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1  ChangeLog for PCRE  ChangeLog for PCRE
2  ------------------  ------------------
3    
4  Version 8.01 11-Dec-09  Version 8.31
5  ----------------------  -----------------------------
6    
7  1.  If a pattern contained a conditional subpattern with only one branch (in  1.  Fixing a wrong JIT test case and some compiler warnings.
8      particular, this includes all (DEFINE) patterns), a call to pcre_study()  
9      computed the wrong minimum data length (which is of course zero for such  2.  Removed a bashism from the RunTest script.
10      subpatterns).  
11    3.  Add a cast to pcre_exec.c to fix the warning "unary minus operator applied
12        to unsigned type, result still unsigned" that was given by an MS compiler
13        on encountering the code "-sizeof(xxx)".
14    
15    4.  Partial matching support is added to the JIT compiler.
16    
17    5.  Fixed several bugs concerned with partial matching of items that consist
18        of more than one character:
19    
20  2.  For patterns such as (?i)a(?-i)b|c where an option setting at the start of      (a) /^(..)\1/ did not partially match "aba" because checking references was
21            done on an "all or nothing" basis. This also applied to repeated
22            references.
23    
24        (b) \R did not give a hard partial match if \r was found at the end of the
25            subject.
26    
27        (c) \X did not give a hard partial match after matching one or more
28            characters at the end of the subject.
29    
30        (d) When newline was set to CRLF, a pattern such as /a$/ did not recognize
31            a partial match for the string "\r".
32    
33        (e) When newline was set to CRLF, the metacharacter "." did not recognize
34            a partial match for a CR character at the end of the subject string.
35    
36    6.  When matching is performed using JIT-compiled code, the flag bit
37        PCRE_EXTRA_USED_JIT is set in the pcre_extra block and can be tested by the
38        caller. This bit is checked by pcretest if JIT is requested by /S++ or -s++
39        (instead of just /S+ or -s+) and the text "(JIT)" added to the output if
40        the bit is set.
41    
42    
43    Version 8.30 04-February-2012
44    -----------------------------
45    
46    1.  Renamed "isnumber" as "is_a_number" because in some Mac environments this
47        name is defined in ctype.h.
48    
49    2.  Fixed a bug in fixed-length calculation for lookbehinds that would show up
50        only in quite long subpatterns.
51    
52    3.  Removed the function pcre_info(), which has been obsolete and deprecated
53        since it was replaced by pcre_fullinfo() in February 2000.
54    
55    4.  For a non-anchored pattern, if (*SKIP) was given with a name that did not
56        match a (*MARK), and the match failed at the start of the subject, a
57        reference to memory before the start of the subject could occur. This bug
58        was introduced by fix 17 of release 8.21.
59    
60    5.  A reference to an unset group with zero minimum repetition was giving
61        totally wrong answers (in non-JavaScript-compatibility mode). For example,
62        /(another)?(\1?)test/ matched against "hello world test". This bug was
63        introduced in release 8.13.
64    
65    6.  Add support for 16-bit character strings (a large amount of work involving
66        many changes and refactorings).
67    
68    7.  RunGrepTest failed on msys because \r\n was replaced by whitespace when the
69        command "pattern=`printf 'xxx\r\njkl'`" was run. The pattern is now taken
70        from a file.
71    
72    8.  Ovector size of 2 is also supported by JIT based pcre_exec (the ovector size
73        rounding is not applied in this particular case).
74    
75    9.  The invalid Unicode surrogate codepoints U+D800 to U+DFFF are now rejected
76        if they appear, or are escaped, in patterns.
77    
78    10. Get rid of a number of -Wunused-but-set-variable warnings.
79    
80    11. The pattern /(?=(*:x))(q|)/ matches an empty string, and returns the mark
81        "x". The similar pattern /(?=(*:x))((*:y)q|)/ did not return a mark at all.
82        Oddly, Perl behaves the same way. PCRE has been fixed so that this pattern
83        also returns the mark "x". This bug applied to capturing parentheses,
84        non-capturing parentheses, and atomic parentheses. It also applied to some
85        assertions.
86    
87    12. Stephen Kelly's patch to CMakeLists.txt allows it to parse the version
88        information out of configure.ac instead of relying on pcre.h.generic, which
89        is not stored in the repository.
90    
91    13. Applied Dmitry V. Levin's patch for a more portable method for linking with
92        -lreadline.
93    
94    14. ZH added PCRE_CONFIG_JITTARGET; added its output to pcretest -C.
95    
96    15. Applied Graycode's patch to put the top-level frame on the stack rather
97        than the heap when not using the stack for recursion. This gives a
98        performance improvement in many cases when recursion is not deep.
99    
100    16. Experimental code added to "pcretest -C" to output the stack frame size.
101    
102    
103    Version 8.21 12-Dec-2011
104    ------------------------
105    
106    1.  Updating the JIT compiler.
107    
108    2.  JIT compiler now supports OP_NCREF, OP_RREF and OP_NRREF. New test cases
109        are added as well.
110    
111    3.  Fix cache-flush issue on PowerPC (It is still an experimental JIT port).
112        PCRE_EXTRA_TABLES is not suported by JIT, and should be checked before
113        calling _pcre_jit_exec. Some extra comments are added.
114    
115    4.  (*MARK) settings inside atomic groups that do not contain any capturing
116        parentheses, for example, (?>a(*:m)), were not being passed out. This bug
117        was introduced by change 18 for 8.20.
118    
119    5.  Supporting of \x, \U and \u in JavaScript compatibility mode based on the
120        ECMA-262 standard.
121    
122    6.  Lookbehinds such as (?<=a{2}b) that contained a fixed repetition were
123        erroneously being rejected as "not fixed length" if PCRE_CASELESS was set.
124        This bug was probably introduced by change 9 of 8.13.
125    
126    7.  While fixing 6 above, I noticed that a number of other items were being
127        incorrectly rejected as "not fixed length". This arose partly because newer
128        opcodes had not been added to the fixed-length checking code. I have (a)
129        corrected the bug and added tests for these items, and (b) arranged for an
130        error to occur if an unknown opcode is encountered while checking for fixed
131        length instead of just assuming "not fixed length". The items that were
132        rejected were: (*ACCEPT), (*COMMIT), (*FAIL), (*MARK), (*PRUNE), (*SKIP),
133        (*THEN), \h, \H, \v, \V, and single character negative classes with fixed
134        repetitions, e.g. [^a]{3}, with and without PCRE_CASELESS.
135    
136    8.  A possessively repeated conditional subpattern such as (?(?=c)c|d)++ was
137        being incorrectly compiled and would have given unpredicatble results.
138    
139    9.  A possessively repeated subpattern with minimum repeat count greater than
140        one behaved incorrectly. For example, (A){2,}+ behaved as if it was
141        (A)(A)++ which meant that, after a subsequent mismatch, backtracking into
142        the first (A) could occur when it should not.
143    
144    10. Add a cast and remove a redundant test from the code.
145    
146    11. JIT should use pcre_malloc/pcre_free for allocation.
147    
148    12. Updated pcre-config so that it no longer shows -L/usr/lib, which seems
149        best practice nowadays, and helps with cross-compiling. (If the exec_prefix
150        is anything other than /usr, -L is still shown).
151    
152    13. In non-UTF-8 mode, \C is now supported in lookbehinds and DFA matching.
153    
154    14. Perl does not support \N without a following name in a [] class; PCRE now
155        also gives an error.
156    
157    15. If a forward reference was repeated with an upper limit of around 2000,
158        it caused the error "internal error: overran compiling workspace". The
159        maximum number of forward references (including repeats) was limited by the
160        internal workspace, and dependent on the LINK_SIZE. The code has been
161        rewritten so that the workspace expands (via pcre_malloc) if necessary, and
162        the default depends on LINK_SIZE. There is a new upper limit (for safety)
163        of around 200,000 forward references. While doing this, I also speeded up
164        the filling in of repeated forward references.
165    
166    16. A repeated forward reference in a pattern such as (a)(?2){2}(.) was
167        incorrectly expecting the subject to contain another "a" after the start.
168    
169    17. When (*SKIP:name) is activated without a corresponding (*MARK:name) earlier
170        in the match, the SKIP should be ignored. This was not happening; instead
171        the SKIP was being treated as NOMATCH. For patterns such as
172        /A(*MARK:A)A+(*SKIP:B)Z|AAC/ this meant that the AAC branch was never
173        tested.
174    
175    18. The behaviour of (*MARK), (*PRUNE), and (*THEN) has been reworked and is
176        now much more compatible with Perl, in particular in cases where the result
177        is a non-match for a non-anchored pattern. For example, if
178        /b(*:m)f|a(*:n)w/ is matched against "abc", the non-match returns the name
179        "m", where previously it did not return a name. A side effect of this
180        change is that for partial matches, the last encountered mark name is
181        returned, as for non matches. A number of tests that were previously not
182        Perl-compatible have been moved into the Perl-compatible test files. The
183        refactoring has had the pleasing side effect of removing one argument from
184        the match() function, thus reducing its stack requirements.
185    
186    19. If the /S+ option was used in pcretest to study a pattern using JIT,
187        subsequent uses of /S (without +) incorrectly behaved like /S+.
188    
189    21. Retrieve executable code size support for the JIT compiler and fixing
190        some warnings.
191    
192    22. A caseless match of a UTF-8 character whose other case uses fewer bytes did
193        not work when the shorter character appeared right at the end of the
194        subject string.
195    
196    23. Added some (int) casts to non-JIT modules to reduce warnings on 64-bit
197        systems.
198    
199    24. Added PCRE_INFO_JITSIZE to pass on the value from (21) above, and also
200        output it when the /M option is used in pcretest.
201    
202    25. The CheckMan script was not being included in the distribution. Also, added
203        an explicit "perl" to run Perl scripts from the PrepareRelease script
204        because this is reportedly needed in Windows.
205    
206    26. If study data was being save in a file and studying had not found a set of
207        "starts with" bytes for the pattern, the data written to the file (though
208        never used) was taken from uninitialized memory and so caused valgrind to
209        complain.
210    
211    27. Updated RunTest.bat as provided by Sheri Pierce.
212    
213    28. Fixed a possible uninitialized memory bug in pcre_jit_compile.c.
214    
215    29. Computation of memory usage for the table of capturing group names was
216        giving an unnecessarily large value.
217    
218    
219    Version 8.20 21-Oct-2011
220    ------------------------
221    
222    1.  Change 37 of 8.13 broke patterns like [:a]...[b:] because it thought it had
223        a POSIX class. After further experiments with Perl, which convinced me that
224        Perl has bugs and confusions, a closing square bracket is no longer allowed
225        in a POSIX name. This bug also affected patterns with classes that started
226        with full stops.
227    
228    2.  If a pattern such as /(a)b|ac/ is matched against "ac", there is no
229        captured substring, but while checking the failing first alternative,
230        substring 1 is temporarily captured. If the output vector supplied to
231        pcre_exec() was not big enough for this capture, the yield of the function
232        was still zero ("insufficient space for captured substrings"). This cannot
233        be totally fixed without adding another stack variable, which seems a lot
234        of expense for a edge case. However, I have improved the situation in cases
235        such as /(a)(b)x|abc/ matched against "abc", where the return code
236        indicates that fewer than the maximum number of slots in the ovector have
237        been set.
238    
239    3.  Related to (2) above: when there are more back references in a pattern than
240        slots in the output vector, pcre_exec() uses temporary memory during
241        matching, and copies in the captures as far as possible afterwards. It was
242        using the entire output vector, but this conflicts with the specification
243        that only 2/3 is used for passing back captured substrings. Now it uses
244        only the first 2/3, for compatibility. This is, of course, another edge
245        case.
246    
247    4.  Zoltan Herczeg's just-in-time compiler support has been integrated into the
248        main code base, and can be used by building with --enable-jit. When this is
249        done, pcregrep automatically uses it unless --disable-pcregrep-jit or the
250        runtime --no-jit option is given.
251    
252    5.  When the number of matches in a pcre_dfa_exec() run exactly filled the
253        ovector, the return from the function was zero, implying that there were
254        other matches that did not fit. The correct "exactly full" value is now
255        returned.
256    
257    6.  If a subpattern that was called recursively or as a subroutine contained
258        (*PRUNE) or any other control that caused it to give a non-standard return,
259        invalid errors such as "Error -26 (nested recursion at the same subject
260        position)" or even infinite loops could occur.
261    
262    7.  If a pattern such as /a(*SKIP)c|b(*ACCEPT)|/ was studied, it stopped
263        computing the minimum length on reaching *ACCEPT, and so ended up with the
264        wrong value of 1 rather than 0. Further investigation indicates that
265        computing a minimum subject length in the presence of *ACCEPT is difficult
266        (think back references, subroutine calls), and so I have changed the code
267        so that no minimum is registered for a pattern that contains *ACCEPT.
268    
269    8.  If (*THEN) was present in the first (true) branch of a conditional group,
270        it was not handled as intended. [But see 16 below.]
271    
272    9.  Replaced RunTest.bat and CMakeLists.txt with improved versions provided by
273        Sheri Pierce.
274    
275    10. A pathological pattern such as /(*ACCEPT)a/ was miscompiled, thinking that
276        the first byte in a match must be "a".
277    
278    11. Change 17 for 8.13 increased the recursion depth for patterns like
279        /a(?:.)*?a/ drastically. I've improved things by remembering whether a
280        pattern contains any instances of (*THEN). If it does not, the old
281        optimizations are restored. It would be nice to do this on a per-group
282        basis, but at the moment that is not feasible.
283    
284    12. In some environments, the output of pcretest -C is CRLF terminated. This
285        broke RunTest's code that checks for the link size. A single white space
286        character after the value is now allowed for.
287    
288    13. RunTest now checks for the "fr" locale as well as for "fr_FR" and "french".
289        For "fr", it uses the Windows-specific input and output files.
290    
291    14. If (*THEN) appeared in a group that was called recursively or as a
292        subroutine, it did not work as intended. [But see next item.]
293    
294    15. Consider the pattern /A (B(*THEN)C) | D/ where A, B, C, and D are complex
295        pattern fragments (but not containing any | characters). If A and B are
296        matched, but there is a failure in C so that it backtracks to (*THEN), PCRE
297        was behaving differently to Perl. PCRE backtracked into A, but Perl goes to
298        D. In other words, Perl considers parentheses that do not contain any |
299        characters to be part of a surrounding alternative, whereas PCRE was
300        treading (B(*THEN)C) the same as (B(*THEN)C|(*FAIL)) -- which Perl handles
301        differently. PCRE now behaves in the same way as Perl, except in the case
302        of subroutine/recursion calls such as (?1) which have in any case always
303        been different (but PCRE had them first :-).
304    
305    16. Related to 15 above: Perl does not treat the | in a conditional group as
306        creating alternatives. Such a group is treated in the same way as an
307        ordinary group without any | characters when processing (*THEN). PCRE has
308        been changed to match Perl's behaviour.
309    
310    17. If a user had set PCREGREP_COLO(U)R to something other than 1:31, the
311        RunGrepTest script failed.
312    
313    18. Change 22 for version 13 caused atomic groups to use more stack. This is
314        inevitable for groups that contain captures, but it can lead to a lot of
315        stack use in large patterns. The old behaviour has been restored for atomic
316        groups that do not contain any capturing parentheses.
317    
318    19. If the PCRE_NO_START_OPTIMIZE option was set for pcre_compile(), it did not
319        suppress the check for a minimum subject length at run time. (If it was
320        given to pcre_exec() or pcre_dfa_exec() it did work.)
321    
322    20. Fixed an ASCII-dependent infelicity in pcretest that would have made it
323        fail to work when decoding hex characters in data strings in EBCDIC
324        environments.
325    
326    21. It appears that in at least one Mac OS environment, the isxdigit() function
327        is implemented as a macro that evaluates to its argument more than once,
328        contravening the C 90 Standard (I haven't checked a later standard). There
329        was an instance in pcretest which caused it to go wrong when processing
330        \x{...} escapes in subject strings. The has been rewritten to avoid using
331        things like p++ in the argument of isxdigit().
332    
333    
334    Version 8.13 16-Aug-2011
335    ------------------------
336    
337    1.  The Unicode data tables have been updated to Unicode 6.0.0.
338    
339    2.  Two minor typos in pcre_internal.h have been fixed.
340    
341    3.  Added #include <string.h> to pcre_scanner_unittest.cc, pcrecpp.cc, and
342        pcrecpp_unittest.cc. They are needed for strcmp(), memset(), and strchr()
343        in some environments (e.g. Solaris 10/SPARC using Sun Studio 12U2).
344    
345    4.  There were a number of related bugs in the code for matching backrefences
346        caselessly in UTF-8 mode when codes for the characters concerned were
347        different numbers of bytes. For example, U+023A and U+2C65 are an upper
348        and lower case pair, using 2 and 3 bytes, respectively. The main bugs were:
349        (a) A reference to 3 copies of a 2-byte code matched only 2 of a 3-byte
350        code. (b) A reference to 2 copies of a 3-byte code would not match 2 of a
351        2-byte code at the end of the subject (it thought there wasn't enough data
352        left).
353    
354    5.  Comprehensive information about what went wrong is now returned by
355        pcre_exec() and pcre_dfa_exec() when the UTF-8 string check fails, as long
356        as the output vector has at least 2 elements. The offset of the start of
357        the failing character and a reason code are placed in the vector.
358    
359    6.  When the UTF-8 string check fails for pcre_compile(), the offset that is
360        now returned is for the first byte of the failing character, instead of the
361        last byte inspected. This is an incompatible change, but I hope it is small
362        enough not to be a problem. It makes the returned offset consistent with
363        pcre_exec() and pcre_dfa_exec().
364    
365    7.  pcretest now gives a text phrase as well as the error number when
366        pcre_exec() or pcre_dfa_exec() fails; if the error is a UTF-8 check
367        failure, the offset and reason code are output.
368    
369    8.  When \R was used with a maximizing quantifier it failed to skip backwards
370        over a \r\n pair if the subsequent match failed. Instead, it just skipped
371        back over a single character (\n). This seems wrong (because it treated the
372        two characters as a single entity when going forwards), conflicts with the
373        documentation that \R is equivalent to (?>\r\n|\n|...etc), and makes the
374        behaviour of \R* different to (\R)*, which also seems wrong. The behaviour
375        has been changed.
376    
377    9.  Some internal refactoring has changed the processing so that the handling
378        of the PCRE_CASELESS and PCRE_MULTILINE options is done entirely at compile
379        time (the PCRE_DOTALL option was changed this way some time ago: version
380        7.7 change 16). This has made it possible to abolish the OP_OPT op code,
381        which was always a bit of a fudge. It also means that there is one less
382        argument for the match() function, which reduces its stack requirements
383        slightly. This change also fixes an incompatibility with Perl: the pattern
384        (?i:([^b]))(?1) should not match "ab", but previously PCRE gave a match.
385    
386    10. More internal refactoring has drastically reduced the number of recursive
387        calls to match() for possessively repeated groups such as (abc)++ when
388        using pcre_exec().
389    
390    11. While implementing 10, a number of bugs in the handling of groups were
391        discovered and fixed:
392    
393        (?<=(a)+) was not diagnosed as invalid (non-fixed-length lookbehind).
394        (a|)*(?1) gave a compile-time internal error.
395        ((a|)+)+  did not notice that the outer group could match an empty string.
396        (^a|^)+   was not marked as anchored.
397        (.*a|.*)+ was not marked as matching at start or after a newline.
398    
399    12. Yet more internal refactoring has removed another argument from the match()
400        function. Special calls to this function are now indicated by setting a
401        value in a variable in the "match data" data block.
402    
403    13. Be more explicit in pcre_study() instead of relying on "default" for
404        opcodes that mean there is no starting character; this means that when new
405        ones are added and accidentally left out of pcre_study(), testing should
406        pick them up.
407    
408    14. The -s option of pcretest has been documented for ages as being an old
409        synonym of -m (show memory usage). I have changed it to mean "force study
410        for every regex", that is, assume /S for every regex. This is similar to -i
411        and -d etc. It's slightly incompatible, but I'm hoping nobody is still
412        using it. It makes it easier to run collections of tests with and without
413        study enabled, and thereby test pcre_study() more easily. All the standard
414        tests are now run with and without -s (but some patterns can be marked as
415        "never study" - see 20 below).
416    
417    15. When (*ACCEPT) was used in a subpattern that was called recursively, the
418        restoration of the capturing data to the outer values was not happening
419        correctly.
420    
421    16. If a recursively called subpattern ended with (*ACCEPT) and matched an
422        empty string, and PCRE_NOTEMPTY was set, pcre_exec() thought the whole
423        pattern had matched an empty string, and so incorrectly returned a no
424        match.
425    
426    17. There was optimizing code for the last branch of non-capturing parentheses,
427        and also for the obeyed branch of a conditional subexpression, which used
428        tail recursion to cut down on stack usage. Unfortunately, now that there is
429        the possibility of (*THEN) occurring in these branches, tail recursion is
430        no longer possible because the return has to be checked for (*THEN). These
431        two optimizations have therefore been removed. [But see 8.20/11 above.]
432    
433    18. If a pattern containing \R was studied, it was assumed that \R always
434        matched two bytes, thus causing the minimum subject length to be
435        incorrectly computed because \R can also match just one byte.
436    
437    19. If a pattern containing (*ACCEPT) was studied, the minimum subject length
438        was incorrectly computed.
439    
440    20. If /S is present twice on a test pattern in pcretest input, it now
441        *disables* studying, thereby overriding the use of -s on the command line
442        (see 14 above). This is necessary for one or two tests to keep the output
443        identical in both cases.
444    
445    21. When (*ACCEPT) was used in an assertion that matched an empty string and
446        PCRE_NOTEMPTY was set, PCRE applied the non-empty test to the assertion.
447    
448    22. When an atomic group that contained a capturing parenthesis was
449        successfully matched, but the branch in which it appeared failed, the
450        capturing was not being forgotten if a higher numbered group was later
451        captured. For example, /(?>(a))b|(a)c/ when matching "ac" set capturing
452        group 1 to "a", when in fact it should be unset. This applied to multi-
453        branched capturing and non-capturing groups, repeated or not, and also to
454        positive assertions (capturing in negative assertions does not happen
455        in PCRE) and also to nested atomic groups.
456    
457    23. Add the ++ qualifier feature to pcretest, to show the remainder of the
458        subject after a captured substring, to make it easier to tell which of a
459        number of identical substrings has been captured.
460    
461    24. The way atomic groups are processed by pcre_exec() has been changed so that
462        if they are repeated, backtracking one repetition now resets captured
463        values correctly. For example, if ((?>(a+)b)+aabab) is matched against
464        "aaaabaaabaabab" the value of captured group 2 is now correctly recorded as
465        "aaa". Previously, it would have been "a". As part of this code
466        refactoring, the way recursive calls are handled has also been changed.
467    
468    25. If an assertion condition captured any substrings, they were not passed
469        back unless some other capturing happened later. For example, if
470        (?(?=(a))a) was matched against "a", no capturing was returned.
471    
472    26. When studying a pattern that contained subroutine calls or assertions,
473        the code for finding the minimum length of a possible match was handling
474        direct recursions such as (xxx(?1)|yyy) but not mutual recursions (where
475        group 1 called group 2 while simultaneously a separate group 2 called group
476        1). A stack overflow occurred in this case. I have fixed this by limiting
477        the recursion depth to 10.
478    
479    27. Updated RunTest.bat in the distribution to the version supplied by Tom
480        Fortmann. This supports explicit test numbers on the command line, and has
481        argument validation and error reporting.
482    
483    28. An instance of \X with an unlimited repeat could fail if at any point the
484        first character it looked at was a mark character.
485    
486    29. Some minor code refactoring concerning Unicode properties and scripts
487        should reduce the stack requirement of match() slightly.
488    
489    30. Added the '=' option to pcretest to check the setting of unused capturing
490        slots at the end of the pattern, which are documented as being -1, but are
491        not included in the return count.
492    
493    31. If \k was not followed by a braced, angle-bracketed, or quoted name, PCRE
494        compiled something random. Now it gives a compile-time error (as does
495        Perl).
496    
497    32. A *MARK encountered during the processing of a positive assertion is now
498        recorded and passed back (compatible with Perl).
499    
500    33. If --only-matching or --colour was set on a pcregrep call whose pattern
501        had alternative anchored branches, the search for a second match in a line
502        was done as if at the line start. Thus, for example, /^01|^02/ incorrectly
503        matched the line "0102" twice. The same bug affected patterns that started
504        with a backwards assertion. For example /\b01|\b02/ also matched "0102"
505        twice.
506    
507    34. Previously, PCRE did not allow quantification of assertions. However, Perl
508        does, and because of capturing effects, quantifying parenthesized
509        assertions may at times be useful. Quantifiers are now allowed for
510        parenthesized assertions.
511    
512    35. A minor code tidy in pcre_compile() when checking options for \R usage.
513    
514    36. \g was being checked for fancy things in a character class, when it should
515        just be a literal "g".
516    
517    37. PCRE was rejecting [:a[:digit:]] whereas Perl was not. It seems that the
518        appearance of a nested POSIX class supersedes an apparent external class.
519        For example, [:a[:digit:]b:] matches "a", "b", ":", or a digit. Also,
520        unescaped square brackets may also appear as part of class names. For
521        example, [:a[:abc]b:] gives unknown class "[:abc]b:]". PCRE now behaves
522        more like Perl. (But see 8.20/1 above.)
523    
524    38. PCRE was giving an error for \N with a braced quantifier such as {1,} (this
525        was because it thought it was \N{name}, which is not supported).
526    
527    39. Add minix to OS list not supporting the -S option in pcretest.
528    
529    40. PCRE tries to detect cases of infinite recursion at compile time, but it
530        cannot analyze patterns in sufficient detail to catch mutual recursions
531        such as ((?1))((?2)). There is now a runtime test that gives an error if a
532        subgroup is called recursively as a subpattern for a second time at the
533        same position in the subject string. In previous releases this might have
534        been caught by the recursion limit, or it might have run out of stack.
535    
536    41. A pattern such as /(?(R)a+|(?R)b)/ is quite safe, as the recursion can
537        happen only once. PCRE was, however incorrectly giving a compile time error
538        "recursive call could loop indefinitely" because it cannot analyze the
539        pattern in sufficient detail. The compile time test no longer happens when
540        PCRE is compiling a conditional subpattern, but actual runaway loops are
541        now caught at runtime (see 40 above).
542    
543    42. It seems that Perl allows any characters other than a closing parenthesis
544        to be part of the NAME in (*MARK:NAME) and other backtracking verbs. PCRE
545        has been changed to be the same.
546    
547    43. Updated configure.ac to put in more quoting round AC_LANG_PROGRAM etc. so
548        as not to get warnings when autogen.sh is called. Also changed
549        AC_PROG_LIBTOOL (deprecated) to LT_INIT (the current macro).
550    
551    44. To help people who use pcregrep to scan files containing exceedingly long
552        lines, the following changes have been made:
553    
554        (a) The default value of the buffer size parameter has been increased from
555            8K to 20K. (The actual buffer used is three times this size.)
556    
557        (b) The default can be changed by ./configure --with-pcregrep-bufsize when
558            PCRE is built.
559    
560        (c) A --buffer-size=n option has been added to pcregrep, to allow the size
561            to be set at run time.
562    
563        (d) Numerical values in pcregrep options can be followed by K or M, for
564            example --buffer-size=50K.
565    
566        (e) If a line being scanned overflows pcregrep's buffer, an error is now
567            given and the return code is set to 2.
568    
569    45. Add a pointer to the latest mark to the callout data block.
570    
571    46. The pattern /.(*F)/, when applied to "abc" with PCRE_PARTIAL_HARD, gave a
572        partial match of an empty string instead of no match. This was specific to
573        the use of ".".
574    
575    47. The pattern /f.*/8s, when applied to "for" with PCRE_PARTIAL_HARD, gave a
576        complete match instead of a partial match. This bug was dependent on both
577        the PCRE_UTF8 and PCRE_DOTALL options being set.
578    
579    48. For a pattern such as /\babc|\bdef/ pcre_study() was failing to set up the
580        starting byte set, because \b was not being ignored.
581    
582    
583    Version 8.12 15-Jan-2011
584    ------------------------
585    
586    1.  Fixed some typos in the markup of the man pages, and wrote a script that
587        checks for such things as part of the documentation building process.
588    
589    2.  On a big-endian 64-bit system, pcregrep did not correctly process the
590        --match-limit and --recursion-limit options (added for 8.11). In
591        particular, this made one of the standard tests fail. (The integer value
592        went into the wrong half of a long int.)
593    
594    3.  If the --colour option was given to pcregrep with -v (invert match), it
595        did strange things, either producing crazy output, or crashing. It should,
596        of course, ignore a request for colour when reporting lines that do not
597        match.
598    
599    4.  Another pcregrep bug caused similar problems if --colour was specified with
600        -M (multiline) and the pattern match finished with a line ending.
601    
602    5.  In pcregrep, when a pattern that ended with a literal newline sequence was
603        matched in multiline mode, the following line was shown as part of the
604        match. This seems wrong, so I have changed it.
605    
606    6.  Another pcregrep bug in multiline mode, when --colour was specified, caused
607        the check for further matches in the same line (so they could be coloured)
608        to overrun the end of the current line. If another match was found, it was
609        incorrectly shown (and then shown again when found in the next line).
610    
611    7.  If pcregrep was compiled under Windows, there was a reference to the
612        function pcregrep_exit() before it was defined. I am assuming this was
613        the cause of the "error C2371: 'pcregrep_exit' : redefinition;" that was
614        reported by a user. I've moved the definition above the reference.
615    
616    
617    Version 8.11 10-Dec-2010
618    ------------------------
619    
620    1.  (*THEN) was not working properly if there were untried alternatives prior
621        to it in the current branch. For example, in ((a|b)(*THEN)(*F)|c..) it
622        backtracked to try for "b" instead of moving to the next alternative branch
623        at the same level (in this case, to look for "c"). The Perl documentation
624        is clear that when (*THEN) is backtracked onto, it goes to the "next
625        alternative in the innermost enclosing group".
626    
627    2.  (*COMMIT) was not overriding (*THEN), as it does in Perl. In a pattern
628        such as   (A(*COMMIT)B(*THEN)C|D)  any failure after matching A should
629        result in overall failure. Similarly, (*COMMIT) now overrides (*PRUNE) and
630        (*SKIP), (*SKIP) overrides (*PRUNE) and (*THEN), and (*PRUNE) overrides
631        (*THEN).
632    
633    3.  If \s appeared in a character class, it removed the VT character from
634        the class, even if it had been included by some previous item, for example
635        in [\x00-\xff\s]. (This was a bug related to the fact that VT is not part
636        of \s, but is part of the POSIX "space" class.)
637    
638    4.  A partial match never returns an empty string (because you can always
639        match an empty string at the end of the subject); however the checking for
640        an empty string was starting at the "start of match" point. This has been
641        changed to the "earliest inspected character" point, because the returned
642        data for a partial match starts at this character. This means that, for
643        example, /(?<=abc)def/ gives a partial match for the subject "abc"
644        (previously it gave "no match").
645    
646    5.  Changes have been made to the way PCRE_PARTIAL_HARD affects the matching
647        of $, \z, \Z, \b, and \B. If the match point is at the end of the string,
648        previously a full match would be given. However, setting PCRE_PARTIAL_HARD
649        has an implication that the given string is incomplete (because a partial
650        match is preferred over a full match). For this reason, these items now
651        give a partial match in this situation. [Aside: previously, the one case
652        /t\b/ matched against "cat" with PCRE_PARTIAL_HARD set did return a partial
653        match rather than a full match, which was wrong by the old rules, but is
654        now correct.]
655    
656    6.  There was a bug in the handling of #-introduced comments, recognized when
657        PCRE_EXTENDED is set, when PCRE_NEWLINE_ANY and PCRE_UTF8 were also set.
658        If a UTF-8 multi-byte character included the byte 0x85 (e.g. +U0445, whose
659        UTF-8 encoding is 0xd1,0x85), this was misinterpreted as a newline when
660        scanning for the end of the comment. (*Character* 0x85 is an "any" newline,
661        but *byte* 0x85 is not, in UTF-8 mode). This bug was present in several
662        places in pcre_compile().
663    
664    7.  Related to (6) above, when pcre_compile() was skipping #-introduced
665        comments when looking ahead for named forward references to subpatterns,
666        the only newline sequence it recognized was NL. It now handles newlines
667        according to the set newline convention.
668    
669    8.  SunOS4 doesn't have strerror() or strtoul(); pcregrep dealt with the
670        former, but used strtoul(), whereas pcretest avoided strtoul() but did not
671        cater for a lack of strerror(). These oversights have been fixed.
672    
673    9.  Added --match-limit and --recursion-limit to pcregrep.
674    
675    10. Added two casts needed to build with Visual Studio when NO_RECURSE is set.
676    
677    11. When the -o option was used, pcregrep was setting a return code of 1, even
678        when matches were found, and --line-buffered was not being honoured.
679    
680    12. Added an optional parentheses number to the -o and --only-matching options
681        of pcregrep.
682    
683    13. Imitating Perl's /g action for multiple matches is tricky when the pattern
684        can match an empty string. The code to do it in pcretest and pcredemo
685        needed fixing:
686    
687        (a) When the newline convention was "crlf", pcretest got it wrong, skipping
688            only one byte after an empty string match just before CRLF (this case
689            just got forgotten; "any" and "anycrlf" were OK).
690    
691        (b) The pcretest code also had a bug, causing it to loop forever in UTF-8
692            mode when an empty string match preceded an ASCII character followed by
693            a non-ASCII character. (The code for advancing by one character rather
694            than one byte was nonsense.)
695    
696        (c) The pcredemo.c sample program did not have any code at all to handle
697            the cases when CRLF is a valid newline sequence.
698    
699    14. Neither pcre_exec() nor pcre_dfa_exec() was checking that the value given
700        as a starting offset was within the subject string. There is now a new
701        error, PCRE_ERROR_BADOFFSET, which is returned if the starting offset is
702        negative or greater than the length of the string. In order to test this,
703        pcretest is extended to allow the setting of negative starting offsets.
704    
705    15. In both pcre_exec() and pcre_dfa_exec() the code for checking that the
706        starting offset points to the beginning of a UTF-8 character was
707        unnecessarily clumsy. I tidied it up.
708    
709    16. Added PCRE_ERROR_SHORTUTF8 to make it possible to distinguish between a
710        bad UTF-8 sequence and one that is incomplete when using PCRE_PARTIAL_HARD.
711    
712    17. Nobody had reported that the --include_dir option, which was added in
713        release 7.7 should have been called --include-dir (hyphen, not underscore)
714        for compatibility with GNU grep. I have changed it to --include-dir, but
715        left --include_dir as an undocumented synonym, and the same for
716        --exclude-dir, though that is not available in GNU grep, at least as of
717        release 2.5.4.
718    
719    18. At a user's suggestion, the macros GETCHAR and friends (which pick up UTF-8
720        characters from a string of bytes) have been redefined so as not to use
721        loops, in order to improve performance in some environments. At the same
722        time, I abstracted some of the common code into auxiliary macros to save
723        repetition (this should not affect the compiled code).
724    
725    19. If \c was followed by a multibyte UTF-8 character, bad things happened. A
726        compile-time error is now given if \c is not followed by an ASCII
727        character, that is, a byte less than 128. (In EBCDIC mode, the code is
728        different, and any byte value is allowed.)
729    
730    20. Recognize (*NO_START_OPT) at the start of a pattern to set the PCRE_NO_
731        START_OPTIMIZE option, which is now allowed at compile time - but just
732        passed through to pcre_exec() or pcre_dfa_exec(). This makes it available
733        to pcregrep and other applications that have no direct access to PCRE
734        options. The new /Y option in pcretest sets this option when calling
735        pcre_compile().
736    
737    21. Change 18 of release 8.01 broke the use of named subpatterns for recursive
738        back references. Groups containing recursive back references were forced to
739        be atomic by that change, but in the case of named groups, the amount of
740        memory required was incorrectly computed, leading to "Failed: internal
741        error: code overflow". This has been fixed.
742    
743    22. Some patches to pcre_stringpiece.h, pcre_stringpiece_unittest.cc, and
744        pcretest.c, to avoid build problems in some Borland environments.
745    
746    
747    Version 8.10 25-Jun-2010
748    ------------------------
749    
750    1.  Added support for (*MARK:ARG) and for ARG additions to PRUNE, SKIP, and
751        THEN.
752    
753    2.  (*ACCEPT) was not working when inside an atomic group.
754    
755    3.  Inside a character class, \B is treated as a literal by default, but
756        faulted if PCRE_EXTRA is set. This mimics Perl's behaviour (the -w option
757        causes the error). The code is unchanged, but I tidied the documentation.
758    
759    4.  Inside a character class, PCRE always treated \R and \X as literals,
760        whereas Perl faults them if its -w option is set. I have changed PCRE so
761        that it faults them when PCRE_EXTRA is set.
762    
763    5.  Added support for \N, which always matches any character other than
764        newline. (It is the same as "." when PCRE_DOTALL is not set.)
765    
766    6.  When compiling pcregrep with newer versions of gcc which may have
767        FORTIFY_SOURCE set, several warnings "ignoring return value of 'fwrite',
768        declared with attribute warn_unused_result" were given. Just casting the
769        result to (void) does not stop the warnings; a more elaborate fudge is
770        needed. I've used a macro to implement this.
771    
772    7.  Minor change to pcretest.c to avoid a compiler warning.
773    
774    8.  Added four artifical Unicode properties to help with an option to make
775        \s etc use properties (see next item). The new properties are: Xan
776        (alphanumeric), Xsp (Perl space), Xps (POSIX space), and Xwd (word).
777    
778    9.  Added PCRE_UCP to make \b, \d, \s, \w, and certain POSIX character classes
779        use Unicode properties. (*UCP) at the start of a pattern can be used to set
780        this option. Modified pcretest to add /W to test this facility. Added
781        REG_UCP to make it available via the POSIX interface.
782    
783    10. Added --line-buffered to pcregrep.
784    
785    11. In UTF-8 mode, if a pattern that was compiled with PCRE_CASELESS was
786        studied, and the match started with a letter with a code point greater than
787        127 whose first byte was different to the first byte of the other case of
788        the letter, the other case of this starting letter was not recognized
789        (#976).
790    
791    12. If a pattern that was studied started with a repeated Unicode property
792        test, for example, \p{Nd}+, there was the theoretical possibility of
793        setting up an incorrect bitmap of starting bytes, but fortunately it could
794        not have actually happened in practice until change 8 above was made (it
795        added property types that matched character-matching opcodes).
796    
797    13. pcre_study() now recognizes \h, \v, and \R when constructing a bit map of
798        possible starting bytes for non-anchored patterns.
799    
800    14. Extended the "auto-possessify" feature of pcre_compile(). It now recognizes
801        \R, and also a number of cases that involve Unicode properties, both
802        explicit and implicit when PCRE_UCP is set.
803    
804    15. If a repeated Unicode property match (e.g. \p{Lu}*) was used with non-UTF-8
805        input, it could crash or give wrong results if characters with values
806        greater than 0xc0 were present in the subject string. (Detail: it assumed
807        UTF-8 input when processing these items.)
808    
809    16. Added a lot of (int) casts to avoid compiler warnings in systems where
810        size_t is 64-bit (#991).
811    
812    17. Added a check for running out of memory when PCRE is compiled with
813        --disable-stack-for-recursion (#990).
814    
815    18. If the last data line in a file for pcretest does not have a newline on
816        the end, a newline was missing in the output.
817    
818    19. The default pcre_chartables.c file recognizes only ASCII characters (values
819        less than 128) in its various bitmaps. However, there is a facility for
820        generating tables according to the current locale when PCRE is compiled. It
821        turns out that in some environments, 0x85 and 0xa0, which are Unicode space
822        characters, are recognized by isspace() and therefore were getting set in
823        these tables, and indeed these tables seem to approximate to ISO 8859. This
824        caused a problem in UTF-8 mode when pcre_study() was used to create a list
825        of bytes that can start a match. For \s, it was including 0x85 and 0xa0,
826        which of course cannot start UTF-8 characters. I have changed the code so
827        that only real ASCII characters (less than 128) and the correct starting
828        bytes for UTF-8 encodings are set for characters greater than 127 when in
829        UTF-8 mode. (When PCRE_UCP is set - see 9 above - the code is different
830        altogether.)
831    
832    20. Added the /T option to pcretest so as to be able to run tests with non-
833        standard character tables, thus making it possible to include the tests
834        used for 19 above in the standard set of tests.
835    
836    21. A pattern such as (?&t)(?#()(?(DEFINE)(?<t>a)) which has a forward
837        reference to a subpattern the other side of a comment that contains an
838        opening parenthesis caused either an internal compiling error, or a
839        reference to the wrong subpattern.
840    
841    
842    Version 8.02 19-Mar-2010
843    ------------------------
844    
845    1.  The Unicode data tables have been updated to Unicode 5.2.0.
846    
847    2.  Added the option --libs-cpp to pcre-config, but only when C++ support is
848        configured.
849    
850    3.  Updated the licensing terms in the pcregexp.pas file, as agreed with the
851        original author of that file, following a query about its status.
852    
853    4.  On systems that do not have stdint.h (e.g. Solaris), check for and include
854        inttypes.h instead. This fixes a bug that was introduced by change 8.01/8.
855    
856    5.  A pattern such as (?&t)*+(?(DEFINE)(?<t>.)) which has a possessive
857        quantifier applied to a forward-referencing subroutine call, could compile
858        incorrect code or give the error "internal error: previously-checked
859        referenced subpattern not found".
860    
861    6.  Both MS Visual Studio and Symbian OS have problems with initializing
862        variables to point to external functions. For these systems, therefore,
863        pcre_malloc etc. are now initialized to local functions that call the
864        relevant global functions.
865    
866    7.  There were two entries missing in the vectors called coptable and poptable
867        in pcre_dfa_exec.c. This could lead to memory accesses outsize the vectors.
868        I've fixed the data, and added a kludgy way of testing at compile time that
869        the lengths are correct (equal to the number of opcodes).
870    
871    8.  Following on from 7, I added a similar kludge to check the length of the
872        eint vector in pcreposix.c.
873    
874    9.  Error texts for pcre_compile() are held as one long string to avoid too
875        much relocation at load time. To find a text, the string is searched,
876        counting zeros. There was no check for running off the end of the string,
877        which could happen if a new error number was added without updating the
878        string.
879    
880    10. \K gave a compile-time error if it appeared in a lookbehind assersion.
881    
882    11. \K was not working if it appeared in an atomic group or in a group that
883        was called as a "subroutine", or in an assertion. Perl 5.11 documents that
884        \K is "not well defined" if used in an assertion. PCRE now accepts it if
885        the assertion is positive, but not if it is negative.
886    
887    12. Change 11 fortuitously reduced the size of the stack frame used in the
888        "match()" function of pcre_exec.c by one pointer. Forthcoming
889        implementation of support for (*MARK) will need an extra pointer on the
890        stack; I have reserved it now, so that the stack frame size does not
891        decrease.
892    
893    13. A pattern such as (?P<L1>(?P<L2>0)|(?P>L2)(?P>L1)) in which the only other
894        item in branch that calls a recursion is a subroutine call - as in the
895        second branch in the above example - was incorrectly given the compile-
896        time error "recursive call could loop indefinitely" because pcre_compile()
897        was not correctly checking the subroutine for matching a non-empty string.
898    
899    14. The checks for overrunning compiling workspace could trigger after an
900        overrun had occurred. This is a "should never occur" error, but it can be
901        triggered by pathological patterns such as hundreds of nested parentheses.
902        The checks now trigger 100 bytes before the end of the workspace.
903    
904    15. Fix typo in configure.ac: "srtoq" should be "strtoq".
905    
906    
907    Version 8.01 19-Jan-2010
908    ------------------------
909    
910    1.  If a pattern contained a conditional subpattern with only one branch (in
911        particular, this includes all (*DEFINE) patterns), a call to pcre_study()
912        computed the wrong minimum data length (which is of course zero for such
913        subpatterns). This could cause incorrect "no match" results.
914    
915    2.  For patterns such as (?i)a(?-i)b|c where an option setting at the start of
916      the pattern is reset in the first branch, pcre_compile() failed with      the pattern is reset in the first branch, pcre_compile() failed with
917      "internal error: code overflow at offset...". This happened only when      "internal error: code overflow at offset...". This happened only when
918      the reset was to the original external option setting. (An optimization      the reset was to the original external option setting. (An optimization
919      abstracts leading options settings into an external setting, which was the      abstracts leading options settings into an external setting, which was the
920      cause of this.)      cause of this.)
921    
922    3.  A pattern such as ^(?!a(*SKIP)b) where a negative assertion contained one
923        of the verbs SKIP, PRUNE, or COMMIT, did not work correctly. When the
924        assertion pattern did not match (meaning that the assertion was true), it
925        was incorrectly treated as false if the SKIP had been reached during the
926        matching. This also applied to assertions used as conditions.
927    
928    4.  If an item that is not supported by pcre_dfa_exec() was encountered in an
929        assertion subpattern, including such a pattern used as a condition,
930        unpredictable results occurred, instead of the error return
931        PCRE_ERROR_DFA_UITEM.
932    
933    5.  The C++ GlobalReplace function was not working like Perl for the special
934        situation when an empty string is matched. It now does the fancy magic
935        stuff that is necessary.
936    
937    6.  In pcre_internal.h, obsolete includes to setjmp.h and stdarg.h have been
938        removed. (These were left over from very, very early versions of PCRE.)
939    
940    7.  Some cosmetic changes to the code to make life easier when compiling it
941        as part of something else:
942    
943        (a) Change DEBUG to PCRE_DEBUG.
944    
945        (b) In pcre_compile(), rename the member of the "branch_chain" structure
946            called "current" as "current_branch", to prevent a collision with the
947            Linux macro when compiled as a kernel module.
948    
949        (c) In pcre_study(), rename the function set_bit() as set_table_bit(), to
950            prevent a collision with the Linux macro when compiled as a kernel
951            module.
952    
953    8.  In pcre_compile() there are some checks for integer overflows that used to
954        cast potentially large values to (double). This has been changed to that
955        when building, a check for int64_t is made, and if it is found, it is used
956        instead, thus avoiding the use of floating point arithmetic. (There is no
957        other use of FP in PCRE.) If int64_t is not found, the fallback is to
958        double.
959    
960    9.  Added two casts to avoid signed/unsigned warnings from VS Studio Express
961        2005 (difference between two addresses compared to an unsigned value).
962    
963    10. Change the standard AC_CHECK_LIB test for libbz2 in configure.ac to a
964        custom one, because of the following reported problem in Windows:
965    
966          - libbz2 uses the Pascal calling convention (WINAPI) for the functions
967              under Win32.
968          - The standard autoconf AC_CHECK_LIB fails to include "bzlib.h",
969              therefore missing the function definition.
970          - The compiler thus generates a "C" signature for the test function.
971          - The linker fails to find the "C" function.
972          - PCRE fails to configure if asked to do so against libbz2.
973    
974    11. When running libtoolize from libtool-2.2.6b as part of autogen.sh, these
975        messages were output:
976    
977          Consider adding `AC_CONFIG_MACRO_DIR([m4])' to configure.ac and
978          rerunning libtoolize, to keep the correct libtool macros in-tree.
979          Consider adding `-I m4' to ACLOCAL_AMFLAGS in Makefile.am.
980    
981        I have done both of these things.
982    
983    12. Although pcre_dfa_exec() does not use nearly as much stack as pcre_exec()
984        most of the time, it *can* run out if it is given a pattern that contains a
985        runaway infinite recursion. I updated the discussion in the pcrestack man
986        page.
987    
988    13. Now that we have gone to the x.xx style of version numbers, the minor
989        version may start with zero. Using 08 or 09 is a bad idea because users
990        might check the value of PCRE_MINOR in their code, and 08 or 09 may be
991        interpreted as invalid octal numbers. I've updated the previous comment in
992        configure.ac, and also added a check that gives an error if 08 or 09 are
993        used.
994    
995    14. Change 8.00/11 was not quite complete: code had been accidentally omitted,
996        causing partial matching to fail when the end of the subject matched \W
997        in a UTF-8 pattern where \W was quantified with a minimum of 3.
998    
999    15. There were some discrepancies between the declarations in pcre_internal.h
1000        of _pcre_is_newline(), _pcre_was_newline(), and _pcre_valid_utf8() and
1001        their definitions. The declarations used "const uschar *" and the
1002        definitions used USPTR. Even though USPTR is normally defined as "const
1003        unsigned char *" (and uschar is typedeffed as "unsigned char"), it was
1004        reported that: "This difference in casting confuses some C++ compilers, for
1005        example, SunCC recognizes above declarations as different functions and
1006        generates broken code for hbpcre." I have changed the declarations to use
1007        USPTR.
1008    
1009    16. GNU libtool is named differently on some systems. The autogen.sh script now
1010        tries several variants such as glibtoolize (MacOSX) and libtoolize1x
1011        (FreeBSD).
1012    
1013    17. Applied Craig's patch that fixes an HP aCC compile error in pcre 8.00
1014        (strtoXX undefined when compiling pcrecpp.cc). The patch contains this
1015        comment: "Figure out how to create a longlong from a string: strtoll and
1016        equivalent. It's not enough to call AC_CHECK_FUNCS: hpux has a strtoll, for
1017        instance, but it only takes 2 args instead of 3!"
1018    
1019    18. A subtle bug concerned with back references has been fixed by a change of
1020        specification, with a corresponding code fix. A pattern such as
1021        ^(xa|=?\1a)+$ which contains a back reference inside the group to which it
1022        refers, was giving matches when it shouldn't. For example, xa=xaaa would
1023        match that pattern. Interestingly, Perl (at least up to 5.11.3) has the
1024        same bug. Such groups have to be quantified to be useful, or contained
1025        inside another quantified group. (If there's no repetition, the reference
1026        can never match.) The problem arises because, having left the group and
1027        moved on to the rest of the pattern, a later failure that backtracks into
1028        the group uses the captured value from the final iteration of the group
1029        rather than the correct earlier one. I have fixed this in PCRE by forcing
1030        any group that contains a reference to itself to be an atomic group; that
1031        is, there cannot be any backtracking into it once it has completed. This is
1032        similar to recursive and subroutine calls.
1033    
1034    
1035  Version 8.00 19-Oct-09  Version 8.00 19-Oct-09
1036  ----------------------  ----------------------

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