TOC1">AUTHOR</a><br>
+<br><a name="SEC31" href="#TOC1">AUTHOR</a><br>
<P>
Philip Hazel
<br>
@@ -3753,9 +3818,9 @@
Cambridge, England.
<br>
</P>
-<br><a name="SEC31" href="#TOC1">REVISION</a><br>
+<br><a name="SEC32" href="#TOC1">REVISION</a><br>
<P>
-Last updated: 22 June 2019
+Last updated: 13 July 2019
<br>
Copyright © 1997-2019 University of Cambridge.
<br>
Modified: code/trunk/doc/html/pcre2syntax.html
===================================================================
--- code/trunk/doc/html/pcre2syntax.html 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/doc/html/pcre2syntax.html 2019-07-13 11:12:03 UTC (rev 1130)
@@ -32,15 +32,16 @@
<li><a name="TOC17" href="#SEC17">NEWLINE CONVENTION</a>
<li><a name="TOC18" href="#SEC18">WHAT \R MATCHES</a>
<li><a name="TOC19" href="#SEC19">LOOKAHEAD AND LOOKBEHIND ASSERTIONS</a>
-<li><a name="TOC20" href="#SEC20">SCRIPT RUNS</a>
-<li><a name="TOC21" href="#SEC21">BACKREFERENCES</a>
-<li><a name="TOC22" href="#SEC22">SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)</a>
-<li><a name="TOC23" href="#SEC23">CONDITIONAL PATTERNS</a>
-<li><a name="TOC24" href="#SEC24">BACKTRACKING CONTROL</a>
-<li><a name="TOC25" href="#SEC25">CALLOUTS</a>
-<li><a name="TOC26" href="#SEC26">SEE ALSO</a>
-<li><a name="TOC27" href="#SEC27">AUTHOR</a>
-<li><a name="TOC28" href="#SEC28">REVISION</a>
+<li><a name="TOC20" href="#SEC20">NON-ATOMIC LOOKAROUND ASSERTIONS</a>
+<li><a name="TOC21" href="#SEC21">SCRIPT RUNS</a>
+<li><a name="TOC22" href="#SEC22">BACKREFERENCES</a>
+<li><a name="TOC23" href="#SEC23">SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)</a>
+<li><a name="TOC24" href="#SEC24">CONDITIONAL PATTERNS</a>
+<li><a name="TOC25" href="#SEC25">BACKTRACKING CONTROL</a>
+<li><a name="TOC26" href="#SEC26">CALLOUTS</a>
+<li><a name="TOC27" href="#SEC27">SEE ALSO</a>
+<li><a name="TOC28" href="#SEC28">AUTHOR</a>
+<li><a name="TOC29" href="#SEC29">REVISION</a>
</ul>
<br><a name="SEC1" href="#TOC1">PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY</a><br>
<P>
@@ -544,9 +545,20 @@
</pre>
Each top-level branch of a lookbehind must be of a fixed length.
</P>
-<br><a name="SEC20" href="#TOC1">SCRIPT RUNS</a><br>
+<br><a name="SEC20" href="#TOC1">NON-ATOMIC LOOKAROUND ASSERTIONS</a><br>
<P>
+These assertions are specific to PCRE2 and are not Perl-compatible.
<pre>
+ (*napla:...)
+ (*non_atomic_positive_lookahead:...)
+
+ (*naplb:...)
+ (*non_atomic_positive_lookbehind:...)
+</PRE>
+</P>
+<br><a name="SEC21" href="#TOC1">SCRIPT RUNS</a><br>
+<P>
+<pre>
(*script_run:...) ) script run, can be backtracked into
(*sr:...) )
@@ -554,7 +566,7 @@
(*asr:...) )
</PRE>
</P>
-<br><a name="SEC21" href="#TOC1">BACKREFERENCES</a><br>
+<br><a name="SEC22" href="#TOC1">BACKREFERENCES</a><br>
<P>
<pre>
\n reference by number (can be ambiguous)
@@ -571,7 +583,7 @@
(?P=name) reference by name (Python)
</PRE>
</P>
-<br><a name="SEC22" href="#TOC1">SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)</a><br>
+<br><a name="SEC23" href="#TOC1">SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)</a><br>
<P>
<pre>
(?R) recurse whole pattern
@@ -590,7 +602,7 @@
\g'-n' call subroutine by relative number (PCRE2 extension)
</PRE>
</P>
-<br><a name="SEC23" href="#TOC1">CONDITIONAL PATTERNS</a><br>
+<br><a name="SEC24" href="#TOC1">CONDITIONAL PATTERNS</a><br>
<P>
<pre>
(?(condition)yes-pattern)
@@ -613,7 +625,7 @@
conditions or recursion tests. Such a condition is interpreted as a reference
condition if the relevant named group exists.
</P>
-<br><a name="SEC24" href="#TOC1">BACKTRACKING CONTROL</a><br>
+<br><a name="SEC25" href="#TOC1">BACKTRACKING CONTROL</a><br>
<P>
All backtracking control verbs may be in the form (*VERB:NAME). For (*MARK) the
name is mandatory, for the others it is optional. (*SKIP) changes its behaviour
@@ -640,7 +652,7 @@
The effect of one of these verbs in a group called as a subroutine is confined
to the subroutine call.
</P>
-<br><a name="SEC25" href="#TOC1">CALLOUTS</a><br>
+<br><a name="SEC26" href="#TOC1">CALLOUTS</a><br>
<P>
<pre>
(?C) callout (assumed number 0)
@@ -651,12 +663,12 @@
start and the end), and the starting delimiter { matched with the ending
delimiter }. To encode the ending delimiter within the string, double it.
</P>
-<br><a name="SEC26" href="#TOC1">SEE ALSO</a><br>
+<br><a name="SEC27" href="#TOC1">SEE ALSO</a><br>
<P>
<b>pcre2pattern</b>(3), <b>pcre2api</b>(3), <b>pcre2callout</b>(3),
<b>pcre2matching</b>(3), <b>pcre2</b>(3).
</P>
-<br><a name="SEC27" href="#TOC1">AUTHOR</a><br>
+<br><a name="SEC28" href="#TOC1">AUTHOR</a><br>
<P>
Philip Hazel
<br>
@@ -665,9 +677,9 @@
Cambridge, England.
<br>
</P>
-<br><a name="SEC28" href="#TOC1">REVISION</a><br>
+<br><a name="SEC29" href="#TOC1">REVISION</a><br>
<P>
-Last updated: 11 February 2019
+Last updated: 12 July 2019
<br>
Copyright © 1997-2019 University of Cambridge.
<br>
Modified: code/trunk/doc/pcre2.txt
===================================================================
--- code/trunk/doc/pcre2.txt 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/doc/pcre2.txt 2019-07-13 11:12:03 UTC (rev 1130)
@@ -4887,6 +4887,10 @@
at the start of a pattern that set overall options that cannot be
changed within the pattern.
+ (m) PCRE2 supports non-atomic positive lookaround assertions. This is
+ an extension to the lookaround facilities. The default, Perl-compatible
+ lookarounds are atomic.
+
18. The Perl /a modifier restricts /d numbers to pure ascii, and the
/aa modifier restricts /i case-insensitive matching to pure ascii, ig-
noring Unicode rules. This separation cannot be represented with
@@ -4909,7 +4913,7 @@
REVISION
- Last updated: 12 February 2019
+ Last updated: 13 July 2019
Copyright (c) 1997-2019 University of Cambridge.
------------------------------------------------------------------------------
@@ -8140,66 +8144,69 @@
sertion may be positive (must match for the assertion to be true) or
negative (must not match for the assertion to be true). An assertion
group is matched in the normal way, and if it is true, matching contin-
- ues after it, but with the matching position in the subject string is
- was it was before the assertion was processed.
+ ues after it, but with the matching position in the subject string re-
+ set to what it was before the assertion was processed.
- A lookaround assertion may also appear as the condition in a condi-
- tional group (see below). In this case, the result of matching the as-
- sertion determines which branch of the condition is followed.
+ The Perl-compatible lookaround assertions are atomic. If an assertion
+ is true, but there is a subsequent matching failure, there is no back-
+ tracking into the assertion. However, there are some cases where non-
+ atomic assertions can be useful. PCRE2 has some support for these, de-
+ scribed in the section entitled "Non-atomic assertions" below, but they
+ are not Perl-compatible.
- Lookaround assertions are atomic. If an assertion is true, but there is
- a subsequent matching failure, there is no backtracking into the asser-
- tion.
+ A lookaround assertion may appear as the condition in a conditional
+ group (see below). In this case, the result of matching the assertion
+ determines which branch of the condition is followed.
- Assertion groups are not capture groups. If an assertion contains cap-
- ture groups within it, these are counted for the purposes of numbering
- the capture groups in the whole pattern. Within each branch of an as-
- sertion, locally captured substrings may be referenced in the usual
- way. For example, a sequence such as (.)\g{-1} can be used to check
+ Assertion groups are not capture groups. If an assertion contains cap-
+ ture groups within it, these are counted for the purposes of numbering
+ the capture groups in the whole pattern. Within each branch of an as-
+ sertion, locally captured substrings may be referenced in the usual
+ way. For example, a sequence such as (.)\g{-1} can be used to check
that two adjacent characters are the same.
- When a branch within an assertion fails to match, any substrings that
- were captured are discarded (as happens with any pattern branch that
- fails to match). A negative assertion is true only when all its
+ When a branch within an assertion fails to match, any substrings that
+ were captured are discarded (as happens with any pattern branch that
+ fails to match). A negative assertion is true only when all its
branches fail to match; this means that no captured substrings are ever
- retained after a successful negative assertion. When an assertion con-
+ retained after a successful negative assertion. When an assertion con-
tains a matching branch, what happens depends on the type of assertion.
- For a positive assertion, internally captured substrings in the suc-
- cessful branch are retained, and matching continues with the next pat-
- tern item after the assertion. For a negative assertion, a matching
- branch means that the assertion is not true. If such an assertion is
- being used as a condition in a conditional group (see below), captured
- substrings are retained, because matching continues with the "no"
+ For a positive assertion, internally captured substrings in the suc-
+ cessful branch are retained, and matching continues with the next pat-
+ tern item after the assertion. For a negative assertion, a matching
+ branch means that the assertion is not true. If such an assertion is
+ being used as a condition in a conditional group (see below), captured
+ substrings are retained, because matching continues with the "no"
branch of the condition. For other failing negative assertions, control
passes to the previous backtracking point, thus discarding any captured
strings within the assertion.
- For compatibility with Perl, most assertion groups may be repeated;
- though it makes no sense to assert the same thing several times, the
+ For compatibility with Perl, most assertion groups may be repeated;
+ though it makes no sense to assert the same thing several times, the
side effect of capturing may occasionally be useful. However, an asser-
- tion that forms the condition for a conditional group may not be quan-
+ tion that forms the condition for a conditional group may not be quan-
tified. In practice, for other assertions, there only three cases:
- (1) If the quantifier is {0}, the assertion is never obeyed during
- matching. However, it may contain internal capture groups that are
+ (1) If the quantifier is {0}, the assertion is never obeyed during
+ matching. However, it may contain internal capture groups that are
called from elsewhere via the subroutine mechanism.
- (2) If quantifier is {0,n} where n is greater than zero, it is treated
- as if it were {0,1}. At run time, the rest of the pattern match is
+ (2) If quantifier is {0,n} where n is greater than zero, it is treated
+ as if it were {0,1}. At run time, the rest of the pattern match is
tried with and without the assertion, the order depending on the greed-
iness of the quantifier.
- (3) If the minimum repetition is greater than zero, the quantifier is
- ignored. The assertion is obeyed just once when encountered during
+ (3) If the minimum repetition is greater than zero, the quantifier is
+ ignored. The assertion is obeyed just once when encountered during
matching.
Alphabetic assertion names
- Traditionally, symbolic sequences such as (?= and (?<= have been used
- to specify lookaround assertions. Perl 5.28 introduced some experimen-
+ Traditionally, symbolic sequences such as (?= and (?<= have been used
+ to specify lookaround assertions. Perl 5.28 introduced some experimen-
tal alphabetic alternatives which might be easier to remember. They all
- start with (* instead of (? and must be written using lower case let-
+ start with (* instead of (? and must be written using lower case let-
ters. PCRE2 supports the following synonyms:
(*positive_lookahead: or (*pla: is the same as (?=
@@ -8207,8 +8214,8 @@
(*positive_lookbehind: or (*plb: is the same as (?<=
(*negative_lookbehind: or (*nlb: is the same as (?<!
- For example, (*pla:foo) is the same assertion as (?=foo). In the fol-
- lowing sections, the various assertions are described using the origi-
+ For example, (*pla:foo) is the same assertion as (?=foo). In the fol-
+ lowing sections, the various assertions are described using the origi-
nal symbolic forms.
Lookahead assertions
@@ -8218,38 +8225,38 @@
\w+(?=;)
- matches a word followed by a semicolon, but does not include the semi-
+ matches a word followed by a semicolon, but does not include the semi-
colon in the match, and
foo(?!bar)
- matches any occurrence of "foo" that is not followed by "bar". Note
+ matches any occurrence of "foo" that is not followed by "bar". Note
that the apparently similar pattern
(?!foo)bar
- does not find an occurrence of "bar" that is preceded by something
- other than "foo"; it finds any occurrence of "bar" whatsoever, because
+ does not find an occurrence of "bar" that is preceded by something
+ other than "foo"; it finds any occurrence of "bar" whatsoever, because
the assertion (?!foo) is always true when the next three characters are
"bar". A lookbehind assertion is needed to achieve the other effect.
If you want to force a matching failure at some point in a pattern, the
- most convenient way to do it is with (?!) because an empty string al-
- ways matches, so an assertion that requires there not to be an empty
+ most convenient way to do it is with (?!) because an empty string al-
+ ways matches, so an assertion that requires there not to be an empty
string must always fail. The backtracking control verb (*FAIL) or (*F)
is a synonym for (?!).
Lookbehind assertions
- Lookbehind assertions start with (?<= for positive assertions and (?<!
+ Lookbehind assertions start with (?<= for positive assertions and (?<!
for negative assertions. For example,
(?<!foo)bar
- does find an occurrence of "bar" that is not preceded by "foo". The
- contents of a lookbehind assertion are restricted such that all the
+ does find an occurrence of "bar" that is not preceded by "foo". The
+ contents of a lookbehind assertion are restricted such that all the
strings it matches must have a fixed length. However, if there are sev-
- eral top-level alternatives, they do not all have to have the same
+ eral top-level alternatives, they do not all have to have the same
fixed length. Thus
(?<=bullock|donkey)
@@ -8258,66 +8265,66 @@
(?<!dogs?|cats?)
- causes an error at compile time. Branches that match different length
- strings are permitted only at the top level of a lookbehind assertion.
+ causes an error at compile time. Branches that match different length
+ strings are permitted only at the top level of a lookbehind assertion.
This is an extension compared with Perl, which requires all branches to
match the same length of string. An assertion such as
(?<=ab(c|de))
- is not permitted, because its single top-level branch can match two
- different lengths, but it is acceptable to PCRE2 if rewritten to use
+ is not permitted, because its single top-level branch can match two
+ different lengths, but it is acceptable to PCRE2 if rewritten to use
two top-level branches:
(?<=abc|abde)
- In some cases, the escape sequence \K (see above) can be used instead
+ In some cases, the escape sequence \K (see above) can be used instead
of a lookbehind assertion to get round the fixed-length restriction.
- The implementation of lookbehind assertions is, for each alternative,
- to temporarily move the current position back by the fixed length and
+ The implementation of lookbehind assertions is, for each alternative,
+ to temporarily move the current position back by the fixed length and
then try to match. If there are insufficient characters before the cur-
rent position, the assertion fails.
- In UTF-8 and UTF-16 modes, PCRE2 does not allow the \C escape (which
- matches a single code unit even in a UTF mode) to appear in lookbehind
- assertions, because it makes it impossible to calculate the length of
- the lookbehind. The \X and \R escapes, which can match different num-
+ In UTF-8 and UTF-16 modes, PCRE2 does not allow the \C escape (which
+ matches a single code unit even in a UTF mode) to appear in lookbehind
+ assertions, because it makes it impossible to calculate the length of
+ the lookbehind. The \X and \R escapes, which can match different num-
bers of code units, are never permitted in lookbehinds.
- "Subroutine" calls (see below) such as (?2) or (?&X) are permitted in
+ "Subroutine" calls (see below) such as (?2) or (?&X) are permitted in
lookbehinds, as long as the called capture group matches a fixed-length
- string. However, recursion, that is, a "subroutine" call into a group
+ string. However, recursion, that is, a "subroutine" call into a group
that is already active, is not supported.
Perl does not support backreferences in lookbehinds. PCRE2 does support
- them, but only if certain conditions are met. The PCRE2_MATCH_UN-
- SET_BACKREF option must not be set, there must be no use of (?| in the
- pattern (it creates duplicate group numbers), and if the backreference
- is by name, the name must be unique. Of course, the referenced group
- must itself match a fixed length substring. The following pattern
- matches words containing at least two characters that begin and end
+ them, but only if certain conditions are met. The PCRE2_MATCH_UN-
+ SET_BACKREF option must not be set, there must be no use of (?| in the
+ pattern (it creates duplicate group numbers), and if the backreference
+ is by name, the name must be unique. Of course, the referenced group
+ must itself match a fixed length substring. The following pattern
+ matches words containing at least two characters that begin and end
with the same character:
\b(\w)\w++(?<=\1)
- Possessive quantifiers can be used in conjunction with lookbehind as-
- sertions to specify efficient matching of fixed-length strings at the
+ Possessive quantifiers can be used in conjunction with lookbehind as-
+ sertions to specify efficient matching of fixed-length strings at the
end of subject strings. Consider a simple pattern such as
abcd$
- when applied to a long string that does not match. Because matching
- proceeds from left to right, PCRE2 will look for each "a" in the sub-
- ject and then see if what follows matches the rest of the pattern. If
+ when applied to a long string that does not match. Because matching
+ proceeds from left to right, PCRE2 will look for each "a" in the sub-
+ ject and then see if what follows matches the rest of the pattern. If
the pattern is specified as
^.*abcd$
- the initial .* matches the entire string at first, but when this fails
+ the initial .* matches the entire string at first, but when this fails
(because there is no following "a"), it backtracks to match all but the
- last character, then all but the last two characters, and so on. Once
- again the search for "a" covers the entire string, from right to left,
+ last character, then all but the last two characters, and so on. Once
+ again the search for "a" covers the entire string, from right to left,
so we are no better off. However, if the pattern is written as
^.*+(?<=abcd)
@@ -8324,8 +8331,8 @@
there can be no backtracking for the .*+ item because of the possessive
quantifier; it can match only the entire string. The subsequent lookbe-
- hind assertion does a single test on the last four characters. If it
- fails, the match fails immediately. For long strings, this approach
+ hind assertion does a single test on the last four characters. If it
+ fails, the match fails immediately. For long strings, this approach
makes a significant difference to the processing time.
Using multiple assertions
@@ -8334,18 +8341,18 @@
(?<=\d{3})(?<!999)foo
- matches "foo" preceded by three digits that are not "999". Notice that
- each of the assertions is applied independently at the same point in
- the subject string. First there is a check that the previous three
- characters are all digits, and then there is a check that the same
+ matches "foo" preceded by three digits that are not "999". Notice that
+ each of the assertions is applied independently at the same point in
+ the subject string. First there is a check that the previous three
+ characters are all digits, and then there is a check that the same
three characters are not "999". This pattern does not match "foo" pre-
- ceded by six characters, the first of which are digits and the last
- three of which are not "999". For example, it doesn't match "123abc-
+ ceded by six characters, the first of which are digits and the last
+ three of which are not "999". For example, it doesn't match "123abc-
foo". A pattern to do that is
(?<=\d{3}...)(?<!999)foo
- This time the first assertion looks at the preceding six characters,
+ This time the first assertion looks at the preceding six characters,
checking that the first three are digits, and then the second assertion
checks that the preceding three characters are not "999".
@@ -8353,30 +8360,84 @@
(?<=(?<!foo)bar)baz
- matches an occurrence of "baz" that is preceded by "bar" which in turn
+ matches an occurrence of "baz" that is preceded by "bar" which in turn
is not preceded by "foo", while
(?<=\d{3}(?!999)...)foo
- is another pattern that matches "foo" preceded by three digits and any
+ is another pattern that matches "foo" preceded by three digits and any
three characters that are not "999".
+NON-ATOMIC ASSERTIONS
+
+ The traditional Perl-compatible lookaround assertions are atomic. That
+ is, if an assertion is true, but there is a subsequent matching fail-
+ ure, there is no backtracking into the assertion. However, there are
+ some cases where non-atomic positive assertions can be useful. PCRE2
+ provides these using the following syntax:
+
+ (*non_atomic_positive_lookahead: or (*napla:
+ (*non_atomic_positive_lookbehind: or (*naplb:
+
+ Consider the problem of finding the right-most word in a string that
+ also appears earlier in the string, that is, it must appear at least
+ twice in total. This pattern returns the required result as captured
+ substring 1:
+
+ ^(?x)(*napla: .* \b(\w++)) (?> .*? \b\1\b ){2}
+
+ For a subject such as "word1 word2 word3 word2 word3 word4" the result
+ is "word3". How does it work? At the start, ^(?x) anchors the pattern
+ and sets the "x" option, which causes white space (introduced for read-
+ ability) to be ignored. Inside the assertion, the greedy .* at first
+ consumes the entire string, but then has to backtrack until the rest of
+ the assertion can match a word, which is captured by group 1. In other
+ words, when the assertion first succeeds, it captures the right-most
+ word in the string.
+
+ The current matching point is then reset to the start of the subject,
+ and the rest of the pattern match checks for two occurrences of the
+ captured word, using an ungreedy .*? to scan from the left. If this
+ succeeds, we are done, but if the last word in the string does not oc-
+ cur twice, this part of the pattern fails. If a traditional atomic
+ lookhead (?= or (*pla: had been used, the assertion could not be re-en-
+ tered, and the whole match would fail. The pattern would succeed only
+ if the very last word in the subject was found twice.
+
+ Using a non-atomic lookahead, however, means that when the last word
+ does not occur twice in the string, the lookahead can backtrack and
+ find the second-last word, and so on, until either the match succeeds,
+ or all words have been tested.
+
+ Two conditions must be met for a non-atomic assertion to be useful: the
+ contents of one or more capturing groups must change after a backtrack
+ into the assertion, and there must be a backreference to a changed
+ group later in the pattern. If this is not the case, the rest of the
+ pattern match fails exactly as before because nothing has changed, so
+ using a non-atomic assertion just wastes resources.
+
+ Non-atomic assertions are not supported by the alternative matching
+ function pcre2_dfa_match(). They are also not supported by JIT (but may
+ be in future). Note that assertions that appear as conditions for con-
+ ditional groups (see below) must be atomic.
+
+
SCRIPT RUNS
- In concept, a script run is a sequence of characters that are all from
- the same Unicode script such as Latin or Greek. However, because some
- scripts are commonly used together, and because some diacritical and
- other marks are used with multiple scripts, it is not that simple.
+ In concept, a script run is a sequence of characters that are all from
+ the same Unicode script such as Latin or Greek. However, because some
+ scripts are commonly used together, and because some diacritical and
+ other marks are used with multiple scripts, it is not that simple.
There is a full description of the rules that PCRE2 uses in the section
entitled "Script Runs" in the pcre2unicode documentation.
- If part of a pattern is enclosed between (*script_run: or (*sr: and a
- closing parenthesis, it fails if the sequence of characters that it
- matches are not a script run. After a failure, normal backtracking oc-
- curs. Script runs can be used to detect spoofing attacks using charac-
- ters that look the same, but are from different scripts. The string
- "paypal.com" is an infamous example, where the letters could be a mix-
+ If part of a pattern is enclosed between (*script_run: or (*sr: and a
+ closing parenthesis, it fails if the sequence of characters that it
+ matches are not a script run. After a failure, normal backtracking oc-
+ curs. Script runs can be used to detect spoofing attacks using charac-
+ ters that look the same, but are from different scripts. The string
+ "paypal.com" is an infamous example, where the letters could be a mix-
ture of Latin and Cyrillic. This pattern ensures that the matched char-
acters in a sequence of non-spaces that follow white space are a script
run:
@@ -8383,23 +8444,23 @@
\s+(*sr:\S+)
- To be sure that they are all from the Latin script (for example), a
+ To be sure that they are all from the Latin script (for example), a
lookahead can be used:
\s+(?=\p{Latin})(*sr:\S+)
This works as long as the first character is expected to be a character
- in that script, and not (for example) punctuation, which is allowed
- with any script. If this is not the case, a more creative lookahead is
- needed. For example, if digits, underscore, and dots are permitted at
+ in that script, and not (for example) punctuation, which is allowed
+ with any script. If this is not the case, a more creative lookahead is
+ needed. For example, if digits, underscore, and dots are permitted at
the start:
\s+(?=[0-9_.]*\p{Latin})(*sr:\S+)
- In many cases, backtracking into a script run pattern fragment is not
- desirable. The script run can employ an atomic group to prevent this.
- Because this is a common requirement, a shorthand notation is provided
+ In many cases, backtracking into a script run pattern fragment is not
+ desirable. The script run can employ an atomic group to prevent this.
+ Because this is a common requirement, a shorthand notation is provided
by (*atomic_script_run: or (*asr:
(*asr:...) is the same as (*sr:(?>...))
@@ -8407,13 +8468,13 @@
Note that the atomic group is inside the script run. Putting it outside
would not prevent backtracking into the script run pattern.
- Support for script runs is not available if PCRE2 is compiled without
+ Support for script runs is not available if PCRE2 is compiled without
Unicode support. A compile-time error is given if any of the above con-
- structs is encountered. Script runs are not supported by the alternate
- matching function, pcre2_dfa_match() because they use the same mecha-
+ structs is encountered. Script runs are not supported by the alternate
+ matching function, pcre2_dfa_match() because they use the same mecha-
nism as capturing parentheses.
- Warning: The (*ACCEPT) control verb (see below) should not be used
+ Warning: The (*ACCEPT) control verb (see below) should not be used
within a script run group, because it causes an immediate exit from the
group, bypassing the script run checking.
@@ -8422,19 +8483,19 @@
It is possible to cause the matching process to obey a pattern fragment
conditionally or to choose between two alternative fragments, depending
- on the result of an assertion, or whether a specific capture group has
+ on the result of an assertion, or whether a specific capture group has
already been matched. The two possible forms of conditional group are:
(?(condition)yes-pattern)
(?(condition)yes-pattern|no-pattern)
- If the condition is satisfied, the yes-pattern is used; otherwise the
- no-pattern (if present) is used. An absent no-pattern is equivalent to
- an empty string (it always matches). If there are more than two alter-
- natives in the group, a compile-time error occurs. Each of the two al-
+ If the condition is satisfied, the yes-pattern is used; otherwise the
+ no-pattern (if present) is used. An absent no-pattern is equivalent to
+ an empty string (it always matches). If there are more than two alter-
+ natives in the group, a compile-time error occurs. Each of the two al-
ternatives may itself contain nested groups of any form, including con-
- ditional groups; the restriction to two alternatives applies only at
- the level of the condition itself. This pattern fragment is an example
+ ditional groups; the restriction to two alternatives applies only at
+ the level of the condition itself. This pattern fragment is an example
where the alternatives are complex:
(?(1) (A|B|C) | (D | (?(2)E|F) | E) )
@@ -8441,85 +8502,85 @@
There are five kinds of condition: references to capture groups, refer-
- ences to recursion, two pseudo-conditions called DEFINE and VERSION,
+ ences to recursion, two pseudo-conditions called DEFINE and VERSION,
and assertions.
Checking for a used capture group by number
- If the text between the parentheses consists of a sequence of digits,
- the condition is true if a capture group of that number has previously
- matched. If there is more than one capture group with the same number
- (see the earlier section about duplicate group numbers), the condition
+ If the text between the parentheses consists of a sequence of digits,
+ the condition is true if a capture group of that number has previously
+ matched. If there is more than one capture group with the same number
+ (see the earlier section about duplicate group numbers), the condition
is true if any of them have matched. An alternative notation is to pre-
cede the digits with a plus or minus sign. In this case, the group num-
- ber is relative rather than absolute. The most recently opened capture
- group can be referenced by (?(-1), the next most recent by (?(-2), and
- so on. Inside loops it can also make sense to refer to subsequent
- groups. The next capture group can be referenced as (?(+1), and so on.
- (The value zero in any of these forms is not used; it provokes a com-
+ ber is relative rather than absolute. The most recently opened capture
+ group can be referenced by (?(-1), the next most recent by (?(-2), and
+ so on. Inside loops it can also make sense to refer to subsequent
+ groups. The next capture group can be referenced as (?(+1), and so on.
+ (The value zero in any of these forms is not used; it provokes a com-
pile-time error.)
- Consider the following pattern, which contains non-significant white
- space to make it more readable (assume the PCRE2_EXTENDED option) and
+ Consider the following pattern, which contains non-significant white
+ space to make it more readable (assume the PCRE2_EXTENDED option) and
to divide it into three parts for ease of discussion:
( \( )? [^()]+ (?(1) \) )
- The first part matches an optional opening parenthesis, and if that
+ The first part matches an optional opening parenthesis, and if that
character is present, sets it as the first captured substring. The sec-
- ond part matches one or more characters that are not parentheses. The
- third part is a conditional group that tests whether or not the first
- capture group matched. If it did, that is, if subject started with an
- opening parenthesis, the condition is true, and so the yes-pattern is
- executed and a closing parenthesis is required. Otherwise, since no-
+ ond part matches one or more characters that are not parentheses. The
+ third part is a conditional group that tests whether or not the first
+ capture group matched. If it did, that is, if subject started with an
+ opening parenthesis, the condition is true, and so the yes-pattern is
+ executed and a closing parenthesis is required. Otherwise, since no-
pattern is not present, the conditional group matches nothing. In other
- words, this pattern matches a sequence of non-parentheses, optionally
+ words, this pattern matches a sequence of non-parentheses, optionally
enclosed in parentheses.
- If you were embedding this pattern in a larger one, you could use a
+ If you were embedding this pattern in a larger one, you could use a
relative reference:
...other stuff... ( \( )? [^()]+ (?(-1) \) ) ...
- This makes the fragment independent of the parentheses in the larger
+ This makes the fragment independent of the parentheses in the larger
pattern.
Checking for a used capture group by name
- Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a
- used capture group by name. For compatibility with earlier versions of
- PCRE1, which had this facility before Perl, the syntax (?(name)...) is
- also recognized. Note, however, that undelimited names consisting of
- the letter R followed by digits are ambiguous (see the following sec-
+ Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a
+ used capture group by name. For compatibility with earlier versions of
+ PCRE1, which had this facility before Perl, the syntax (?(name)...) is
+ also recognized. Note, however, that undelimited names consisting of
+ the letter R followed by digits are ambiguous (see the following sec-
tion). Rewriting the above example to use a named group gives this:
(?<OPEN> \( )? [^()]+ (?(<OPEN>) \) )
- If the name used in a condition of this kind is a duplicate, the test
- is applied to all groups of the same name, and is true if any one of
+ If the name used in a condition of this kind is a duplicate, the test
+ is applied to all groups of the same name, and is true if any one of
them has matched.
Checking for pattern recursion
- "Recursion" in this sense refers to any subroutine-like call from one
- part of the pattern to another, whether or not it is actually recur-
- sive. See the sections entitled "Recursive patterns" and "Groups as
+ "Recursion" in this sense refers to any subroutine-like call from one
+ part of the pattern to another, whether or not it is actually recur-
+ sive. See the sections entitled "Recursive patterns" and "Groups as
subroutines" below for details of recursion and subroutine calls.
- If a condition is the string (R), and there is no capture group with
- the name R, the condition is true if matching is currently in a recur-
- sion or subroutine call to the whole pattern or any capture group. If
- digits follow the letter R, and there is no group with that name, the
- condition is true if the most recent call is into a group with the
- given number, which must exist somewhere in the overall pattern. This
+ If a condition is the string (R), and there is no capture group with
+ the name R, the condition is true if matching is currently in a recur-
+ sion or subroutine call to the whole pattern or any capture group. If
+ digits follow the letter R, and there is no group with that name, the
+ condition is true if the most recent call is into a group with the
+ given number, which must exist somewhere in the overall pattern. This
is a contrived example that is equivalent to a+b:
((?(R1)a+|(?1)b))
- However, in both cases, if there is a capture group with a matching
- name, the condition tests for its being set, as described in the sec-
- tion above, instead of testing for recursion. For example, creating a
- group with the name R1 by adding (?<R1>) to the above pattern com-
+ However, in both cases, if there is a capture group with a matching
+ name, the condition tests for its being set, as described in the sec-
+ tion above, instead of testing for recursion. For example, creating a
+ group with the name R1 by adding (?<R1>) to the above pattern com-
pletely changes its meaning.
If a name preceded by ampersand follows the letter R, for example:
@@ -8526,12 +8587,12 @@
(?(R&name)...)
- the condition is true if the most recent recursion is into a group of
+ the condition is true if the most recent recursion is into a group of
that name (which must exist within the pattern).
This condition does not check the entire recursion stack. It tests only
- the current level. If the name used in a condition of this kind is a
- duplicate, the test is applied to all groups of the same name, and is
+ the current level. If the name used in a condition of this kind is a
+ duplicate, the test is applied to all groups of the same name, and is
true if any one of them is the most recent recursion.
At "top level", all these recursion test conditions are false.
@@ -8539,65 +8600,67 @@
Defining capture groups for use by reference only
If the condition is the string (DEFINE), the condition is always false,
- even if there is a group with the name DEFINE. In this case, there may
+ even if there is a group with the name DEFINE. In this case, there may
be only one alternative in the rest of the conditional group. It is al-
- ways skipped if control reaches this point in the pattern; the idea of
- DEFINE is that it can be used to define subroutines that can be refer-
- enced from elsewhere. (The use of subroutines is described below.) For
- example, a pattern to match an IPv4 address such as "192.168.23.245"
+ ways skipped if control reaches this point in the pattern; the idea of
+ DEFINE is that it can be used to define subroutines that can be refer-
+ enced from elsewhere. (The use of subroutines is described below.) For
+ example, a pattern to match an IPv4 address such as "192.168.23.245"
could be written like this (ignore white space and line breaks):
(?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
\b (?&byte) (\.(?&byte)){3} \b
- The first part of the pattern is a DEFINE group inside which a another
- group named "byte" is defined. This matches an individual component of
- an IPv4 address (a number less than 256). When matching takes place,
- this part of the pattern is skipped because DEFINE acts like a false
- condition. The rest of the pattern uses references to the named group
- to match the four dot-separated components of an IPv4 address, insist-
+ The first part of the pattern is a DEFINE group inside which a another
+ group named "byte" is defined. This matches an individual component of
+ an IPv4 address (a number less than 256). When matching takes place,
+ this part of the pattern is skipped because DEFINE acts like a false
+ condition. The rest of the pattern uses references to the named group
+ to match the four dot-separated components of an IPv4 address, insist-
ing on a word boundary at each end.
Checking the PCRE2 version
- Programs that link with a PCRE2 library can check the version by call-
- ing pcre2_config() with appropriate arguments. Users of applications
- that do not have access to the underlying code cannot do this. A spe-
- cial "condition" called VERSION exists to allow such users to discover
+ Programs that link with a PCRE2 library can check the version by call-
+ ing pcre2_config() with appropriate arguments. Users of applications
+ that do not have access to the underlying code cannot do this. A spe-
+ cial "condition" called VERSION exists to allow such users to discover
which version of PCRE2 they are dealing with by using this condition to
- match a string such as "yesno". VERSION must be followed either by "="
+ match a string such as "yesno". VERSION must be followed either by "="
or ">=" and a version number. For example:
(?(VERSION>=10.4)yes|no)
- This pattern matches "yes" if the PCRE2 version is greater or equal to
- 10.4, or "no" otherwise. The fractional part of the version number may
+ This pattern matches "yes" if the PCRE2 version is greater or equal to
+ 10.4, or "no" otherwise. The fractional part of the version number may
not contain more than two digits.
Assertion conditions
- If the condition is not in any of the above formats, it must be a
- parenthesized assertion. This may be a positive or negative lookahead
- or lookbehind assertion. Consider this pattern, again containing non-
- significant white space, and with the two alternatives on the second
- line:
+ If the condition is not in any of the above formats, it must be a
+ parenthesized assertion. This may be a positive or negative lookahead
+ or lookbehind assertion. However, it must be a traditional atomic as-
+ sertion, not one of the PCRE2-specific non-atomic assertions.
+ Consider this pattern, again containing non-significant white space,
+ and with the two alternatives on the second line:
+
(?(?=[^a-z]*[a-z])
\d{2}-[a-z]{3}-\d{2} | \d{2}-\d{2}-\d{2} )
- The condition is a positive lookahead assertion that matches an op-
+ The condition is a positive lookahead assertion that matches an op-
tional sequence of non-letters followed by a letter. In other words, it
tests for the presence of at least one letter in the subject. If a let-
- ter is found, the subject is matched against the first alternative;
- otherwise it is matched against the second. This pattern matches
- strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are
+ ter is found, the subject is matched against the first alternative;
+ otherwise it is matched against the second. This pattern matches
+ strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are
letters and dd are digits.
When an assertion that is a condition contains capture groups, any cap-
- turing that occurs in a matching branch is retained afterwards, for
- both positive and negative assertions, because matching always contin-
- ues after the assertion, whether it succeeds or fails. (Compare non-
- conditional assertions, for which captures are retained only for posi-
+ turing that occurs in a matching branch is retained afterwards, for
+ both positive and negative assertions, because matching always contin-
+ ues after the assertion, whether it succeeds or fails. (Compare non-
+ conditional assertions, for which captures are retained only for posi-
tive assertions that succeed.)
@@ -8604,44 +8667,44 @@
COMMENTS
There are two ways of including comments in patterns that are processed
- by PCRE2. In both cases, the start of the comment must not be in a
- character class, nor in the middle of any other sequence of related
- characters such as (?: or a group name or number. The characters that
+ by PCRE2. In both cases, the start of the comment must not be in a
+ character class, nor in the middle of any other sequence of related
+ characters such as (?: or a group name or number. The characters that
make up a comment play no part in the pattern matching.
- The sequence (?# marks the start of a comment that continues up to the
- next closing parenthesis. Nested parentheses are not permitted. If the
- PCRE2_EXTENDED or PCRE2_EXTENDED_MORE option is set, an unescaped #
- character also introduces a comment, which in this case continues to
- immediately after the next newline character or character sequence in
+ The sequence (?# marks the start of a comment that continues up to the
+ next closing parenthesis. Nested parentheses are not permitted. If the
+ PCRE2_EXTENDED or PCRE2_EXTENDED_MORE option is set, an unescaped #
+ character also introduces a comment, which in this case continues to
+ immediately after the next newline character or character sequence in
the pattern. Which characters are interpreted as newlines is controlled
- by an option passed to the compiling function or by a special sequence
+ by an option passed to the compiling function or by a special sequence
at the start of the pattern, as described in the section entitled "New-
line conventions" above. Note that the end of this type of comment is a
- literal newline sequence in the pattern; escape sequences that happen
+ literal newline sequence in the pattern; escape sequences that happen
to represent a newline do not count. For example, consider this pattern
- when PCRE2_EXTENDED is set, and the default newline convention (a sin-
+ when PCRE2_EXTENDED is set, and the default newline convention (a sin-
gle linefeed character) is in force:
abc #comment \n still comment
- On encountering the # character, pcre2_compile() skips along, looking
- for a newline in the pattern. The sequence \n is still literal at this
- stage, so it does not terminate the comment. Only an actual character
+ On encountering the # character, pcre2_compile() skips along, looking
+ for a newline in the pattern. The sequence \n is still literal at this
+ stage, so it does not terminate the comment. Only an actual character
with the code value 0x0a (the default newline) does so.
RECURSIVE PATTERNS
- Consider the problem of matching a string in parentheses, allowing for
- unlimited nested parentheses. Without the use of recursion, the best
- that can be done is to use a pattern that matches up to some fixed
- depth of nesting. It is not possible to handle an arbitrary nesting
+ Consider the problem of matching a string in parentheses, allowing for
+ unlimited nested parentheses. Without the use of recursion, the best
+ that can be done is to use a pattern that matches up to some fixed
+ depth of nesting. It is not possible to handle an arbitrary nesting
depth.
For some time, Perl has provided a facility that allows regular expres-
- sions to recurse (amongst other things). It does this by interpolating
- Perl code in the expression at run time, and the code can refer to the
+ sions to recurse (amongst other things). It does this by interpolating
+ Perl code in the expression at run time, and the code can refer to the
expression itself. A Perl pattern using code interpolation to solve the
parentheses problem can be created like this:
@@ -8650,67 +8713,67 @@
The (?p{...}) item interpolates Perl code at run time, and in this case
refers recursively to the pattern in which it appears.
- Obviously, PCRE2 cannot support the interpolation of Perl code. In-
- stead, it supports special syntax for recursion of the entire pattern,
+ Obviously, PCRE2 cannot support the interpolation of Perl code. In-
+ stead, it supports special syntax for recursion of the entire pattern,
and also for individual capture group recursion. After its introduction
in PCRE1 and Python, this kind of recursion was subsequently introduced
into Perl at release 5.10.
- A special item that consists of (? followed by a number greater than
- zero and a closing parenthesis is a recursive subroutine call of the
- capture group of the given number, provided that it occurs inside that
- group. (If not, it is a non-recursive subroutine call, which is de-
+ A special item that consists of (? followed by a number greater than
+ zero and a closing parenthesis is a recursive subroutine call of the
+ capture group of the given number, provided that it occurs inside that
+ group. (If not, it is a non-recursive subroutine call, which is de-
scribed in the next section.) The special item (?R) or (?0) is a recur-
sive call of the entire regular expression.
- This PCRE2 pattern solves the nested parentheses problem (assume the
+ This PCRE2 pattern solves the nested parentheses problem (assume the
PCRE2_EXTENDED option is set so that white space is ignored):
\( ( [^()]++ | (?R) )* \)
- First it matches an opening parenthesis. Then it matches any number of
- substrings which can either be a sequence of non-parentheses, or a re-
+ First it matches an opening parenthesis. Then it matches any number of
+ substrings which can either be a sequence of non-parentheses, or a re-
cursive match of the pattern itself (that is, a correctly parenthesized
- substring). Finally there is a closing parenthesis. Note the use of a
- possessive quantifier to avoid backtracking into sequences of non-
+ substring). Finally there is a closing parenthesis. Note the use of a
+ possessive quantifier to avoid backtracking into sequences of non-
parentheses.
- If this were part of a larger pattern, you would not want to recurse
+ If this were part of a larger pattern, you would not want to recurse
the entire pattern, so instead you could use this:
( \( ( [^()]++ | (?1) )* \) )
- We have put the pattern into parentheses, and caused the recursion to
+ We have put the pattern into parentheses, and caused the recursion to
refer to them instead of the whole pattern.
- In a larger pattern, keeping track of parenthesis numbers can be
- tricky. This is made easier by the use of relative references. Instead
+ In a larger pattern, keeping track of parenthesis numbers can be
+ tricky. This is made easier by the use of relative references. Instead
of (?1) in the pattern above you can write (?-2) to refer to the second
- most recently opened parentheses preceding the recursion. In other
- words, a negative number counts capturing parentheses leftwards from
+ most recently opened parentheses preceding the recursion. In other
+ words, a negative number counts capturing parentheses leftwards from
the point at which it is encountered.
- Be aware however, that if duplicate capture group numbers are in use,
- relative references refer to the earliest group with the appropriate
+ Be aware however, that if duplicate capture group numbers are in use,
+ relative references refer to the earliest group with the appropriate
number. Consider, for example:
(?|(a)|(b)) (c) (?-2)
The first two capture groups (a) and (b) are both numbered 1, and group
- (c) is number 2. When the reference (?-2) is encountered, the second
- most recently opened parentheses has the number 1, but it is the first
+ (c) is number 2. When the reference (?-2) is encountered, the second
+ most recently opened parentheses has the number 1, but it is the first
such group (the (a) group) to which the recursion refers. This would be
- the same if an absolute reference (?1) was used. In other words, rela-
+ the same if an absolute reference (?1) was used. In other words, rela-
tive references are just a shorthand for computing a group number.
- It is also possible to refer to subsequent capture groups, by writing
- references such as (?+2). However, these cannot be recursive because
- the reference is not inside the parentheses that are referenced. They
- are always non-recursive subroutine calls, as described in the next
+ It is also possible to refer to subsequent capture groups, by writing
+ references such as (?+2). However, these cannot be recursive because
+ the reference is not inside the parentheses that are referenced. They
+ are always non-recursive subroutine calls, as described in the next
section.
- An alternative approach is to use named parentheses. The Perl syntax
- for this is (?&name); PCRE1's earlier syntax (?P>name) is also sup-
+ An alternative approach is to use named parentheses. The Perl syntax
+ for this is (?&name); PCRE1's earlier syntax (?P>name) is also sup-
ported. We could rewrite the above example as follows:
(?<pn> \( ( [^()]++ | (?&pn) )* \) )
@@ -8719,40 +8782,40 @@
used.
The example pattern that we have been looking at contains nested unlim-
- ited repeats, and so the use of a possessive quantifier for matching
- strings of non-parentheses is important when applying the pattern to
+ ited repeats, and so the use of a possessive quantifier for matching
+ strings of non-parentheses is important when applying the pattern to
strings that do not match. For example, when this pattern is applied to
(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
- it yields "no match" quickly. However, if a possessive quantifier is
- not used, the match runs for a very long time indeed because there are
- so many different ways the + and * repeats can carve up the subject,
+ it yields "no match" quickly. However, if a possessive quantifier is
+ not used, the match runs for a very long time indeed because there are
+ so many different ways the + and * repeats can carve up the subject,
and all have to be tested before failure can be reported.
- At the end of a match, the values of capturing parentheses are those
- from the outermost level. If you want to obtain intermediate values, a
+ At the end of a match, the values of capturing parentheses are those
+ from the outermost level. If you want to obtain intermediate values, a
callout function can be used (see below and the pcre2callout documenta-
tion). If the pattern above is matched against
(ab(cd)ef)
- the value for the inner capturing parentheses (numbered 2) is "ef",
- which is the last value taken on at the top level. If a capture group
- is not matched at the top level, its final captured value is unset,
- even if it was (temporarily) set at a deeper level during the matching
+ the value for the inner capturing parentheses (numbered 2) is "ef",
+ which is the last value taken on at the top level. If a capture group
+ is not matched at the top level, its final captured value is unset,
+ even if it was (temporarily) set at a deeper level during the matching
process.
- Do not confuse the (?R) item with the condition (R), which tests for
- recursion. Consider this pattern, which matches text in angle brack-
- ets, allowing for arbitrary nesting. Only digits are allowed in nested
- brackets (that is, when recursing), whereas any characters are permit-
+ Do not confuse the (?R) item with the condition (R), which tests for
+ recursion. Consider this pattern, which matches text in angle brack-
+ ets, allowing for arbitrary nesting. Only digits are allowed in nested
+ brackets (that is, when recursing), whereas any characters are permit-
ted at the outer level.
< (?: (?(R) \d++ | [^<>]*+) | (?R)) * >
- In this pattern, (?(R) is the start of a conditional group, with two
- different alternatives for the recursive and non-recursive cases. The
+ In this pattern, (?(R) is the start of a conditional group, with two
+ different alternatives for the recursive and non-recursive cases. The
(?R) item is the actual recursive call.
Differences in recursion processing between PCRE2 and Perl
@@ -8759,17 +8822,17 @@
Some former differences between PCRE2 and Perl no longer exist.
- Before release 10.30, recursion processing in PCRE2 differed from Perl
- in that a recursive subroutine call was always treated as an atomic
- group. That is, once it had matched some of the subject string, it was
- never re-entered, even if it contained untried alternatives and there
- was a subsequent matching failure. (Historical note: PCRE implemented
+ Before release 10.30, recursion processing in PCRE2 differed from Perl
+ in that a recursive subroutine call was always treated as an atomic
+ group. That is, once it had matched some of the subject string, it was
+ never re-entered, even if it contained untried alternatives and there
+ was a subsequent matching failure. (Historical note: PCRE implemented
recursion before Perl did.)
- Starting with release 10.30, recursive subroutine calls are no longer
+ Starting with release 10.30, recursive subroutine calls are no longer
treated as atomic. That is, they can be re-entered to try unused alter-
- natives if there is a matching failure later in the pattern. This is
- now compatible with the way Perl works. If you want a subroutine call
+ natives if there is a matching failure later in the pattern. This is
+ now compatible with the way Perl works. If you want a subroutine call
to be atomic, you must explicitly enclose it in an atomic group.
Supporting backtracking into recursions simplifies certain types of re-
@@ -8777,47 +8840,47 @@
^((.)(?1)\2|.?)$
- The second branch in the group matches a single central character in
- the palindrome when there are an odd number of characters, or nothing
- when there are an even number of characters, but in order to work it
- has to be able to try the second case when the rest of the pattern
+ The second branch in the group matches a single central character in
+ the palindrome when there are an odd number of characters, or nothing
+ when there are an even number of characters, but in order to work it
+ has to be able to try the second case when the rest of the pattern
match fails. If you want to match typical palindromic phrases, the pat-
- tern has to ignore all non-word characters, which can be done like
+ tern has to ignore all non-word characters, which can be done like
this:
^\W*+((.)\W*+(?1)\W*+\2|\W*+.?)\W*+$
- If run with the PCRE2_CASELESS option, this pattern matches phrases
- such as "A man, a plan, a canal: Panama!". Note the use of the posses-
- sive quantifier *+ to avoid backtracking into sequences of non-word
+ If run with the PCRE2_CASELESS option, this pattern matches phrases
+ such as "A man, a plan, a canal: Panama!". Note the use of the posses-
+ sive quantifier *+ to avoid backtracking into sequences of non-word
characters. Without this, PCRE2 takes a great deal longer (ten times or
- more) to match typical phrases, and Perl takes so long that you think
+ more) to match typical phrases, and Perl takes so long that you think
it has gone into a loop.
- Another way in which PCRE2 and Perl used to differ in their recursion
- processing is in the handling of captured values. Formerly in Perl,
- when a group was called recursively or as a subroutine (see the next
+ Another way in which PCRE2 and Perl used to differ in their recursion
+ processing is in the handling of captured values. Formerly in Perl,
+ when a group was called recursively or as a subroutine (see the next
section), it had no access to any values that were captured outside the
- recursion, whereas in PCRE2 these values can be referenced. Consider
+ recursion, whereas in PCRE2 these values can be referenced. Consider
this pattern:
^(.)(\1|a(?2))
- This pattern matches "bab". The first capturing parentheses match "b",
+ This pattern matches "bab". The first capturing parentheses match "b",
then in the second group, when the backreference \1 fails to match "b",
the second alternative matches "a" and then recurses. In the recursion,
- \1 does now match "b" and so the whole match succeeds. This match used
+ \1 does now match "b" and so the whole match succeeds. This match used
to fail in Perl, but in later versions (I tried 5.024) it now works.
GROUPS AS SUBROUTINES
- If the syntax for a recursive group call (either by number or by name)
- is used outside the parentheses to which it refers, it operates a bit
- like a subroutine in a programming language. More accurately, PCRE2
+ If the syntax for a recursive group call (either by number or by name)
+ is used outside the parentheses to which it refers, it operates a bit
+ like a subroutine in a programming language. More accurately, PCRE2
treats the referenced group as an independent subpattern which it tries
- to match at the current matching position. The called group may be de-
- fined before or after the reference. A numbered reference can be abso-
+ to match at the current matching position. The called group may be de-
+ fined before or after the reference. A numbered reference can be abso-
lute or relative, as in these examples:
(...(absolute)...)...(?2)...
@@ -8828,30 +8891,30 @@
(sens|respons)e and \1ibility
- matches "sense and sensibility" and "response and responsibility", but
+ matches "sense and sensibility" and "response and responsibility", but
not "sense and responsibility". If instead the pattern
(sens|respons)e and (?1)ibility
- is used, it does match "sense and responsibility" as well as the other
- two strings. Another example is given in the discussion of DEFINE
+ is used, it does match "sense and responsibility" as well as the other
+ two strings. Another example is given in the discussion of DEFINE
above.
- Like recursions, subroutine calls used to be treated as atomic, but
- this changed at PCRE2 release 10.30, so backtracking into subroutine
- calls can now occur. However, any capturing parentheses that are set
+ Like recursions, subroutine calls used to be treated as atomic, but
+ this changed at PCRE2 release 10.30, so backtracking into subroutine
+ calls can now occur. However, any capturing parentheses that are set
during the subroutine call revert to their previous values afterwards.
- Processing options such as case-independence are fixed when a group is
- defined, so if it is used as a subroutine, such options cannot be
+ Processing options such as case-independence are fixed when a group is
+ defined, so if it is used as a subroutine, such options cannot be
changed for different calls. For example, consider this pattern:
(abc)(?i:(?-1))
- It matches "abcabc". It does not match "abcABC" because the change of
+ It matches "abcabc". It does not match "abcABC" because the change of
processing option does not affect the called group.
- The behaviour of backtracking control verbs in groups when called as
+ The behaviour of backtracking control verbs in groups when called as
subroutines is described in the section entitled "Backtracking verbs in
subroutines" below.
@@ -8858,22 +8921,22 @@
ONIGURUMA SUBROUTINE SYNTAX
- For compatibility with Oniguruma, the non-Perl syntax \g followed by a
+ For compatibility with Oniguruma, the non-Perl syntax \g followed by a
name or a number enclosed either in angle brackets or single quotes, is
an alternative syntax for calling a group as a subroutine, possibly re-
- cursively. Here are two of the examples used above, rewritten using
+ cursively. Here are two of the examples used above, rewritten using
this syntax:
(?<pn> \( ( (?>[^()]+) | \g<pn> )* \) )
(sens|respons)e and \g'1'ibility
- PCRE2 supports an extension to Oniguruma: if a number is preceded by a
+ PCRE2 supports an extension to Oniguruma: if a number is preceded by a
plus or a minus sign it is taken as a relative reference. For example:
(abc)(?i:\g<-1>)
- Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not
- synonymous. The former is a backreference; the latter is a subroutine
+ Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not
+ synonymous. The former is a backreference; the latter is a subroutine
call.
@@ -8880,54 +8943,54 @@
CALLOUTS
Perl has a feature whereby using the sequence (?{...}) causes arbitrary
- Perl code to be obeyed in the middle of matching a regular expression.
+ Perl code to be obeyed in the middle of matching a regular expression.
This makes it possible, amongst other things, to extract different sub-
strings that match the same pair of parentheses when there is a repeti-
tion.
- PCRE2 provides a similar feature, but of course it cannot obey arbi-
- trary Perl code. The feature is called "callout". The caller of PCRE2
- provides an external function by putting its entry point in a match
- context using the function pcre2_set_callout(), and then passing that
- context to pcre2_match() or pcre2_dfa_match(). If no match context is
+ PCRE2 provides a similar feature, but of course it cannot obey arbi-
+ trary Perl code. The feature is called "callout". The caller of PCRE2
+ provides an external function by putting its entry point in a match
+ context using the function pcre2_set_callout(), and then passing that
+ context to pcre2_match() or pcre2_dfa_match(). If no match context is
passed, or if the callout entry point is set to NULL, callouts are dis-
abled.
- Within a regular expression, (?C<arg>) indicates a point at which the
- external function is to be called. There are two kinds of callout:
- those with a numerical argument and those with a string argument. (?C)
- on its own with no argument is treated as (?C0). A numerical argument
- allows the application to distinguish between different callouts.
- String arguments were added for release 10.20 to make it possible for
- script languages that use PCRE2 to embed short scripts within patterns
+ Within a regular expression, (?C<arg>) indicates a point at which the
+ external function is to be called. There are two kinds of callout:
+ those with a numerical argument and those with a string argument. (?C)
+ on its own with no argument is treated as (?C0). A numerical argument
+ allows the application to distinguish between different callouts.
+ String arguments were added for release 10.20 to make it possible for
+ script languages that use PCRE2 to embed short scripts within patterns
in a similar way to Perl.
During matching, when PCRE2 reaches a callout point, the external func-
- tion is called. It is provided with the number or string argument of
- the callout, the position in the pattern, and one item of data that is
+ tion is called. It is provided with the number or string argument of
+ the callout, the position in the pattern, and one item of data that is
also set in the match block. The callout function may cause matching to
proceed, to backtrack, or to fail.
- By default, PCRE2 implements a number of optimizations at matching
- time, and one side-effect is that sometimes callouts are skipped. If
- you need all possible callouts to happen, you need to set options that
- disable the relevant optimizations. More details, including a complete
- description of the programming interface to the callout function, are
+ By default, PCRE2 implements a number of optimizations at matching
+ time, and one side-effect is that sometimes callouts are skipped. If
+ you need all possible callouts to happen, you need to set options that
+ disable the relevant optimizations. More details, including a complete
+ description of the programming interface to the callout function, are
given in the pcre2callout documentation.
Callouts with numerical arguments
- If you just want to have a means of identifying different callout
- points, put a number less than 256 after the letter C. For example,
+ If you just want to have a means of identifying different callout
+ points, put a number less than 256 after the letter C. For example,
this pattern has two callout points:
(?C1)abc(?C2)def
- If the PCRE2_AUTO_CALLOUT flag is passed to pcre2_compile(), numerical
- callouts are automatically installed before each item in the pattern.
- They are all numbered 255. If there is a conditional group in the pat-
+ If the PCRE2_AUTO_CALLOUT flag is passed to pcre2_compile(), numerical
+ callouts are automatically installed before each item in the pattern.
+ They are all numbered 255. If there is a conditional group in the pat-
tern whose condition is an assertion, an additional callout is inserted
- just before the condition. An explicit callout may also be set at this
+ just before the condition. An explicit callout may also be set at this
position, as in this example:
(?(?C9)(?=a)abc|def)
@@ -8937,62 +9000,62 @@
Callouts with string arguments
- A delimited string may be used instead of a number as a callout argu-
- ment. The starting delimiter must be one of ` ' " ^ % # $ { and the
+ A delimited string may be used instead of a number as a callout argu-
+ ment. The starting delimiter must be one of ` ' " ^ % # $ { and the
ending delimiter is the same as the start, except for {, where the end-
- ing delimiter is }. If the ending delimiter is needed within the
+ ing delimiter is }. If the ending delimiter is needed within the
string, it must be doubled. For example:
(?C'ab ''c'' d')xyz(?C{any text})pqr
- The doubling is removed before the string is passed to the callout
+ The doubling is removed before the string is passed to the callout
function.
BACKTRACKING CONTROL
- There are a number of special "Backtracking Control Verbs" (to use
- Perl's terminology) that modify the behaviour of backtracking during
- matching. They are generally of the form (*VERB) or (*VERB:NAME). Some
+ There are a number of special "Backtracking Control Verbs" (to use
+ Perl's terminology) that modify the behaviour of backtracking during
+ matching. They are generally of the form (*VERB) or (*VERB:NAME). Some
verbs take either form, and may behave differently depending on whether
- or not a name argument is present. The names are not required to be
+ or not a name argument is present. The names are not required to be
unique within the pattern.
- By default, for compatibility with Perl, a name is any sequence of
+ By default, for compatibility with Perl, a name is any sequence of
characters that does not include a closing parenthesis. The name is not
- processed in any way, and it is not possible to include a closing
- parenthesis in the name. This can be changed by setting the
- PCRE2_ALT_VERBNAMES option, but the result is no longer Perl-compati-
+ processed in any way, and it is not possible to include a closing
+ parenthesis in the name. This can be changed by setting the
+ PCRE2_ALT_VERBNAMES option, but the result is no longer Perl-compati-
ble.
- When PCRE2_ALT_VERBNAMES is set, backslash processing is applied to
- verb names and only an unescaped closing parenthesis terminates the
- name. However, the only backslash items that are permitted are \Q, \E,
- and sequences such as \x{100} that define character code points. Char-
+ When PCRE2_ALT_VERBNAMES is set, backslash processing is applied to
+ verb names and only an unescaped closing parenthesis terminates the
+ name. However, the only backslash items that are permitted are \Q, \E,
+ and sequences such as \x{100} that define character code points. Char-
acter type escapes such as \d are faulted.
A closing parenthesis can be included in a name either as \) or between
- \Q and \E. In addition to backslash processing, if the PCRE2_EXTENDED
+ \Q and \E. In addition to backslash processing, if the PCRE2_EXTENDED
or PCRE2_EXTENDED_MORE option is also set, unescaped whitespace in verb
names is skipped, and #-comments are recognized, exactly as in the rest
- of the pattern. PCRE2_EXTENDED and PCRE2_EXTENDED_MORE do not affect
+ of the pattern. PCRE2_EXTENDED and PCRE2_EXTENDED_MORE do not affect
verb names unless PCRE2_ALT_VERBNAMES is also set.
- The maximum length of a name is 255 in the 8-bit library and 65535 in
- the 16-bit and 32-bit libraries. If the name is empty, that is, if the
- closing parenthesis immediately follows the colon, the effect is as if
+ The maximum length of a name is 255 in the 8-bit library and 65535 in
+ the 16-bit and 32-bit libraries. If the name is empty, that is, if the
+ closing parenthesis immediately follows the colon, the effect is as if
the colon were not there. Any number of these verbs may occur in a pat-
tern. Except for (*ACCEPT), they may not be quantified.
- Since these verbs are specifically related to backtracking, most of
- them can be used only when the pattern is to be matched using the tra-
+ Since these verbs are specifically related to backtracking, most of
+ them can be used only when the pattern is to be matched using the tra-
ditional matching function, because that uses a backtracking algorithm.
- With the exception of (*FAIL), which behaves like a failing negative
+ With the exception of (*FAIL), which behaves like a failing negative
assertion, the backtracking control verbs cause an error if encountered
by the DFA matching function.
- The behaviour of these verbs in repeated groups, assertions, and in
- capture groups called as subroutines (whether or not recursively) is
+ The behaviour of these verbs in repeated groups, assertions, and in
+ capture groups called as subroutines (whether or not recursively) is
documented below.
Optimizations that affect backtracking verbs
@@ -8999,16 +9062,16 @@
PCRE2 contains some optimizations that are used to speed up matching by
running some checks at the start of each match attempt. For example, it
- may know the minimum length of matching subject, or that a particular
+ may know the minimum length of matching subject, or that a particular
character must be present. When one of these optimizations bypasses the
- running of a match, any included backtracking verbs will not, of
+ running of a match, any included backtracking verbs will not, of
course, be processed. You can suppress the start-of-match optimizations
- by setting the PCRE2_NO_START_OPTIMIZE option when calling pcre2_com-
- pile(), or by starting the pattern with (*NO_START_OPT). There is more
+ by setting the PCRE2_NO_START_OPTIMIZE option when calling pcre2_com-
+ pile(), or by starting the pattern with (*NO_START_OPT). There is more
discussion of this option in the section entitled "Compiling a pattern"
in the pcre2api documentation.
- Experiments with Perl suggest that it too has similar optimizations,
+ Experiments with Perl suggest that it too has similar optimizations,
and like PCRE2, turning them off can change the result of a match.
Verbs that act immediately
@@ -9017,77 +9080,77 @@
(*ACCEPT) or (*ACCEPT:NAME)
- This verb causes the match to end successfully, skipping the remainder
- of the pattern. However, when it is inside a capture group that is
+ This verb causes the match to end successfully, skipping the remainder
+ of the pattern. However, when it is inside a capture group that is
called as a subroutine, only that group is ended successfully. Matching
then continues at the outer level. If (*ACCEPT) in triggered in a posi-
- tive assertion, the assertion succeeds; in a negative assertion, the
+ tive assertion, the assertion succeeds; in a negative assertion, the
assertion fails.
- If (*ACCEPT) is inside capturing parentheses, the data so far is cap-
+ If (*ACCEPT) is inside capturing parentheses, the data so far is cap-
tured. For example:
A((?:A|B(*ACCEPT)|C)D)
- This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap-
+ This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap-
tured by the outer parentheses.
- (*ACCEPT) is the only backtracking verb that is allowed to be quanti-
- fied because an ungreedy quantification with a minimum of zero acts
+ (*ACCEPT) is the only backtracking verb that is allowed to be quanti-
+ fied because an ungreedy quantification with a minimum of zero acts
only when a backtrack happens. Consider, for example,
(A(*ACCEPT)??B)C
- where A, B, and C may be complex expressions. After matching "A", the
- matcher processes "BC"; if that fails, causing a backtrack, (*ACCEPT)
- is triggered and the match succeeds. In both cases, all but C is cap-
- tured. Whereas (*COMMIT) (see below) means "fail on backtrack", a re-
+ where A, B, and C may be complex expressions. After matching "A", the
+ matcher processes "BC"; if that fails, causing a backtrack, (*ACCEPT)
+ is triggered and the match succeeds. In both cases, all but C is cap-
+ tured. Whereas (*COMMIT) (see below) means "fail on backtrack", a re-
peated (*ACCEPT) of this type means "succeed on backtrack".
- Warning: (*ACCEPT) should not be used within a script run group, be-
- cause it causes an immediate exit from the group, bypassing the script
+ Warning: (*ACCEPT) should not be used within a script run group, be-
+ cause it causes an immediate exit from the group, bypassing the script
run checking.
(*FAIL) or (*FAIL:NAME)
- This verb causes a matching failure, forcing backtracking to occur. It
- may be abbreviated to (*F). It is equivalent to (?!) but easier to
+ This verb causes a matching failure, forcing backtracking to occur. It
+ may be abbreviated to (*F). It is equivalent to (?!) but easier to
read. The Perl documentation notes that it is probably useful only when
combined with (?{}) or (??{}). Those are, of course, Perl features that
- are not present in PCRE2. The nearest equivalent is the callout fea-
+ are not present in PCRE2. The nearest equivalent is the callout fea-
ture, as for example in this pattern:
a+(?C)(*FAIL)
- A match with the string "aaaa" always fails, but the callout is taken
+ A match with the string "aaaa" always fails, but the callout is taken
before each backtrack happens (in this example, 10 times).
- (*ACCEPT:NAME) and (*FAIL:NAME) behave the same as (*MARK:NAME)(*AC-
- CEPT) and (*MARK:NAME)(*FAIL), respectively, that is, a (*MARK) is
+ (*ACCEPT:NAME) and (*FAIL:NAME) behave the same as (*MARK:NAME)(*AC-
+ CEPT) and (*MARK:NAME)(*FAIL), respectively, that is, a (*MARK) is
recorded just before the verb acts.
Recording which path was taken
- There is one verb whose main purpose is to track how a match was ar-
- rived at, though it also has a secondary use in conjunction with ad-
+ There is one verb whose main purpose is to track how a match was ar-
+ rived at, though it also has a secondary use in conjunction with ad-
vancing the match starting point (see (*SKIP) below).
(*MARK:NAME) or (*:NAME)
- A name is always required with this verb. For all the other backtrack-
+ A name is always required with this verb. For all the other backtrack-
ing control verbs, a NAME argument is optional.
- When a match succeeds, the name of the last-encountered mark name on
+ When a match succeeds, the name of the last-encountered mark name on
the matching path is passed back to the caller as described in the sec-
tion entitled "Other information about the match" in the pcre2api docu-
- mentation. This applies to all instances of (*MARK) and other verbs,
+ mentation. This applies to all instances of (*MARK) and other verbs,
including those inside assertions and atomic groups. However, there are
- differences in those cases when (*MARK) is used in conjunction with
+ differences in those cases when (*MARK) is used in conjunction with
(*SKIP) as described below.
- The mark name that was last encountered on the matching path is passed
- back. A verb without a NAME argument is ignored for this purpose. Here
- is an example of pcre2test output, where the "mark" modifier requests
+ The mark name that was last encountered on the matching path is passed
+ back. A verb without a NAME argument is ignored for this purpose. Here
+ is an example of pcre2test output, where the "mark" modifier requests
the retrieval and outputting of (*MARK) data:
re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
@@ -9099,16 +9162,16 @@
MK: B
The (*MARK) name is tagged with "MK:" in this output, and in this exam-
- ple it indicates which of the two alternatives matched. This is a more
- efficient way of obtaining this information than putting each alterna-
+ ple it indicates which of the two alternatives matched. This is a more
+ efficient way of obtaining this information than putting each alterna-
tive in its own capturing parentheses.
- If a verb with a name is encountered in a positive assertion that is
- true, the name is recorded and passed back if it is the last-encoun-
+ If a verb with a name is encountered in a positive assertion that is
+ true, the name is recorded and passed back if it is the last-encoun-
tered. This does not happen for negative assertions or failing positive
assertions.
- After a partial match or a failed match, the last encountered name in
+ After a partial match or a failed match, the last encountered name in
the entire match process is returned. For example:
re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
@@ -9115,38 +9178,38 @@
data> XP
No match, mark = B
- Note that in this unanchored example the mark is retained from the
+ Note that in this unanchored example the mark is retained from the
match attempt that started at the letter "X" in the subject. Subsequent
match attempts starting at "P" and then with an empty string do not get
as far as the (*MARK) item, but nevertheless do not reset it.
- If you are interested in (*MARK) values after failed matches, you
- should probably set the PCRE2_NO_START_OPTIMIZE option (see above) to
+ If you are interested in (*MARK) values after failed matches, you
+ should probably set the PCRE2_NO_START_OPTIMIZE option (see above) to
ensure that the match is always attempted.
Verbs that act after backtracking
The following verbs do nothing when they are encountered. Matching con-
- tinues with what follows, but if there is a subsequent match failure,
- causing a backtrack to the verb, a failure is forced. That is, back-
- tracking cannot pass to the left of the verb. However, when one of
+ tinues with what follows, but if there is a subsequent match failure,
+ causing a backtrack to the verb, a failure is forced. That is, back-
+ tracking cannot pass to the left of the verb. However, when one of
these verbs appears inside an atomic group or in a lookaround assertion
- that is true, its effect is confined to that group, because once the
- group has been matched, there is never any backtracking into it. Back-
+ that is true, its effect is confined to that group, because once the
+ group has been matched, there is never any backtracking into it. Back-
tracking from beyond an assertion or an atomic group ignores the entire
group, and seeks a preceding backtracking point.
- These verbs differ in exactly what kind of failure occurs when back-
- tracking reaches them. The behaviour described below is what happens
- when the verb is not in a subroutine or an assertion. Subsequent sec-
+ These verbs differ in exactly what kind of failure occurs when back-
+ tracking reaches them. The behaviour described below is what happens
+ when the verb is not in a subroutine or an assertion. Subsequent sec-
tions cover these special cases.
(*COMMIT) or (*COMMIT:NAME)
- This verb causes the whole match to fail outright if there is a later
+ This verb causes the whole match to fail outright if there is a later
matching failure that causes backtracking to reach it. Even if the pat-
- tern is unanchored, no further attempts to find a match by advancing
- the starting point take place. If (*COMMIT) is the only backtracking
+ tern is unanchored, no further attempts to find a match by advancing
+ the starting point take place. If (*COMMIT) is the only backtracking
verb that is encountered, once it has been passed pcre2_match() is com-
mitted to finding a match at the current starting point, or not at all.
For example:
@@ -9153,22 +9216,22 @@
a+(*COMMIT)b
- This matches "xxaab" but not "aacaab". It can be thought of as a kind
+ This matches "xxaab" but not "aacaab". It can be thought of as a kind
of dynamic anchor, or "I've started, so I must finish."
- The behaviour of (*COMMIT:NAME) is not the same as (*MARK:NAME)(*COM-
- MIT). It is like (*MARK:NAME) in that the name is remembered for pass-
- ing back to the caller. However, (*SKIP:NAME) searches only for names
+ The behaviour of (*COMMIT:NAME) is not the same as (*MARK:NAME)(*COM-
+ MIT). It is like (*MARK:NAME) in that the name is remembered for pass-
+ ing back to the caller. However, (*SKIP:NAME) searches only for names
that are set with (*MARK), ignoring those set by any of the other back-
tracking verbs.
- If there is more than one backtracking verb in a pattern, a different
- one that follows (*COMMIT) may be triggered first, so merely passing
+ If there is more than one backtracking verb in a pattern, a different
+ one that follows (*COMMIT) may be triggered first, so merely passing
(*COMMIT) during a match does not always guarantee that a match must be
at this starting point.
Note that (*COMMIT) at the start of a pattern is not the same as an an-
- chor, unless PCRE2's start-of-match optimizations are turned off, as
+ chor, unless PCRE2's start-of-match optimizations are turned off, as
shown in this output from pcre2test:
re> /(*COMMIT)abc/
@@ -9179,68 +9242,68 @@
data> xyzabc
No match
- For the first pattern, PCRE2 knows that any match must start with "a",
- so the optimization skips along the subject to "a" before applying the
- pattern to the first set of data. The match attempt then succeeds. The
- second pattern disables the optimization that skips along to the first
- character. The pattern is now applied starting at "x", and so the
- (*COMMIT) causes the match to fail without trying any other starting
+ For the first pattern, PCRE2 knows that any match must start with "a",
+ so the optimization skips along the subject to "a" before applying the
+ pattern to the first set of data. The match attempt then succeeds. The
+ second pattern disables the optimization that skips along to the first
+ character. The pattern is now applied starting at "x", and so the
+ (*COMMIT) causes the match to fail without trying any other starting
points.
(*PRUNE) or (*PRUNE:NAME)
- This verb causes the match to fail at the current starting position in
+ This verb causes the match to fail at the current starting position in
the subject if there is a later matching failure that causes backtrack-
- ing to reach it. If the pattern is unanchored, the normal "bumpalong"
- advance to the next starting character then happens. Backtracking can
- occur as usual to the left of (*PRUNE), before it is reached, or when
- matching to the right of (*PRUNE), but if there is no match to the
- right, backtracking cannot cross (*PRUNE). In simple cases, the use of
- (*PRUNE) is just an alternative to an atomic group or possessive quan-
+ ing to reach it. If the pattern is unanchored, the normal "bumpalong"
+ advance to the next starting character then happens. Backtracking can
+ occur as usual to the left of (*PRUNE), before it is reached, or when
+ matching to the right of (*PRUNE), but if there is no match to the
+ right, backtracking cannot cross (*PRUNE). In simple cases, the use of
+ (*PRUNE) is just an alternative to an atomic group or possessive quan-
tifier, but there are some uses of (*PRUNE) that cannot be expressed in
- any other way. In an anchored pattern (*PRUNE) has the same effect as
+ any other way. In an anchored pattern (*PRUNE) has the same effect as
(*COMMIT).
The behaviour of (*PRUNE:NAME) is not the same as (*MARK:NAME)(*PRUNE).
It is like (*MARK:NAME) in that the name is remembered for passing back
- to the caller. However, (*SKIP:NAME) searches only for names set with
+ to the caller. However, (*SKIP:NAME) searches only for names set with
(*MARK), ignoring those set by other backtracking verbs.
(*SKIP)
- This verb, when given without a name, is like (*PRUNE), except that if
- the pattern is unanchored, the "bumpalong" advance is not to the next
+ This verb, when given without a name, is like (*PRUNE), except that if
+ the pattern is unanchored, the "bumpalong" advance is not to the next
character, but to the position in the subject where (*SKIP) was encoun-
- tered. (*SKIP) signifies that whatever text was matched leading up to
- it cannot be part of a successful match if there is a later mismatch.
+ tered. (*SKIP) signifies that whatever text was matched leading up to
+ it cannot be part of a successful match if there is a later mismatch.
Consider:
a+(*SKIP)b
- If the subject is "aaaac...", after the first match attempt fails
- (starting at the first character in the string), the starting point
+ If the subject is "aaaac...", after the first match attempt fails
+ (starting at the first character in the string), the starting point
skips on to start the next attempt at "c". Note that a possessive quan-
- tifer does not have the same effect as this example; although it would
- suppress backtracking during the first match attempt, the second at-
- tempt would start at the second character instead of skipping on to
+ tifer does not have the same effect as this example; although it would
+ suppress backtracking during the first match attempt, the second at-
+ tempt would start at the second character instead of skipping on to
"c".
- If (*SKIP) is used to specify a new starting position that is the same
- as the starting position of the current match, or (by being inside a
- lookbehind) earlier, the position specified by (*SKIP) is ignored, and
+ If (*SKIP) is used to specify a new starting position that is the same
+ as the starting position of the current match, or (by being inside a
+ lookbehind) earlier, the position specified by (*SKIP) is ignored, and
instead the normal "bumpalong" occurs.
(*SKIP:NAME)
- When (*SKIP) has an associated name, its behaviour is modified. When
- such a (*SKIP) is triggered, the previous path through the pattern is
- searched for the most recent (*MARK) that has the same name. If one is
- found, the "bumpalong" advance is to the subject position that corre-
- sponds to that (*MARK) instead of to where (*SKIP) was encountered. If
+ When (*SKIP) has an associated name, its behaviour is modified. When
+ such a (*SKIP) is triggered, the previous path through the pattern is
+ searched for the most recent (*MARK) that has the same name. If one is
+ found, the "bumpalong" advance is to the subject position that corre-
+ sponds to that (*MARK) instead of to where (*SKIP) was encountered. If
no (*MARK) with a matching name is found, the (*SKIP) is ignored.
- The search for a (*MARK) name uses the normal backtracking mechanism,
- which means that it does not see (*MARK) settings that are inside
+ The search for a (*MARK) name uses the normal backtracking mechanism,
+ which means that it does not see (*MARK) settings that are inside
atomic groups or assertions, because they are never re-entered by back-
tracking. Compare the following pcre2test examples:
@@ -9254,105 +9317,105 @@
0: b
1: b
- In the first example, the (*MARK) setting is in an atomic group, so it
+ In the first example, the (*MARK) setting is in an atomic group, so it
is not seen when (*SKIP:X) triggers, causing the (*SKIP) to be ignored.
- This allows the second branch of the pattern to be tried at the first
- character position. In the second example, the (*MARK) setting is not
- in an atomic group. This allows (*SKIP:X) to find the (*MARK) when it
+ This allows the second branch of the pattern to be tried at the first
+ character position. In the second example, the (*MARK) setting is not
+ in an atomic group. This allows (*SKIP:X) to find the (*MARK) when it
backtracks, and this causes a new matching attempt to start at the sec-
- ond character. This time, the (*MARK) is never seen because "a" does
+ ond character. This time, the (*MARK) is never seen because "a" does
not match "b", so the matcher immediately jumps to the second branch of
the pattern.
- Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It
+ Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It
ignores names that are set by other backtracking verbs.
(*THEN) or (*THEN:NAME)
- This verb causes a skip to the next innermost alternative when back-
- tracking reaches it. That is, it cancels any further backtracking
- within the current alternative. Its name comes from the observation
+ This verb causes a skip to the next innermost alternative when back-
+ tracking reaches it. That is, it cancels any further backtracking
+ within the current alternative. Its name comes from the observation
that it can be used for a pattern-based if-then-else block:
( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
- If the COND1 pattern matches, FOO is tried (and possibly further items
- after the end of the group if FOO succeeds); on failure, the matcher
- skips to the second alternative and tries COND2, without backtracking
- into COND1. If that succeeds and BAR fails, COND3 is tried. If subse-
- quently BAZ fails, there are no more alternatives, so there is a back-
- track to whatever came before the entire group. If (*THEN) is not in-
+ If the COND1 pattern matches, FOO is tried (and possibly further items
+ after the end of the group if FOO succeeds); on failure, the matcher
+ skips to the second alternative and tries COND2, without backtracking
+ into COND1. If that succeeds and BAR fails, COND3 is tried. If subse-
+ quently BAZ fails, there are no more alternatives, so there is a back-
+ track to whatever came before the entire group. If (*THEN) is not in-
side an alternation, it acts like (*PRUNE).
- The behaviour of (*THEN:NAME) is not the same as (*MARK:NAME)(*THEN).
+ The behaviour of (*THEN:NAME) is not the same as (*MARK:NAME)(*THEN).
It is like (*MARK:NAME) in that the name is remembered for passing back
- to the caller. However, (*SKIP:NAME) searches only for names set with
+ to the caller. However, (*SKIP:NAME) searches only for names set with
(*MARK), ignoring those set by other backtracking verbs.
- A group that does not contain a | character is just a part of the en-
- closing alternative; it is not a nested alternation with only one al-
+ A group that does not contain a | character is just a part of the en-
+ closing alternative; it is not a nested alternation with only one al-
ternative. The effect of (*THEN) extends beyond such a group to the en-
- closing alternative. Consider this pattern, where A, B, etc. are com-
- plex pattern fragments that do not contain any | characters at this
+ closing alternative. Consider this pattern, where A, B, etc. are com-
+ plex pattern fragments that do not contain any | characters at this
level:
A (B(*THEN)C) | D
- If A and B are matched, but there is a failure in C, matching does not
+ If A and B are matched, but there is a failure in C, matching does not
backtrack into A; instead it moves to the next alternative, that is, D.
- However, if the group containing (*THEN) is given an alternative, it
+ However, if the group containing (*THEN) is given an alternative, it
behaves differently:
A (B(*THEN)C | (*FAIL)) | D
The effect of (*THEN) is now confined to the inner group. After a fail-
- ure in C, matching moves to (*FAIL), which causes the whole group to
- fail because there are no more alternatives to try. In this case,
+ ure in C, matching moves to (*FAIL), which causes the whole group to
+ fail because there are no more alternatives to try. In this case,
matching does backtrack into A.
- Note that a conditional group is not considered as having two alterna-
- tives, because only one is ever used. In other words, the | character
- in a conditional group has a different meaning. Ignoring white space,
+ Note that a conditional group is not considered as having two alterna-
+ tives, because only one is ever used. In other words, the | character
+ in a conditional group has a different meaning. Ignoring white space,
consider:
^.*? (?(?=a) a | b(*THEN)c )
If the subject is "ba", this pattern does not match. Because .*? is un-
- greedy, it initially matches zero characters. The condition (?=a) then
- fails, the character "b" is matched, but "c" is not. At this point,
- matching does not backtrack to .*? as might perhaps be expected from
- the presence of the | character. The conditional group is part of the
- single alternative that comprises the whole pattern, and so the match
- fails. (If there was a backtrack into .*?, allowing it to match "b",
+ greedy, it initially matches zero characters. The condition (?=a) then
+ fails, the character "b" is matched, but "c" is not. At this point,
+ matching does not backtrack to .*? as might perhaps be expected from
+ the presence of the | character. The conditional group is part of the
+ single alternative that comprises the whole pattern, and so the match
+ fails. (If there was a backtrack into .*?, allowing it to match "b",
the match would succeed.)
- The verbs just described provide four different "strengths" of control
+ The verbs just described provide four different "strengths" of control
when subsequent matching fails. (*THEN) is the weakest, carrying on the
- match at the next alternative. (*PRUNE) comes next, failing the match
- at the current starting position, but allowing an advance to the next
- character (for an unanchored pattern). (*SKIP) is similar, except that
+ match at the next alternative. (*PRUNE) comes next, failing the match
+ at the current starting position, but allowing an advance to the next
+ character (for an unanchored pattern). (*SKIP) is similar, except that
the advance may be more than one character. (*COMMIT) is the strongest,
causing the entire match to fail.
More than one backtracking verb
- If more than one backtracking verb is present in a pattern, the one
- that is backtracked onto first acts. For example, consider this pat-
+ If more than one backtracking verb is present in a pattern, the one
+ that is backtracked onto first acts. For example, consider this pat-
tern, where A, B, etc. are complex pattern fragments:
(A(*COMMIT)B(*THEN)C|ABD)
- If A matches but B fails, the backtrack to (*COMMIT) causes the entire
+ If A matches but B fails, the backtrack to (*COMMIT) causes the entire
match to fail. However, if A and B match, but C fails, the backtrack to
- (*THEN) causes the next alternative (ABD) to be tried. This behaviour
- is consistent, but is not always the same as Perl's. It means that if
- two or more backtracking verbs appear in succession, all the the last
+ (*THEN) causes the next alternative (ABD) to be tried. This behaviour
+ is consistent, but is not always the same as Perl's. It means that if
+ two or more backtracking verbs appear in succession, all the the last
of them has no effect. Consider this example:
...(*COMMIT)(*PRUNE)...
If there is a matching failure to the right, backtracking onto (*PRUNE)
- causes it to be triggered, and its action is taken. There can never be
+ causes it to be triggered, and its action is taken. There can never be
a backtrack onto (*COMMIT).
Backtracking verbs in repeated groups
@@ -9362,42 +9425,42 @@
/(a(*COMMIT)b)+ac/
- If the subject is "abac", Perl matches unless its optimizations are
- disabled, but PCRE2 always fails because the (*COMMIT) in the second
+ If the subject is "abac", Perl matches unless its optimizations are
+ disabled, but PCRE2 always fails because the (*COMMIT) in the second
repeat of the group acts.
Backtracking verbs in assertions
- (*FAIL) in any assertion has its normal effect: it forces an immediate
- backtrack. The behaviour of the other backtracking verbs depends on
- whether or not the assertion is standalone or acting as the condition
+ (*FAIL) in any assertion has its normal effect: it forces an immediate
+ backtrack. The behaviour of the other backtracking verbs depends on
+ whether or not the assertion is standalone or acting as the condition
in a conditional group.
- (*ACCEPT) in a standalone positive assertion causes the assertion to
- succeed without any further processing; captured strings and a mark
- name (if set) are retained. In a standalone negative assertion, (*AC-
+ (*ACCEPT) in a standalone positive assertion causes the assertion to
+ succeed without any further processing; captured strings and a mark
+ name (if set) are retained. In a standalone negative assertion, (*AC-
CEPT) causes the assertion to fail without any further processing; cap-
tured substrings and any mark name are discarded.
- If the assertion is a condition, (*ACCEPT) causes the condition to be
- true for a positive assertion and false for a negative one; captured
+ If the assertion is a condition, (*ACCEPT) causes the condition to be
+ true for a positive assertion and false for a negative one; captured
substrings are retained in both cases.
The remaining verbs act only when a later failure causes a backtrack to
- reach them. This means that their effect is confined to the assertion,
+ reach them. This means that their effect is confined to the assertion,
because lookaround assertions are atomic. A backtrack that occurs after
an assertion is complete does not jump back into the assertion. Note in
- particular that a (*MARK) name that is set in an assertion is not
+ particular that a (*MARK) name that is set in an assertion is not
"seen" by an instance of (*SKIP:NAME) latter in the pattern.
- The effect of (*THEN) is not allowed to escape beyond an assertion. If
- there are no more branches to try, (*THEN) causes a positive assertion
+ The effect of (*THEN) is not allowed to escape beyond an assertion. If
+ there are no more branches to try, (*THEN) causes a positive assertion
to be false, and a negative assertion to be true.
- The other backtracking verbs are not treated specially if they appear
- in a standalone positive assertion. In a conditional positive asser-
+ The other backtracking verbs are not treated specially if they appear
+ in a standalone positive assertion. In a conditional positive asser-
tion, backtracking (from within the assertion) into (*COMMIT), (*SKIP),
- or (*PRUNE) causes the condition to be false. However, for both stand-
+ or (*PRUNE) causes the condition to be false. However, for both stand-
alone and conditional negative assertions, backtracking into (*COMMIT),
(*SKIP), or (*PRUNE) causes the assertion to be true, without consider-
ing any further alternative branches.
@@ -9407,19 +9470,19 @@
These behaviours occur whether or not the group is called recursively.
(*ACCEPT) in a group called as a subroutine causes the subroutine match
- to succeed without any further processing. Matching then continues af-
- ter the subroutine call. Perl documents this behaviour. Perl's treat-
+ to succeed without any further processing. Matching then continues af-
+ ter the subroutine call. Perl documents this behaviour. Perl's treat-
ment of the other verbs in subroutines is different in some cases.
- (*FAIL) in a group called as a subroutine has its normal effect: it
+ (*FAIL) in a group called as a subroutine has its normal effect: it
forces an immediate backtrack.
- (*COMMIT), (*SKIP), and (*PRUNE) cause the subroutine match to fail
- when triggered by being backtracked to in a group called as a subrou-
+ (*COMMIT), (*SKIP), and (*PRUNE) cause the subroutine match to fail
+ when triggered by being backtracked to in a group called as a subrou-
tine. There is then a backtrack at the outer level.
(*THEN), when triggered, skips to the next alternative in the innermost
- enclosing group that has alternatives (its normal behaviour). However,
+ enclosing group that has alternatives (its normal behaviour). However,
if there is no such group within the subroutine's group, the subroutine
match fails and there is a backtrack at the outer level.
@@ -9426,7 +9489,7 @@
SEE ALSO
- pcre2api(3), pcre2callout(3), pcre2matching(3), pcre2syntax(3),
+ pcre2api(3), pcre2callout(3), pcre2matching(3), pcre2syntax(3),
pcre2(3).
@@ -9439,7 +9502,7 @@
REVISION
- Last updated: 22 June 2019
+ Last updated: 13 July 2019
Copyright (c) 1997-2019 University of Cambridge.
------------------------------------------------------------------------------
@@ -10663,6 +10726,17 @@
Each top-level branch of a lookbehind must be of a fixed length.
+NON-ATOMIC LOOKAROUND ASSERTIONS
+
+ These assertions are specific to PCRE2 and are not Perl-compatible.
+
+ (*napla:...)
+ (*non_atomic_positive_lookahead:...)
+
+ (*naplb:...)
+ (*non_atomic_positive_lookbehind:...)
+
+
SCRIPT RUNS
(*script_run:...) ) script run, can be backtracked into
@@ -10784,7 +10858,7 @@
REVISION
- Last updated: 11 February 2019
+ Last updated: 12 July 2019
Copyright (c) 1997-2019 University of Cambridge.
------------------------------------------------------------------------------
Modified: code/trunk/doc/pcre2compat.3
===================================================================
--- code/trunk/doc/pcre2compat.3 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/doc/pcre2compat.3 2019-07-13 11:12:03 UTC (rev 1130)
@@ -1,4 +1,4 @@
-.TH PCRE2COMPAT 3 "12 February 2019" "PCRE2 10.33"
+.TH PCRE2COMPAT 3 "13 July 2019" "PCRE2 10.34"
.SH NAME
PCRE2 - Perl-compatible regular expressions (revised API)
.SH "DIFFERENCES BETWEEN PCRE2 AND PERL"
@@ -170,6 +170,10 @@
(l) PCRE2 recognizes some special sequences such as (*CR) or (*NO_JIT) at
the start of a pattern that set overall options that cannot be changed within
the pattern.
+.sp
+(m) PCRE2 supports non-atomic positive lookaround assertions. This is an
+extension to the lookaround facilities. The default, Perl-compatible
+lookarounds are atomic.
.P
18. The Perl /a modifier restricts /d numbers to pure ascii, and the /aa
modifier restricts /i case-insensitive matching to pure ascii, ignoring Unicode
@@ -199,6 +203,6 @@
.rs
.sp
.nf
-Last updated: 12 February 2019
+Last updated: 13 July 2019
Copyright (c) 1997-2019 University of Cambridge.
.fi
Modified: code/trunk/doc/pcre2pattern.3
===================================================================
--- code/trunk/doc/pcre2pattern.3 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/doc/pcre2pattern.3 2019-07-13 11:12:03 UTC (rev 1130)
@@ -1,4 +1,4 @@
-.TH PCRE2PATTERN 3 "22 June 2019" "PCRE2 10.34"
+.TH PCRE2PATTERN 3 "13 July 2019" "PCRE2 10.34"
.SH NAME
PCRE2 - Perl-compatible regular expressions (revised API)
.SH "PCRE2 REGULAR EXPRESSION DETAILS"
@@ -2370,9 +2370,19 @@
match for the assertion to be true) or negative (must not match for the
assertion to be true). An assertion group is matched in the normal way,
and if it is true, matching continues after it, but with the matching position
-in the subject string is was it was before the assertion was processed.
+in the subject string reset to what it was before the assertion was processed.
.P
-A lookaround assertion may also appear as the condition in a
+The Perl-compatible lookaround assertions are atomic. If an assertion is true,
+but there is a subsequent matching failure, there is no backtracking into the
+assertion. However, there are some cases where non-atomic assertions can be
+useful. PCRE2 has some support for these, described in the section entitled
+.\" HTML <a href="#nonatomicassertions">
+.\" </a>
+"Non-atomic assertions"
+.\"
+below, but they are not Perl-compatible.
+.P
+A lookaround assertion may appear as the condition in a
.\" HTML <a href="#conditions">
.\" </a>
conditional group
@@ -2380,9 +2390,6 @@
(see below). In this case, the result of matching the assertion determines
which branch of the condition is followed.
.P
-Lookaround assertions are atomic. If an assertion is true, but there is a
-subsequent matching failure, there is no backtracking into the assertion.
-.P
Assertion groups are not capture groups. If an assertion contains capture
groups within it, these are counted for the purposes of numbering the capture
groups in the whole pattern. Within each branch of an assertion, locally
@@ -2435,11 +2442,11 @@
.SS "Alphabetic assertion names"
.rs
.sp
-Traditionally, symbolic sequences such as (?= and (?<= have been used to specify
-lookaround assertions. Perl 5.28 introduced some experimental alphabetic
-alternatives which might be easier to remember. They all start with (* instead
-of (? and must be written using lower case letters. PCRE2 supports the
-following synonyms:
+Traditionally, symbolic sequences such as (?= and (?<= have been used to
+specify lookaround assertions. Perl 5.28 introduced some experimental
+alphabetic alternatives which might be easier to remember. They all start with
+(* instead of (? and must be written using lower case letters. PCRE2 supports
+the following synonyms:
.sp
(*positive_lookahead: or (*pla: is the same as (?=
(*negative_lookahead: or (*nla: is the same as (?!
@@ -2616,6 +2623,63 @@
characters that are not "999".
.
.
+.\" HTML <a name="nonatomicassertions"></a>
+.SH "NON-ATOMIC ASSERTIONS"
+.rs
+.sp
+The traditional Perl-compatible lookaround assertions are atomic. That is, if
+an assertion is true, but there is a subsequent matching failure, there is no
+backtracking into the assertion. However, there are some cases where non-atomic
+positive assertions can be useful. PCRE2 provides these using the following
+syntax:
+.sp
+ (*non_atomic_positive_lookahead: or (*napla:
+ (*non_atomic_positive_lookbehind: or (*naplb:
+.sp
+Consider the problem of finding the right-most word in a string that also
+appears earlier in the string, that is, it must appear at least twice in total.
+This pattern returns the required result as captured substring 1:
+.sp
+ ^(?x)(*napla: .* \eb(\ew++)) (?> .*? \eb\e1\eb ){2}
+.sp
+For a subject such as "word1 word2 word3 word2 word3 word4" the result is
+"word3". How does it work? At the start, ^(?x) anchors the pattern and sets the
+"x" option, which causes white space (introduced for readability) to be
+ignored. Inside the assertion, the greedy .* at first consumes the entire
+string, but then has to backtrack until the rest of the assertion can match a
+word, which is captured by group 1. In other words, when the assertion first
+succeeds, it captures the right-most word in the string.
+.P
+The current matching point is then reset to the start of the subject, and the
+rest of the pattern match checks for two occurrences of the captured word,
+using an ungreedy .*? to scan from the left. If this succeeds, we are done, but
+if the last word in the string does not occur twice, this part of the pattern
+fails. If a traditional atomic lookhead (?= or (*pla: had been used, the
+assertion could not be re-entered, and the whole match would fail. The pattern
+would succeed only if the very last word in the subject was found twice.
+.P
+Using a non-atomic lookahead, however, means that when the last word does not
+occur twice in the string, the lookahead can backtrack and find the second-last
+word, and so on, until either the match succeeds, or all words have been
+tested.
+.P
+Two conditions must be met for a non-atomic assertion to be useful: the
+contents of one or more capturing groups must change after a backtrack into the
+assertion, and there must be a backreference to a changed group later in the
+pattern. If this is not the case, the rest of the pattern match fails exactly
+as before because nothing has changed, so using a non-atomic assertion just
+wastes resources.
+.P
+Non-atomic assertions are not supported by the alternative matching function
+\fBpcre2_dfa_match()\fP. They are also not supported by JIT (but may be in
+future). Note that assertions that appear as conditions for
+.\" HTML <a href="#conditions">
+.\" </a>
+conditional groups
+.\"
+(see below) must be atomic.
+.
+.
.SH "SCRIPT RUNS"
.rs
.sp
@@ -2867,8 +2931,15 @@
.sp
If the condition is not in any of the above formats, it must be a parenthesized
assertion. This may be a positive or negative lookahead or lookbehind
-assertion. Consider this pattern, again containing non-significant white space,
-and with the two alternatives on the second line:
+assertion. However, it must be a traditional atomic assertion, not one of the
+PCRE2-specific
+.\" HTML <a href="#nonatomicassertions">
+.\" </a>
+non-atomic assertions.
+.\"
+.P
+Consider this pattern, again containing non-significant white space, and with
+the two alternatives on the second line:
.sp
(?(?=[^a-z]*[a-z])
\ed{2}-[a-z]{3}-\ed{2} | \ed{2}-\ed{2}-\ed{2} )
@@ -3788,6 +3859,6 @@
.rs
.sp
.nf
-Last updated: 22 June 2019
+Last updated: 13 July 2019
Copyright (c) 1997-2019 University of Cambridge.
.fi
Modified: code/trunk/doc/pcre2syntax.3
===================================================================
--- code/trunk/doc/pcre2syntax.3 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/doc/pcre2syntax.3 2019-07-13 11:12:03 UTC (rev 1130)
@@ -1,4 +1,4 @@
-.TH PCRE2SYNTAX 3 "11 February 2019" "PCRE2 10.33"
+.TH PCRE2SYNTAX 3 "12 July 2019" "PCRE2 10.34"
.SH NAME
PCRE2 - Perl-compatible regular expressions (revised API)
.SH "PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY"
@@ -522,6 +522,18 @@
Each top-level branch of a lookbehind must be of a fixed length.
.
.
+.SH "NON-ATOMIC LOOKAROUND ASSERTIONS"
+.rs
+.sp
+These assertions are specific to PCRE2 and are not Perl-compatible.
+.sp
+ (*napla:...)
+ (*non_atomic_positive_lookahead:...)
+.sp
+ (*naplb:...)
+ (*non_atomic_positive_lookbehind:...)
+.
+.
.SH "SCRIPT RUNS"
.rs
.sp
@@ -654,6 +666,6 @@
.rs
.sp
.nf
-Last updated: 11 February 2019
+Last updated: 12 July 2019
Copyright (c) 1997-2019 University of Cambridge.
.fi
Modified: code/trunk/src/pcre2.h.in
===================================================================
--- code/trunk/src/pcre2.h.in 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/src/pcre2.h.in 2019-07-13 11:12:03 UTC (rev 1130)
@@ -307,6 +307,7 @@
#define PCRE2_ERROR_ALPHA_ASSERTION_UNKNOWN 195
#define PCRE2_ERROR_SCRIPT_RUN_NOT_AVAILABLE 196
#define PCRE2_ERROR_TOO_MANY_CAPTURES 197
+#define PCRE2_ERROR_CONDITION_ATOMIC_ASSERTION_EXPECTED 198
/* "Expected" matching error codes: no match and partial match. */
Modified: code/trunk/src/pcre2_auto_possess.c
===================================================================
--- code/trunk/src/pcre2_auto_possess.c 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/src/pcre2_auto_possess.c 2019-07-13 11:12:03 UTC (rev 1130)
@@ -624,6 +624,13 @@
case OP_ASSERTBACK_NOT:
case OP_ONCE:
return !entered_a_group;
+
+ /* Non-atomic assertions - don't possessify last iterator. This needs
+ more thought. */
+
+ case OP_ASSERT_NA:
+ case OP_ASSERTBACK_NA:
+ return FALSE;
}
/* Skip over the bracket and inspect what comes next. */
Modified: code/trunk/src/pcre2_compile.c
===================================================================
--- code/trunk/src/pcre2_compile.c 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/src/pcre2_compile.c 2019-07-13 11:12:03 UTC (rev 1130)
@@ -250,36 +250,41 @@
#define META_LOOKBEHIND 0x80250000u /* (?<= */
#define META_LOOKBEHINDNOT 0x80260000u /* (?<! */
+/* These cannot be conditions */
+
+#define META_LOOKAHEAD_NA 0x80270000u /* (*napla: */
+#define META_LOOKBEHIND_NA 0x80280000u /* (*naplb: */
+
/* These must be kept in this order, with consecutive values, and the _ARG
versions of COMMIT, PRUNE, SKIP, and THEN immediately after their non-argument
versions. */
-#define META_MARK 0x80270000u /* (*MARK) */
-#define META_ACCEPT 0x80280000u /* (*ACCEPT) */
-#define META_FAIL 0x80290000u /* (*FAIL) */
-#define META_COMMIT 0x802a0000u /* These */
-#define META_COMMIT_ARG 0x802b0000u /* pairs */
-#define META_PRUNE 0x802c0000u /* must */
-#define META_PRUNE_ARG 0x802d0000u /* be */
-#define META_SKIP 0x802e0000u /* kept */
-#define META_SKIP_ARG 0x802f0000u /* in */
-#define META_THEN 0x80300000u /* this */
-#define META_THEN_ARG 0x80310000u /* order */
+#define META_MARK 0x80290000u /* (*MARK) */
+#define META_ACCEPT 0x802a0000u /* (*ACCEPT) */
+#define META_FAIL 0x802b0000u /* (*FAIL) */
+#define META_COMMIT 0x802c0000u /* These */
+#define META_COMMIT_ARG 0x802d0000u /* pairs */
+#define META_PRUNE 0x802e0000u /* must */
+#define META_PRUNE_ARG 0x802f0000u /* be */
+#define META_SKIP 0x80300000u /* kept */
+#define META_SKIP_ARG 0x80310000u /* in */
+#define META_THEN 0x80320000u /* this */
+#define META_THEN_ARG 0x80330000u /* order */
/* These must be kept in groups of adjacent 3 values, and all together. */
-#define META_ASTERISK 0x80320000u /* * */
-#define META_ASTERISK_PLUS 0x80330000u /* *+ */
-#define META_ASTERISK_QUERY 0x80340000u /* *? */
-#define META_PLUS 0x80350000u /* + */
-#define META_PLUS_PLUS 0x80360000u /* ++ */
-#define META_PLUS_QUERY 0x80370000u /* +? */
-#define META_QUERY 0x80380000u /* ? */
-#define META_QUERY_PLUS 0x80390000u /* ?+ */
-#define META_QUERY_QUERY 0x803a0000u /* ?? */
-#define META_MINMAX 0x803b0000u /* {n,m} repeat */
-#define META_MINMAX_PLUS 0x803c0000u /* {n,m}+ repeat */
-#define META_MINMAX_QUERY 0x803d0000u /* {n,m}? repeat */
+#define META_ASTERISK 0x80340000u /* * */
+#define META_ASTERISK_PLUS 0x80350000u /* *+ */
+#define META_ASTERISK_QUERY 0x80360000u /* *? */
+#define META_PLUS 0x80370000u /* + */
+#define META_PLUS_PLUS 0x80380000u /* ++ */
+#define META_PLUS_QUERY 0x80390000u /* +? */
+#define META_QUERY 0x803a0000u /* ? */
+#define META_QUERY_PLUS 0x803b0000u /* ?+ */
+#define META_QUERY_QUERY 0x803c0000u /* ?? */
+#define META_MINMAX 0x803d0000u /* {n,m} repeat */
+#define META_MINMAX_PLUS 0x803e0000u /* {n,m}+ repeat */
+#define META_MINMAX_QUERY 0x803f0000u /* {n,m}? repeat */
#define META_FIRST_QUANTIFIER META_ASTERISK
#define META_LAST_QUANTIFIER META_MINMAX_QUERY
@@ -335,6 +340,8 @@
0, /* META_LOOKAHEADNOT */
SIZEOFFSET, /* META_LOOKBEHIND */
SIZEOFFSET, /* META_LOOKBEHINDNOT */
+ 0, /* META_LOOKAHEAD_NA */
+ SIZEOFFSET, /* META_LOOKBEHIND_NA */
1, /* META_MARK - plus the string length */
0, /* META_ACCEPT */
0, /* META_FAIL */
@@ -637,10 +644,14 @@
static const char alasnames[] =
STRING_pla0
STRING_plb0
+ STRING_napla0
+ STRING_naplb0
STRING_nla0
STRING_nlb0
STRING_positive_lookahead0
STRING_positive_lookbehind0
+ STRING_non_atomic_positive_lookahead0
+ STRING_non_atomic_positive_lookbehind0
STRING_negative_lookahead0
STRING_negative_lookbehind0
STRING_atomic0
@@ -652,10 +663,14 @@
static const alasitem alasmeta[] = {
{ 3, META_LOOKAHEAD },
{ 3, META_LOOKBEHIND },
+ { 5, META_LOOKAHEAD_NA },
+ { 5, META_LOOKBEHIND_NA },
{ 3, META_LOOKAHEADNOT },
{ 3, META_LOOKBEHINDNOT },
{ 18, META_LOOKAHEAD },
{ 19, META_LOOKBEHIND },
+ { 29, META_LOOKAHEAD_NA },
+ { 30, META_LOOKBEHIND_NA },
{ 18, META_LOOKAHEADNOT },
{ 19, META_LOOKBEHINDNOT },
{ 6, META_ATOMIC },
@@ -784,7 +799,7 @@
ERR61, ERR62, ERR63, ERR64, ERR65, ERR66, ERR67, ERR68, ERR69, ERR70,
ERR71, ERR72, ERR73, ERR74, ERR75, ERR76, ERR77, ERR78, ERR79, ERR80,
ERR81, ERR82, ERR83, ERR84, ERR85, ERR86, ERR87, ERR88, ERR89, ERR90,
- ERR91, ERR92, ERR93, ERR94, ERR95, ERR96, ERR97 };
+ ERR91, ERR92, ERR93, ERR94, ERR95, ERR96, ERR97, ERR98 };
/* This is a table of start-of-pattern options such as (*UTF) and settings such
as (*LIMIT_MATCH=nnnn) and (*CRLF). For completeness and backward
@@ -1015,6 +1030,7 @@
case META_NOCAPTURE: fprintf(stderr, "META (?:"); break;
case META_LOOKAHEAD: fprintf(stderr, "META (?="); break;
case META_LOOKAHEADNOT: fprintf(stderr, "META (?!"); break;
+ case META_LOOKAHEAD_NA: fprintf(stderr, "META (*napla:"); break;
case META_SCRIPT_RUN: fprintf(stderr, "META (*sr:"); break;
case META_KET: fprintf(stderr, "META )"); break;
case META_ALT: fprintf(stderr, "META | %d", meta_arg); break;
@@ -1046,6 +1062,12 @@
fprintf(stderr, "%zd", offset);
break;
+ case META_LOOKBEHIND_NA:
+ fprintf(stderr, "META (*naplb: %d offset=", meta_arg);
+ GETOFFSET(offset, pptr);
+ fprintf(stderr, "%zd", offset);
+ break;
+
case META_LOOKBEHINDNOT:
fprintf(stderr, "META (?<! %d offset=", meta_arg);
GETOFFSET(offset, pptr);
@@ -3695,19 +3717,20 @@
goto FAILED;
}
- /* Check for expecting an assertion condition. If so, only lookaround
- assertions are valid. */
+ /* Check for expecting an assertion condition. If so, only atomic
+ lookaround assertions are valid. */
meta = alasmeta[i].meta;
if (prev_expect_cond_assert > 0 &&
(meta < META_LOOKAHEAD || meta > META_LOOKBEHINDNOT))
{
- errorcode = ERR28; /* Assertion expected */
+ errorcode = (meta == META_LOOKAHEAD_NA || meta == META_LOOKBEHIND_NA)?
+ ERR98 : ERR28; /* (Atomic) assertion expected */
goto FAILED;
}
- /* The lookaround alphabetic synonyms can be almost entirely handled by
- jumping to the code that handles the traditional symbolic forms. */
+ /* The lookaround alphabetic synonyms can mostly be handled by jumping
+ to the code that handles the traditional symbolic forms. */
switch(meta)
{
@@ -3721,11 +3744,17 @@
case META_LOOKAHEAD:
goto POSITIVE_LOOK_AHEAD;
+ case META_LOOKAHEAD_NA:
+ *parsed_pattern++ = meta;
+ ptr++;
+ goto POST_ASSERTION;
+
case META_LOOKAHEADNOT:
goto NEGATIVE_LOOK_AHEAD;
case META_LOOKBEHIND:
case META_LOOKBEHINDNOT:
+ case META_LOOKBEHIND_NA:
*parsed_pattern++ = meta;
ptr--;
goto POST_LOOKBEHIND;
@@ -4429,7 +4458,7 @@
*parsed_pattern++ = (ptr[1] == CHAR_EQUALS_SIGN)?
META_LOOKBEHIND : META_LOOKBEHINDNOT;
- POST_LOOKBEHIND: /* Come from (*plb: and (*nlb: */
+ POST_LOOKBEHIND: /* Come from (*plb: (*naplb: and (*nlb: */
*has_lookbehind = TRUE;
offset = (PCRE2_SIZE)(ptr - cb->start_pattern - 2);
PUTOFFSET(offset, parsed_pattern);
@@ -6300,6 +6329,11 @@
cb->assert_depth += 1;
goto GROUP_PROCESS;
+ case META_LOOKAHEAD_NA:
+ bravalue = OP_ASSERT_NA;
+ cb->assert_depth += 1;
+ goto GROUP_PROCESS;
+
/* Optimize (?!) to (*FAIL) unless it is quantified - which is a weird
thing to do, but Perl allows all assertions to be quantified, and when
they contain capturing parentheses there may be a potential use for
@@ -6331,6 +6365,11 @@
cb->assert_depth += 1;
goto GROUP_PROCESS;
+ case META_LOOKBEHIND_NA:
+ bravalue = OP_ASSERTBACK_NA;
+ cb->assert_depth += 1;
+ goto GROUP_PROCESS;
+
case META_ATOMIC:
bravalue = OP_ONCE;
goto GROUP_PROCESS_NOTE_EMPTY;
@@ -7931,7 +7970,10 @@
/* Remember if this is a lookbehind assertion, and if it is, save its length
and skip over the pattern offset. */
-lookbehind = *code == OP_ASSERTBACK || *code == OP_ASSERTBACK_NOT;
+lookbehind = *code == OP_ASSERTBACK ||
+ *code == OP_ASSERTBACK_NOT ||
+ *code == OP_ASSERTBACK_NA;
+
if (lookbehind)
{
lookbehindlength = META_DATA(pptr[-1]);
@@ -8802,8 +8844,10 @@
case META_COND_VERSION:
case META_LOOKAHEAD:
case META_LOOKAHEADNOT:
+ case META_LOOKAHEAD_NA:
case META_LOOKBEHIND:
case META_LOOKBEHINDNOT:
+ case META_LOOKBEHIND_NA:
case META_NOCAPTURE:
case META_SCRIPT_RUN:
nestlevel++;
@@ -9064,6 +9108,7 @@
case META_LOOKAHEAD:
case META_LOOKAHEADNOT:
+ case META_LOOKAHEAD_NA:
pptr = parsed_skip(pptr + 1, PSKIP_KET);
if (pptr == NULL) goto PARSED_SKIP_FAILED;
@@ -9102,6 +9147,7 @@
case META_LOOKBEHIND:
case META_LOOKBEHINDNOT:
+ case META_LOOKBEHIND_NA:
if (!set_lookbehind_lengths(&pptr, &max, errcodeptr, lcptr, recurses, cb))
return -1;
if (max - branchlength > extra) extra = max - branchlength;
@@ -9453,6 +9499,7 @@
case META_KET:
case META_LOOKAHEAD:
case META_LOOKAHEADNOT:
+ case META_LOOKAHEAD_NA:
case META_NOCAPTURE:
case META_PLUS:
case META_PLUS_PLUS:
@@ -9514,6 +9561,7 @@
case META_LOOKBEHIND:
case META_LOOKBEHINDNOT:
+ case META_LOOKBEHIND_NA:
if (!set_lookbehind_lengths(&pptr, &max, &errorcode, &loopcount, NULL, cb))
return errorcode;
break;
Modified: code/trunk/src/pcre2_dfa_match.c
===================================================================
--- code/trunk/src/pcre2_dfa_match.c 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/src/pcre2_dfa_match.c 2019-07-13 11:12:03 UTC (rev 1130)
@@ -173,6 +173,8 @@
0, /* Assert not */
0, /* Assert behind */
0, /* Assert behind not */
+ 0, /* NA assert */
+ 0, /* NA assert behind */
0, /* ONCE */
0, /* SCRIPT_RUN */
0, 0, 0, 0, 0, /* BRA, BRAPOS, CBRA, CBRAPOS, COND */
@@ -248,6 +250,8 @@
0, /* Assert not */
0, /* Assert behind */
0, /* Assert behind not */
+ 0, /* NA assert */
+ 0, /* NA assert behind */
0, /* ONCE */
0, /* SCRIPT_RUN */
0, 0, 0, 0, 0, /* BRA, BRAPOS, CBRA, CBRAPOS, COND */
Modified: code/trunk/src/pcre2_error.c
===================================================================
--- code/trunk/src/pcre2_error.c 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/src/pcre2_error.c 2019-07-13 11:12:03 UTC (rev 1130)
@@ -185,6 +185,7 @@
"(*alpha_assertion) not recognized\0"
"script runs require Unicode support, which this version of PCRE2 does not have\0"
"too many capturing groups (maximum 65535)\0"
+ "atomic assertion expected after (?( or (?(?C)\0"
;
/* Match-time and UTF error texts are in the same format. */
Modified: code/trunk/src/pcre2_internal.h
===================================================================
--- code/trunk/src/pcre2_internal.h 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/src/pcre2_internal.h 2019-07-13 11:12:03 UTC (rev 1130)
@@ -883,6 +883,8 @@
#define STRING_atomic0 "atomic\0"
#define STRING_pla0 "pla\0"
#define STRING_plb0 "plb\0"
+#define STRING_napla0 "napla\0"
+#define STRING_naplb0 "naplb\0"
#define STRING_nla0 "nla\0"
#define STRING_nlb0 "nlb\0"
#define STRING_sr0 "sr\0"
@@ -889,6 +891,8 @@
#define STRING_asr0 "asr\0"
#define STRING_positive_lookahead0 "positive_lookahead\0"
#define STRING_positive_lookbehind0 "positive_lookbehind\0"
+#define STRING_non_atomic_positive_lookahead0 "non_atomic_positive_lookahead\0"
+#define STRING_non_atomic_positive_lookbehind0 "non_atomic_positive_lookbehind\0"
#define STRING_negative_lookahead0 "negative_lookahead\0"
#define STRING_negative_lookbehind0 "negative_lookbehind\0"
#define STRING_script_run0 "script_run\0"
@@ -1173,6 +1177,8 @@
#define STRING_atomic0 STR_a STR_t STR_o STR_m STR_i STR_c "\0"
#define STRING_pla0 STR_p STR_l STR_a "\0"
#define STRING_plb0 STR_p STR_l STR_b "\0"
+#define STRING_napla0 STR_n STR_a STR_p STR_l STR_a "\0"
+#define STRING_naplb0 STR_n STR_a STR_p STR_l STR_b "\0"
#define STRING_nla0 STR_n STR_l STR_a "\0"
#define STRING_nlb0 STR_n STR_l STR_b "\0"
#define STRING_sr0 STR_s STR_r "\0"
@@ -1179,6 +1185,8 @@
#define STRING_asr0 STR_a STR_s STR_r "\0"
#define STRING_positive_lookahead0 STR_p STR_o STR_s STR_i STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_a STR_h STR_e STR_a STR_d "\0"
#define STRING_positive_lookbehind0 STR_p STR_o STR_s STR_i STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_b STR_e STR_h STR_i STR_n STR_d "\0"
+#define STRING_non_atomic_positive_lookahead0 STR_n STR_o STR_n STR_UNDERSCORE STR_a STR_t STR_o STR_m STR_i STR_c STR_UNDERSCORE STR_p STR_o STR_s STR_i STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_a STR_h STR_e STR_a STR_d "\0"
+#define STRING_non_atomic_positive_lookbehind0 STR_n STR_o STR_n STR_UNDERSCORE STR_a STR_t STR_o STR_m STR_i STR_c STR_UNDERSCORE STR_p STR_o STR_s STR_i STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_b STR_e STR_h STR_i STR_n STR_d "\0"
#define STRING_negative_lookahead0 STR_n STR_e STR_g STR_a STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_a STR_h STR_e STR_a STR_d "\0"
#define STRING_negative_lookbehind0 STR_n STR_e STR_g STR_a STR_t STR_i STR_v STR_e STR_UNDERSCORE STR_l STR_o STR_o STR_k STR_b STR_e STR_h STR_i STR_n STR_d "\0"
#define STRING_script_run0 STR_s STR_c STR_r STR_i STR_p STR_t STR_UNDERSCORE STR_r STR_u STR_n "\0"
@@ -1303,7 +1311,7 @@
Starting from 1 (i.e. after OP_END), the values up to OP_EOD must correspond in
order to the list of escapes immediately above. Furthermore, values up to
OP_DOLLM must not be changed without adjusting the table called autoposstab in
-pcre2_auto_possess.c
+pcre2_auto_possess.c.
Whenever this list is updated, the two macro definitions that follow must be
updated to match. The possessification table called "opcode_possessify" in
@@ -1501,8 +1509,7 @@
OP_KETRMIN, /* 123 order. They are for groups the repeat for ever. */
OP_KETRPOS, /* 124 Possessive unlimited repeat. */
- /* The assertions must come before BRA, CBRA, ONCE, and COND, and the four
- asserts must remain in order. */
+ /* The assertions must come before BRA, CBRA, ONCE, and COND. */
OP_REVERSE, /* 125 Move pointer back - used in lookbehind assertions */
OP_ASSERT, /* 126 Positive lookahead */
@@ -1509,6 +1516,8 @@
OP_ASSERT_NOT, /* 127 Negative lookahead */
OP_ASSERTBACK, /* 128 Positive lookbehind */
OP_ASSERTBACK_NOT, /* 129 Negative lookbehind */
+ OP_ASSERT_NA, /* 130 Positive non-atomic lookahead */
+ OP_ASSERTBACK_NA, /* 131 Positive non-atomic lookbehind */
/* ONCE, SCRIPT_RUN, BRA, BRAPOS, CBRA, CBRAPOS, and COND must come
immediately after the assertions, with ONCE first, as there's a test for >=
@@ -1515,66 +1524,66 @@
ONCE for a subpattern that isn't an assertion. The POS versions must
immediately follow the non-POS versions in each case. */
- OP_ONCE, /* 130 Atomic group, contains captures */
- OP_SCRIPT_RUN, /* 131 Non-capture, but check characters' scripts */
- OP_BRA, /* 132 Start of non-capturing bracket */
- OP_BRAPOS, /* 133 Ditto, with unlimited, possessive repeat */
- OP_CBRA, /* 134 Start of capturing bracket */
- OP_CBRAPOS, /* 135 Ditto, with unlimited, possessive repeat */
- OP_COND, /* 136 Conditional group */
+ OP_ONCE, /* 132 Atomic group, contains captures */
+ OP_SCRIPT_RUN, /* 133 Non-capture, but check characters' scripts */
+ OP_BRA, /* 134 Start of non-capturing bracket */
+ OP_BRAPOS, /* 135 Ditto, with unlimited, possessive repeat */
+ OP_CBRA, /* 136 Start of capturing bracket */
+ OP_CBRAPOS, /* 137 Ditto, with unlimited, possessive repeat */
+ OP_COND, /* 138 Conditional group */
/* These five must follow the previous five, in the same order. There's a
check for >= SBRA to distinguish the two sets. */
- OP_SBRA, /* 137 Start of non-capturing bracket, check empty */
- OP_SBRAPOS, /* 138 Ditto, with unlimited, possessive repeat */
- OP_SCBRA, /* 139 Start of capturing bracket, check empty */
- OP_SCBRAPOS, /* 140 Ditto, with unlimited, possessive repeat */
- OP_SCOND, /* 141 Conditional group, check empty */
+ OP_SBRA, /* 139 Start of non-capturing bracket, check empty */
+ OP_SBRAPOS, /* 149 Ditto, with unlimited, possessive repeat */
+ OP_SCBRA, /* 141 Start of capturing bracket, check empty */
+ OP_SCBRAPOS, /* 142 Ditto, with unlimited, possessive repeat */
+ OP_SCOND, /* 143 Conditional group, check empty */
/* The next two pairs must (respectively) be kept together. */
- OP_CREF, /* 142 Used to hold a capture number as condition */
- OP_DNCREF, /* 143 Used to point to duplicate names as a condition */
- OP_RREF, /* 144 Used to hold a recursion number as condition */
- OP_DNRREF, /* 145 Used to point to duplicate names as a condition */
- OP_FALSE, /* 146 Always false (used by DEFINE and VERSION) */
- OP_TRUE, /* 147 Always true (used by VERSION) */
+ OP_CREF, /* 144 Used to hold a capture number as condition */
+ OP_DNCREF, /* 145 Used to point to duplicate names as a condition */
+ OP_RREF, /* 146 Used to hold a recursion number as condition */
+ OP_DNRREF, /* 147 Used to point to duplicate names as a condition */
+ OP_FALSE, /* 148 Always false (used by DEFINE and VERSION) */
+ OP_TRUE, /* 149 Always true (used by VERSION) */
- OP_BRAZERO, /* 148 These two must remain together and in this */
- OP_BRAMINZERO, /* 149 order. */
- OP_BRAPOSZERO, /* 150 */
+ OP_BRAZERO, /* 150 These two must remain together and in this */
+ OP_BRAMINZERO, /* 151 order. */
+ OP_BRAPOSZERO, /* 152 */
/* These are backtracking control verbs */
- OP_MARK, /* 151 always has an argument */
- OP_PRUNE, /* 152 */
- OP_PRUNE_ARG, /* 153 same, but with argument */
- OP_SKIP, /* 154 */
- OP_SKIP_ARG, /* 155 same, but with argument */
- OP_THEN, /* 156 */
- OP_THEN_ARG, /* 157 same, but with argument */
- OP_COMMIT, /* 158 */
- OP_COMMIT_ARG, /* 159 same, but with argument */
+ OP_MARK, /* 153 always has an argument */
+ OP_PRUNE, /* 154 */
+ OP_PRUNE_ARG, /* 155 same, but with argument */
+ OP_SKIP, /* 156 */
+ OP_SKIP_ARG, /* 157 same, but with argument */
+ OP_THEN, /* 158 */
+ OP_THEN_ARG, /* 159 same, but with argument */
+ OP_COMMIT, /* 160 */
+ OP_COMMIT_ARG, /* 161 same, but with argument */
/* These are forced failure and success verbs. FAIL and ACCEPT do accept an
argument, but these cases can be compiled as, for example, (*MARK:X)(*FAIL)
without the need for a special opcode. */
- OP_FAIL, /* 160 */
- OP_ACCEPT, /* 161 */
- OP_ASSERT_ACCEPT, /* 162 Used inside assertions */
- OP_CLOSE, /* 163 Used before OP_ACCEPT to close open captures */
+ OP_FAIL, /* 162 */
+ OP_ACCEPT, /* 163 */
+ OP_ASSERT_ACCEPT, /* 164 Used inside assertions */
+ OP_CLOSE, /* 165 Used before OP_ACCEPT to close open captures */
/* This is used to skip a subpattern with a {0} quantifier */
- OP_SKIPZERO, /* 164 */
+ OP_SKIPZERO, /* 166 */
/* This is used to identify a DEFINE group during compilation so that it can
be checked for having only one branch. It is changed to OP_FALSE before
compilation finishes. */
- OP_DEFINE, /* 165 */
+ OP_DEFINE, /* 167 */
/* This is not an opcode, but is used to check that tables indexed by opcode
are the correct length, in order to catch updating errors - there have been
@@ -1587,7 +1596,7 @@
/* *** NOTE NOTE NOTE *** Whenever the list above is updated, the two macro
definitions that follow must also be updated to match. There are also tables
called "opcode_possessify" in pcre2_compile.c and "coptable" and "poptable" in
-pcre2_dfa_exec.c that must be updated. */
+pcre2_dfa_match.c that must be updated. */
/* This macro defines textual names for all the opcodes. These are used only
@@ -1620,7 +1629,9 @@
"class", "nclass", "xclass", "Ref", "Refi", "DnRef", "DnRefi", \
"Recurse", "Callout", "CalloutStr", \
"Alt", "Ket", "KetRmax", "KetRmin", "KetRpos", \
- "Reverse", "Assert", "Assert not", "AssertB", "AssertB not", \
+ "Reverse", "Assert", "Assert not", \
+ "Assert back", "Assert back not", \
+ "Non-atomic assert", "Non-atomic assert back", \
"Once", \
"Script run", \
"Bra", "BraPos", "CBra", "CBraPos", \
@@ -1705,6 +1716,8 @@
1+LINK_SIZE, /* Assert not */ \
1+LINK_SIZE, /* Assert behind */ \
1+LINK_SIZE, /* Assert behind not */ \
+ 1+LINK_SIZE, /* NA Assert */ \
+ 1+LINK_SIZE, /* NA Assert behind */ \
1+LINK_SIZE, /* ONCE */ \
1+LINK_SIZE, /* SCRIPT_RUN */ \
1+LINK_SIZE, /* BRA */ \
Modified: code/trunk/src/pcre2_match.c
===================================================================
--- code/trunk/src/pcre2_match.c 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/src/pcre2_match.c 2019-07-13 11:12:03 UTC (rev 1130)
@@ -5127,6 +5127,8 @@
case OP_ASSERT:
case OP_ASSERTBACK:
+ case OP_ASSERT_NA:
+ case OP_ASSERTBACK_NA:
Lframe_type = GF_NOCAPTURE | Fop;
for (;;)
{
@@ -5497,10 +5499,20 @@
case OP_SCOND:
break;
- /* Positive assertions are like OP_ONCE, except that in addition the
+ /* Non-atomic positive assertions are like OP_BRA, except that the
subject pointer must be put back to where it was at the start of the
assertion. */
+ case OP_ASSERT_NA:
+ case OP_ASSERTBACK_NA:
+ if (Feptr > mb->last_used_ptr) mb->last_used_ptr = Feptr;
+ Feptr = P->eptr;
+ break;
+
+ /* Atomic positive assertions are like OP_ONCE, except that in addition
+ the subject pointer must be put back to where it was at the start of the
+ assertion. */
+
case OP_ASSERT:
case OP_ASSERTBACK:
if (Feptr > mb->last_used_ptr) mb->last_used_ptr = Feptr;
Modified: code/trunk/src/pcre2_printint.c
===================================================================
--- code/trunk/src/pcre2_printint.c 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/src/pcre2_printint.c 2019-07-13 11:12:03 UTC (rev 1130)
@@ -392,6 +392,8 @@
case OP_ASSERT_NOT:
case OP_ASSERTBACK:
case OP_ASSERTBACK_NOT:
+ case OP_ASSERT_NA:
+ case OP_ASSERTBACK_NA:
case OP_ONCE:
case OP_SCRIPT_RUN:
case OP_COND:
Modified: code/trunk/src/pcre2_study.c
===================================================================
--- code/trunk/src/pcre2_study.c 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/src/pcre2_study.c 2019-07-13 11:12:03 UTC (rev 1130)
@@ -240,6 +240,8 @@
case OP_ASSERT_NOT:
case OP_ASSERTBACK:
case OP_ASSERTBACK_NOT:
+ case OP_ASSERT_NA:
+ case OP_ASSERTBACK_NA:
do cc += GET(cc, 1); while (*cc == OP_ALT);
/* Fall through */
@@ -1089,6 +1091,7 @@
case OP_ONCE:
case OP_SCRIPT_RUN:
case OP_ASSERT:
+ case OP_ASSERT_NA:
rc = set_start_bits(re, tcode, utf);
if (rc == SSB_FAIL || rc == SSB_UNKNOWN) return rc;
if (rc == SSB_DONE) try_next = FALSE; else
@@ -1131,6 +1134,7 @@
case OP_ASSERT_NOT:
case OP_ASSERTBACK:
case OP_ASSERTBACK_NOT:
+ case OP_ASSERTBACK_NA:
do tcode += GET(tcode, 1); while (*tcode == OP_ALT);
tcode += 1 + LINK_SIZE;
break;
Modified: code/trunk/testdata/testinput2
===================================================================
--- code/trunk/testdata/testinput2 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/testdata/testinput2 2019-07-13 11:12:03 UTC (rev 1130)
@@ -5653,4 +5653,33 @@
# Multiplication overflow
/(X{65535})(?<=\1{32770})/
+# ---- Non-atomic assertion tests ----
+
+# Expect error: not allowed as a condition
+/(?(*napla:xx)bc)/
+
+/\A(*pla:.*\b(\w++))(?>.*?\b\1\b){3}/
+ word1 word3 word1 word2 word3 word2 word2 word1 word3 word4
+
+/\A(*napla:.*\b(\w++))(?>.*?\b\1\b){3}/
+ word1 word3 word1 word2 word3 word2 word2 word1 word3 word4
+
+/(*plb:(.)..|(.)...)(\1|\2)/
+ abcdb\=offset=4
+ abcda\=offset=4
+
+/(*naplb:(.)..|(.)...)(\1|\2)/
+ abcdb\=offset=4
+ abcda\=offset=4
+
+/(*non_atomic_positive_lookahead:ab)/B
+
+/(*non_atomic_positive_lookbehind:ab)/B
+
+/(*pla:ab+)/B
+
+/(*napla:ab+)/B
+
+# ----
+
# End of testinput2
Modified: code/trunk/testdata/testoutput2
===================================================================
--- code/trunk/testdata/testoutput2 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/testdata/testoutput2 2019-07-13 11:12:03 UTC (rev 1130)
@@ -11117,7 +11117,7 @@
------------------------------------------------------------------
Bra
Brazero
- AssertB
+ Assert back
Reverse
CBra 1
abc
@@ -13346,7 +13346,7 @@
Ket
red
\b
- AssertB
+ Assert back
Reverse
\w
Ket
@@ -13403,7 +13403,7 @@
Once
\s*+
Ket
- AssertB
+ Assert back
Reverse
\w
Ket
@@ -16619,7 +16619,7 @@
/(?<=(?=.){4,5}x)/B
------------------------------------------------------------------
Bra
- AssertB
+ Assert back
Reverse
Assert
Any
@@ -17086,6 +17086,87 @@
/(X{65535})(?<=\1{32770})/
Failed: error 187 at offset 10: lookbehind assertion is too long
+# ---- Non-atomic assertion tests ----
+
+# Expect error: not allowed as a condition
+/(?(*napla:xx)bc)/
+Failed: error 198 at offset 9: atomic assertion expected after (?( or (?(?C)
+
+/\A(*pla:.*\b(\w++))(?>.*?\b\1\b){3}/
+ word1 word3 word1 word2 word3 word2 word2 word1 word3 word4
+No match
+
+/\A(*napla:.*\b(\w++))(?>.*?\b\1\b){3}/
+ word1 word3 word1 word2 word3 word2 word2 word1 word3 word4
+ 0: word1 word3 word1 word2 word3 word2 word2 word1 word3
+ 1: word3
+
+/(*plb:(.)..|(.)...)(\1|\2)/
+ abcdb\=offset=4
+ 0: b
+ 1: b
+ 2: <unset>
+ 3: b
+ abcda\=offset=4
+No match
+
+/(*naplb:(.)..|(.)...)(\1|\2)/
+ abcdb\=offset=4
+ 0: b
+ 1: b
+ 2: <unset>
+ 3: b
+ abcda\=offset=4
+ 0: a
+ 1: <unset>
+ 2: a
+ 3: a
+
+/(*non_atomic_positive_lookahead:ab)/B
+------------------------------------------------------------------
+ Bra
+ Non-atomic assert
+ ab
+ Ket
+ Ket
+ End
+------------------------------------------------------------------
+
+/(*non_atomic_positive_lookbehind:ab)/B
+------------------------------------------------------------------
+ Bra
+ Non-atomic assert back
+ Reverse
+ ab
+ Ket
+ Ket
+ End
+------------------------------------------------------------------
+
+/(*pla:ab+)/B
+------------------------------------------------------------------
+ Bra
+ Assert
+ a
+ b++
+ Ket
+ Ket
+ End
+------------------------------------------------------------------
+
+/(*napla:ab+)/B
+------------------------------------------------------------------
+ Bra
+ Non-atomic assert
+ a
+ b+
+ Ket
+ Ket
+ End
+------------------------------------------------------------------
+
+# ----
+
# End of testinput2
Error -70: PCRE2_ERROR_BADDATA (unknown error number)
Error -62: bad serialized data
Modified: code/trunk/testdata/testoutput5
===================================================================
--- code/trunk/testdata/testoutput5 2019-07-10 14:57:43 UTC (rev 1129)
+++ code/trunk/testdata/testoutput5 2019-07-13 11:12:03 UTC (rev 1130)
@@ -4019,7 +4019,7 @@
------------------------------------------------------------------
Bra
\b
- AssertB
+ Assert back
Reverse
prop Xwd
Ket
@@ -4198,7 +4198,7 @@
------------------------------------------------------------------
Bra
^
- AssertB not
+ Assert back not
Assert
\x{10385c}
Ket
@@ -4831,7 +4831,7 @@
/(?<!)(*sr:)/B
------------------------------------------------------------------
Bra
- AssertB not
+ Assert back not
Ket
Script run
Ket
@@ -4842,7 +4842,7 @@
/(?<=abc(?=X(*sr:BXY)CCC)XBXYCCC)./B
------------------------------------------------------------------
Bra
- AssertB
+ Assert back
Reverse
abc
Assert
