Contents of /code/trunk/maint/README

MAINTENANCE README FOR PCRE
===========================

The files in the "maint" directory of the PCRE source contain data, scripts,
and programs that are used for the maintenance of PCRE, but which do not form
part of the PCRE distribution tarballs. This document describes these files and
also contains some notes for maintainers. Its contents are:

  Files in the maint directory
  Updating to a new Unicode release
  Preparing for a PCRE release
  Making a PCRE release
  Long-term ideas (wish list)


Files in the maint directory
============================

---------------- This file is now OBSOLETE and no longer used ----------------
Builducptable    A Perl script that creates the contents of the ucptable.h file
                 from two Unicode data files, which themselves are downloaded
                 from the Unicode web site. Run this script in the "maint"
                 directory.
---------------- This file is now OBSOLETE and no longer used ----------------

GenerateUtt.py   A Python script to generate part of the pcre_tables.c file
                 that contains Unicode script names in a long string with
                 offsets, which is tedious to maintain by hand.

ManyConfigTests  A shell script that runs "configure, make, test" a number of
                 times with different configuration settings.

MultiStage2.py   A Python script that generates the file pcre_ucd.c from three
                 Unicode data tables, which are themselves downloaded from the
                 Unicode web site. Run this script in the "maint" directory.
                 The generated file contains the tables for a 2-stage lookup
                 of Unicode properties.
                 
pcre_chartables.c.non-standard
                 This is a set of character tables that came from a Windows
                 system. It has characters greater than 128 that are set as
                 spaces, amongst other things. I kept it so that it can be
                 used for testing from time to time.    

README           This file.

Unicode.tables   The files in this directory, DerivedGeneralCategory.txt,
                 Scripts.txt and UnicodeData.txt, were downloaded from the
                 Unicode web site. They contain information about Unicode
                 characters and scripts.

ucptest.c        A short C program for testing the Unicode property macros
                 that do lookups in the pcre_ucd.c data, mainly useful after
                 rebuilding the Unicode property table. Compile and run this in
                 the "maint" directory (see comments at its head).

ucptestdata      A directory containing two files, testinput1 and testoutput1,
                 to use in conjunction with the ucptest program.

utf8.c           A short, freestanding C program for converting a Unicode code
                 point into a sequence of bytes in the UTF-8 encoding, and vice
                 versa. If its argument is a hex number such as 0x1234, it
                 outputs a list of the equivalent UTF-8 bytes. If its argument
                 is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
                 treats them as a UTF-8 character and outputs the equivalent
                 code point in hex.


Updating to a new Unicode release
=================================

When there is a new release of Unicode, the files in Unicode.tables must be
refreshed from the web site. If the new version of Unicode adds new character
scripts, the source file ucp.h and both the MultiStage2.py and the
GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
can be run to generate a new version of pcre_ucd.c, and GenerateUtt.py can be
run to generate the tricky tables for inclusion in pcre_tables.c.

If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
the cause is usually a missing (or misspelt) name in the list of scripts. I
couldn't find a straightforward list of scripts on the Unicode site, but
there's a useful Wikipedia page that list them, and notes the Unicode version
in which they were introduced:

http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts

The ucptest program can be compiled and used to check that the new tables in
pcre_ucd.c work properly, using the data files in ucptestdata to check a number
of test characters. The source file ucptest.c must be updated whenever new
Unicode script names are added.

Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
of Unicode script names.


Preparing for a PCRE release
============================

This section contains a checklist of things that I consult before building a
distribution for a new release.

. Ensure that the version number and version date are correct in configure.ac.

. If new build options have been added, ensure that they are added to the CMake
  files as well as to the autoconf files.

. Run ./autogen.sh to ensure everything is up-to-date.

. Compile and test with many different config options, and combinations of
  options. The maint/ManyConfigTests script now encapsulates this testing.

. Run perltest.pl on the test data for tests 1, 4, 6, and 11. The first two can
  be run with Perl 5.8 or >= 5.10; the last two require Perl >= 5.10. The
  output should match the PCRE test output, apart from the version
  identification at the start of each test. The other tests are not
  Perl-compatible (they use various PCRE-specific features or options).

. Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
  valgrind", though that takes quite a long time.

. It may also useful to test with Electric Fence, though the fact that it
  grumbles for missing free() calls can be a nuisance. (A missing free() in
  pcretest is hardly a big problem.) To build with EF, use:

    LIBS='/usr/lib/libefence.a -lpthread' with ./configure.

  Then all normal runs use it to check for buffer overflow. Also run everything
  with:

    EF_PROTECT_BELOW=1 <whatever>

  because there have been problems with lookbehinds that looked too far.

. Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
  HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
  used" warnings for the modules in which there is no call to memmove(). These
  can be ignored.

. Documentation: check AUTHORS, COPYING, ChangeLog (check version and date),
  INSTALL, LICENCE, NEWS (check version and date), NON-UNIX-USE, and README.
  Many of these won't need changing, but over the long term things do change.

. Man pages: Check all man pages for \ not followed by e or f or " because
  that indicates a markup error. However, there is one exception: pcredemo.3,
  which is created from the pcredemo.c program. It contains three instances
  of \\n.

. When the release is built, test it on a number of different operating
  systems if possible, and using different compilers as well. For example,
  on Solaris it is helpful to test using Sun's cc compiler as a change from
  gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
  needs -S 64 for pcretest to increase the stack size for test 2.


Making a PCRE release
=====================

Run PrepareRelease and commit the files that it changes (by removing trailing
spaces). Then run "make distcheck" to create the tarballs and the zipball.
Double-check with "svn status", then create an SVN tagged copy:

  svn copy svn://vcs.exim.org/pcre/code/trunk \
           svn://vcs.exim.org/pcre/code/tags/pcre-8.xx

Don't forget to update Freshmeat when the new release is out, and to tell
webmaster@pcre.org and the mailing list. Also, update the list of version
numbers in Bugzilla (edit products).


Future ideas (wish list)
========================

This section records a list of ideas so that they do not get forgotten. They
vary enormously in their usefulness and potential for implementation. Some are
very sensible; some are rather wacky. Some have been on this list for years;
others are relatively new.

. Optimization

  There are always ideas for new optimizations so as to speed up pattern
  matching. Most of them try to save work by recognizing a non-match without
  having to scan all the possibilities. These are some that I've recorded:

  * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
    slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
    OTOH, this is pathological - the user could easily fix it.

  * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
    to have little effect, and maybe makes things worse.

  * "Ends with literal string" - note that a single character doesn't gain much
    over the existing "required byte" (reqbyte) feature that just remembers one
    byte.

  * These probably need to go in pcre_study():

    o Remember an initial string rather than just 1 char?

    o A required byte from alternatives - not just the last char, but an
      earlier one if common to all alternatives.

    o Friedl contains other ideas.

  * pcre_study() does not set initial byte flags for Unicode property types
    such as \p; I don't know how much benefit there would be for, for example,
    setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
    \p{N}.

  * There is scope for more "auto-possessifying" in connection with \p and \P.

. If Perl gets to a consistent state over the settings of capturing sub-
  patterns inside repeats, see if we can match it. One example of the
  difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
  leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
  because I think it needs much more state to be remembered.

. Perl 6 will be a revolution. Is it a revolution too far for PCRE?

. Unicode

  * A different approach to Unicode might be to use a typedef to do everything
    in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
    new typedef to distinguish data from bits of compiled pattern that are in
    bytes, I think. There would need to be conversion functions in and out. I
    don't think this is particularly trivial - and anyway, Unicode now has
    characters that need more than 16 bits, so is this at all sensible?

  * There has been a request for direct support of 16-bit characters and
    UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
    is this worth it at all? One possible way of handling 16-bit characters
    would be to "load" them in the same way that UTF-8 characters are loaded.

. Allow errorptr and erroroffset to be NULL. I don't like this idea.

. Line endings:

  * Option to use NUL as a line terminator in subject strings. This could now
    be done relatively easily since the extension to support LF, CR, and CRLF.
    If it is done, a suitable option for pcregrep is also required.

. Option to provide the pattern with a length instead of with a NUL terminator.
  This affects quite a few places in the code and is not trivial.

. Catch SIGSEGV for stack overflows?

. A feature to suspend a match via a callout was once requested.

. Option to convert results into character offsets and character lengths.

. Option for pcregrep to scan only the start of a file. I am not keen - this is
  the job of "head".

. A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
  preceded by a blank line, instead of adding it to every matched line, and (b)
  support --outputfile=name.

. Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.

. Add a user pointer to pcre_malloc/free functions -- some option would be
  needed to retain backward compatibility.

. Define a union for the results from pcre_fullinfo().

. Provide a "random access to the subject" facility so that the way in which it
  is stored is independent of PCRE. For efficiency, it probably isn't possible
  to switch this dynamically. It would have to be specified when PCRE was
  compiled. PCRE would then call a function every time it wanted a character.

. Wild thought: the ability to compile from PCRE's internal byte code to a real
  FSM and a very fast (third) matcher to process the result. There would be
  even more restrictions than for pcre_dfa_exec(), however. This is not easy.

. Should pcretest have some private locale data, to avoid relying on the
  available locales for the test data, since different OS have different ideas?
  This won't be as thorough a test, but perhaps that doesn't really matter.

. pcregrep: add -rs for a sorted recurse? Having to store file names and sort
  them will of course slow it down.

. Someone suggested --disable-callout to save code space when callouts are
  never wanted. This seems rather marginal.

. Check names that consist entirely of digits: PCRE allows, but do Perl and
  Python, etc?

. A user suggested a parameter to limit the length of string matched, for
  example if the parameter is N, the current match should fail if the matched
  substring exceeds N. This could apply to both match functions. The value
  could be a new field in the extra block.

. Callouts with arguments: (?Cn:ARG) for instance.

. A user is going to supply a patch to generalize the API for user-specific
  memory allocation so that it is more flexible in threaded environments. This
  was promised a long time ago, and never appeared...

. Write a function that generates random matching strings for a compiled regex.

. Write a wrapper to maintain a structure with specified runtime parameters,
  such as recurse limit, and pass these to PCRE each time it is called. Also
  maybe malloc and free. A user sent a prototype.

. Pcregrep: an option to specify the output line separator, either as a string
  or select from a fixed list. This is not dead easy, because at the moment it
  outputs whatever is in the input file.

. Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
  non-thread-safe patch showed that this can help performance for patterns
  where there are many alternatives. However, a simple thread-safe
  implementation that I tried made things worse in many simple cases, so this
  is not an obviously good thing.

. Make the longest lookbehind available via pcre_fullinfo(). This is not
  straightforward because lookbehinds can be nested inside lookbehinds. This
  case will have to be identified, and the amounts added. This should then give
  the maximum possible lookbehind length. The reason for wanting this is to
  help when implementing multi-segment matching using pcre_exec() with partial
  matching and overlapping segments.

. PCRE cannot at present distinguish between subpatterns with different names,
  but the same number (created by the use of ?|). In order to do so, a way of
  remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
  Now that (*MARK) has been implemented, it can perhaps be used as a way round
  this problem.

. Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
  "something" and the the #ifdef appears only in one place, in "something".

Philip Hazel
Email local part: ph10
Email domain: cam.ac.uk
Last updated: 03 June 2010
1	ph10	122	MAINTENANCE README FOR PCRE
2	ph10	507	===========================
3	ph10	122
4	ph10	181	The files in the "maint" directory of the PCRE source contain data, scripts,
5	ph10	122	and programs that are used for the maintenance of PCRE, but which do not form
6	ph10	181	part of the PCRE distribution tarballs. This document describes these files and
7	ph10	122	also contains some notes for maintainers. Its contents are:
8	ph10	97
9	ph10	122	Files in the maint directory
10			Updating to a new Unicode release
11			Preparing for a PCRE release
12			Making a PCRE release
13	ph10	181	Long-term ideas (wish list)
14	ph10	122
15
16			Files in the maint directory
17	ph10	507	============================
18	ph10	122
19	ph10	507	---------------- This file is now OBSOLETE and no longer used ----------------
20	ph10	129	Builducptable A Perl script that creates the contents of the ucptable.h file
21			from two Unicode data files, which themselves are downloaded
22			from the Unicode web site. Run this script in the "maint"
23			directory.
24	ph10	507	---------------- This file is now OBSOLETE and no longer used ----------------
25	ph10	181
26	ph10	351	GenerateUtt.py A Python script to generate part of the pcre_tables.c file
27			that contains Unicode script names in a long string with
28	ph10	535	offsets, which is tedious to maintain by hand.
29	ph10	351
30	ph10	129	ManyConfigTests A shell script that runs "configure, make, test" a number of
31			times with different configuration settings.
32	ph10	535
33	ph10	350	MultiStage2.py A Python script that generates the file pcre_ucd.c from three
34			Unicode data tables, which are themselves downloaded from the
35	ph10	535	Unicode web site. Run this script in the "maint" directory.
36	ph10	350	The generated file contains the tables for a 2-stage lookup
37	ph10	535	of Unicode properties.
38	ph10	539
39			pcre_chartables.c.non-standard
40			This is a set of character tables that came from a Windows
41			system. It has characters greater than 128 that are set as
42			spaces, amongst other things. I kept it so that it can be
43			used for testing from time to time.
44	ph10	181
45	ph10	454	README This file.
46
47	ph10	535	Unicode.tables The files in this directory, DerivedGeneralCategory.txt,
48	ph10	350	Scripts.txt and UnicodeData.txt, were downloaded from the
49			Unicode web site. They contain information about Unicode
50			characters and scripts.
51	ph10	181
52	ph10	350	ucptest.c A short C program for testing the Unicode property macros
53			that do lookups in the pcre_ucd.c data, mainly useful after
54			rebuilding the Unicode property table. Compile and run this in
55	ph10	351	the "maint" directory (see comments at its head).
56	ph10	181
57	ph10	129	ucptestdata A directory containing two files, testinput1 and testoutput1,
58			to use in conjunction with the ucptest program.
59	ph10	181
60	ph10	129	utf8.c A short, freestanding C program for converting a Unicode code
61			point into a sequence of bytes in the UTF-8 encoding, and vice
62			versa. If its argument is a hex number such as 0x1234, it
63			outputs a list of the equivalent UTF-8 bytes. If its argument
64			is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
65			treats them as a UTF-8 character and outputs the equivalent
66			code point in hex.
67	ph10	97
68	ph10	181
69	ph10	122	Updating to a new Unicode release
70	ph10	507	=================================
71	ph10	122
72	ph10	181	When there is a new release of Unicode, the files in Unicode.tables must be
73	ph10	454	refreshed from the web site. If the new version of Unicode adds new character
74	ph10	352	scripts, the source file ucp.h and both the MultiStage2.py and the
75	ph10	454	GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
76			can be run to generate a new version of pcre_ucd.c, and GenerateUtt.py can be
77			run to generate the tricky tables for inclusion in pcre_tables.c.
78	ph10	122
79	ph10	491	If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
80	ph10	535	the cause is usually a missing (or misspelt) name in the list of scripts. I
81			couldn't find a straightforward list of scripts on the Unicode site, but
82			there's a useful Wikipedia page that list them, and notes the Unicode version
83	ph10	491	in which they were introduced:
84
85			http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts
86
87	ph10	454	The ucptest program can be compiled and used to check that the new tables in
88			pcre_ucd.c work properly, using the data files in ucptestdata to check a number
89	ph10	491	of test characters. The source file ucptest.c must be updated whenever new
90			Unicode script names are added.
91	ph10	122
92	ph10	535	Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
93	ph10	491	of Unicode script names.
94	ph10	351
95	ph10	491
96	ph10	122	Preparing for a PCRE release
97	ph10	507	============================
98	ph10	122
99			This section contains a checklist of things that I consult before building a
100			distribution for a new release.
101
102	ph10	454	. Ensure that the version number and version date are correct in configure.ac.
103	ph10	535
104	ph10	292	. If new build options have been added, ensure that they are added to the CMake
105	ph10	535	files as well as to the autoconf files.
106	ph10	122
107			. Run ./autogen.sh to ensure everything is up-to-date.
108
109	ph10	181	. Compile and test with many different config options, and combinations of
110	ph10	129	options. The maint/ManyConfigTests script now encapsulates this testing.
111	ph10	181
112	ph10	535	. Run perltest.pl on the test data for tests 1, 4, 6, and 11. The first two can
113			be run with Perl 5.8 or >= 5.10; the last two require Perl >= 5.10. The
114			output should match the PCRE test output, apart from the version
115			identification at the start of each test. The other tests are not
116			Perl-compatible (they use various PCRE-specific features or options).
117	ph10	122
118			. Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
119			valgrind", though that takes quite a long time.
120	ph10	181
121			. It may also useful to test with Electric Fence, though the fact that it
122			grumbles for missing free() calls can be a nuisance. (A missing free() in
123	ph10	122	pcretest is hardly a big problem.) To build with EF, use:
124	ph10	181
125	ph10	122	LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
126
127			Then all normal runs use it to check for buffer overflow. Also run everything
128			with:
129	ph10	181
130			EF_PROTECT_BELOW=1 <whatever>
131
132			because there have been problems with lookbehinds that looked too far.
133
134			. Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
135			HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
136	ph10	155	used" warnings for the modules in which there is no call to memmove(). These
137			can be ignored.
138	ph10	122
139	ph10	535	. Documentation: check AUTHORS, COPYING, ChangeLog (check version and date),
140	ph10	454	INSTALL, LICENCE, NEWS (check version and date), NON-UNIX-USE, and README.
141			Many of these won't need changing, but over the long term things do change.
142	ph10	181
143	ph10	122	. Man pages: Check all man pages for \ not followed by e or f or " because
144	ph10	535	that indicates a markup error. However, there is one exception: pcredemo.3,
145	ph10	507	which is created from the pcredemo.c program. It contains three instances
146	ph10	535	of \\n.
147	ph10	122
148	ph10	181	. When the release is built, test it on a number of different operating
149	ph10	155	systems if possible, and using different compilers as well. For example,
150			on Solaris it is helpful to test using Sun's cc compiler as a change from
151			gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
152			needs -S 64 for pcretest to increase the stack size for test 2.
153	ph10	122
154	ph10	155
155	ph10	122	Making a PCRE release
156	ph10	507	=====================
157	ph10	122
158			Run PrepareRelease and commit the files that it changes (by removing trailing
159	ph10	155	spaces). Then run "make distcheck" to create the tarballs and the zipball.
160	ph10	212	Double-check with "svn status", then create an SVN tagged copy:
161	ph10	122
162	ph10	212	svn copy svn://vcs.exim.org/pcre/code/trunk \
163	ph10	535	svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
164	ph10	212
165	ph10	122	Don't forget to update Freshmeat when the new release is out, and to tell
166	ph10	535	webmaster@pcre.org and the mailing list. Also, update the list of version
167	ph10	507	numbers in Bugzilla (edit products).
168	ph10	122
169
170			Future ideas (wish list)
171	ph10	507	========================
172	ph10	122
173			This section records a list of ideas so that they do not get forgotten. They
174	ph10	181	vary enormously in their usefulness and potential for implementation. Some are
175	ph10	122	very sensible; some are rather wacky. Some have been on this list for years;
176			others are relatively new.
177
178			. Optimization
179
180	ph10	181	There are always ideas for new optimizations so as to speed up pattern
181			matching. Most of them try to save work by recognizing a non-match without
182	ph10	122	having to scan all the possibilities. These are some that I've recorded:
183
184			* /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
185			slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
186	ph10	181	OTOH, this is pathological - the user could easily fix it.
187
188	ph10	122	* Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
189			to have little effect, and maybe makes things worse.
190	ph10	181
191			* "Ends with literal string" - note that a single character doesn't gain much
192	ph10	454	over the existing "required byte" (reqbyte) feature that just remembers one
193	ph10	122	byte.
194	ph10	181
195	ph10	535	* These probably need to go in pcre_study():
196	ph10	181
197	ph10	122	o Remember an initial string rather than just 1 char?
198	ph10	181
199	ph10	122	o A required byte from alternatives - not just the last char, but an
200			earlier one if common to all alternatives.
201	ph10	181
202	ph10	122	o Friedl contains other ideas.
203	ph10	535
204			* pcre_study() does not set initial byte flags for Unicode property types
205			such as \p; I don't know how much benefit there would be for, for example,
206			setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
207			\p{N}.
208
209			* There is scope for more "auto-possessifying" in connection with \p and \P.
210
211	ph10	122	. If Perl gets to a consistent state over the settings of capturing sub-
212			patterns inside repeats, see if we can match it. One example of the
213			difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
214			leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
215			because I think it needs much more state to be remembered.
216
217	ph10	181	. Perl 6 will be a revolution. Is it a revolution too far for PCRE?
218
219	ph10	122	. Unicode
220
221			* A different approach to Unicode might be to use a typedef to do everything
222			in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
223			new typedef to distinguish data from bits of compiled pattern that are in
224			bytes, I think. There would need to be conversion functions in and out. I
225			don't think this is particularly trivial - and anyway, Unicode now has
226			characters that need more than 16 bits, so is this at all sensible?
227	ph10	181
228	ph10	122	* There has been a request for direct support of 16-bit characters and
229			UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
230			is this worth it at all? One possible way of handling 16-bit characters
231			would be to "load" them in the same way that UTF-8 characters are loaded.
232	ph10	181
233	ph10	122	. Allow errorptr and erroroffset to be NULL. I don't like this idea.
234
235			. Line endings:
236
237			* Option to use NUL as a line terminator in subject strings. This could now
238			be done relatively easily since the extension to support LF, CR, and CRLF.
239	ph10	454	If it is done, a suitable option for pcregrep is also required.
240	ph10	181
241	ph10	122	. Option to provide the pattern with a length instead of with a NUL terminator.
242	ph10	454	This affects quite a few places in the code and is not trivial.
243	ph10	122
244	ph10	181	. Catch SIGSEGV for stack overflows?
245	ph10	122
246			. A feature to suspend a match via a callout was once requested.
247
248			. Option to convert results into character offsets and character lengths.
249
250	ph10	181	. Option for pcregrep to scan only the start of a file. I am not keen - this is
251	ph10	122	the job of "head".
252	ph10	181
253			. A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
254	ph10	122	preceded by a blank line, instead of adding it to every matched line, and (b)
255			support --outputfile=name.
256	ph10	181
257	ph10	454	. Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
258	ph10	122
259	ph10	181	. Add a user pointer to pcre_malloc/free functions -- some option would be
260	ph10	122	needed to retain backward compatibility.
261	ph10	181
262	ph10	122	. Define a union for the results from pcre_fullinfo().
263
264	ph10	181	. Provide a "random access to the subject" facility so that the way in which it
265			is stored is independent of PCRE. For efficiency, it probably isn't possible
266	ph10	122	to switch this dynamically. It would have to be specified when PCRE was
267			compiled. PCRE would then call a function every time it wanted a character.
268	ph10	181
269	ph10	122	. Wild thought: the ability to compile from PCRE's internal byte code to a real
270			FSM and a very fast (third) matcher to process the result. There would be
271			even more restrictions than for pcre_dfa_exec(), however. This is not easy.
272	ph10	181
273	ph10	122	. Should pcretest have some private locale data, to avoid relying on the
274			available locales for the test data, since different OS have different ideas?
275			This won't be as thorough a test, but perhaps that doesn't really matter.
276	ph10	181
277			. pcregrep: add -rs for a sorted recurse? Having to store file names and sort
278	ph10	122	them will of course slow it down.
279
280	ph10	181	. Someone suggested --disable-callout to save code space when callouts are
281			never wanted. This seems rather marginal.
282	ph10	535
283			. Check names that consist entirely of digits: PCRE allows, but do Perl and
284			Python, etc?
285
286			. A user suggested a parameter to limit the length of string matched, for
287			example if the parameter is N, the current match should fail if the matched
288			substring exceeds N. This could apply to both match functions. The value
289	ph10	372	could be a new field in the extra block.
290	ph10	535
291	ph10	372	. Callouts with arguments: (?Cn:ARG) for instance.
292	ph10	122
293	ph10	535	. A user is going to supply a patch to generalize the API for user-specific
294	ph10	507	memory allocation so that it is more flexible in threaded environments. This
295	ph10	454	was promised a long time ago, and never appeared...
296	ph10	535
297	ph10	454	. Write a function that generates random matching strings for a compiled regex.
298	ph10	372
299	ph10	535	. Write a wrapper to maintain a structure with specified runtime parameters,
300			such as recurse limit, and pass these to PCRE each time it is called. Also
301	ph10	454	maybe malloc and free. A user sent a prototype.
302	ph10	535
303			. Pcregrep: an option to specify the output line separator, either as a string
304			or select from a fixed list. This is not dead easy, because at the moment it
305	ph10	454	outputs whatever is in the input file.
306	ph10	535
307			. Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
308			non-thread-safe patch showed that this can help performance for patterns
309			where there are many alternatives. However, a simple thread-safe
310			implementation that I tried made things worse in many simple cases, so this
311	ph10	454	is not an obviously good thing.
312	ph10	535
313			. Make the longest lookbehind available via pcre_fullinfo(). This is not
314			straightforward because lookbehinds can be nested inside lookbehinds. This
315			case will have to be identified, and the amounts added. This should then give
316			the maximum possible lookbehind length. The reason for wanting this is to
317	ph10	454	help when implementing multi-segment matching using pcre_exec() with partial
318			matching and overlapping segments.
319	ph10	535
320	ph10	454	. PCRE cannot at present distinguish between subpatterns with different names,
321	ph10	535	but the same number (created by the use of ?\|). In order to do so, a way of
322	ph10	454	remembering which subpattern numbered n matched is needed. Bugzilla #760.
323	ph10	535	Now that (*MARK) has been implemented, it can perhaps be used as a way round
324			this problem.
325
326			. Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
327	ph10	507	"something" and the the #ifdef appears only in one place, in "something".
328	ph10	454
329	ph10	122	Philip Hazel
330			Email local part: ph10
331			Email domain: cam.ac.uk
332	ph10	535	Last updated: 03 June 2010