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 ----------------

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.  

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.

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, and the MultiStage2.py script can then be run to
generate a new version of pcre_ucd.c. The ucptest program can be used to check
that the resulting table works properly, using the data files in ucptestdata to
check a number of test characters.


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,
  ChangeLog, and NEWS.
  
. 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 and 4. The output should match
  the PCRE test output, apart from the version identification at the top. The
  other tests are not Perl-compatible (they use various special PCRE 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 date), INSTALL,
  LICENCE, NEWS (check 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.

. 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-7.x 

Don't forget to update Freshmeat when the new release is out, and to tell
webmaster@pcre.org and the mailing list.


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 saves one
    byte.

  * These probably need to go in 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 Minimum length of subject needed.

    o Friedl contains other ideas.

. 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

  * Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
    character classes. For the moment, I've chosen not to support this for
    backward compatibility, for speed, and because it would be messy to
    implement.

  * 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 this 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 probably affects quite a few places in the code.

. 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 > 7.

. 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? 

Philip Hazel
Email local part: ph10
Email domain: cam.ac.uk
Last updated: 02 July 2008
1	ph10	122	MAINTENANCE README FOR PCRE
2			---------------------------
3
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			----------------------------
18
19	ph10	350	----------------- 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	350	----------------- This file is now OBSOLETE and no longer used ----------------
25	ph10	181
26	ph10	129	ManyConfigTests A shell script that runs "configure, make, test" a number of
27			times with different configuration settings.
28	ph10	350
29			MultiStage2.py A Python script that generates the file pcre_ucd.c from three
30			Unicode data tables, which are themselves downloaded from the
31			Unicode web site. Run this script in the "maint" directory.
32			The generated file contains the tables for a 2-stage lookup
33			of Unicode properties.
34	ph10	181
35	ph10	350	Unicode.tables The files in this directory, DerivedGeneralCategory.txt,
36			Scripts.txt and UnicodeData.txt, were downloaded from the
37			Unicode web site. They contain information about Unicode
38			characters and scripts.
39	ph10	181
40	ph10	350	ucptest.c A short C program for testing the Unicode property macros
41			that do lookups in the pcre_ucd.c data, mainly useful after
42			rebuilding the Unicode property table. Compile and run this in
43			the "maint" directory.
44	ph10	181
45	ph10	129	ucptestdata A directory containing two files, testinput1 and testoutput1,
46			to use in conjunction with the ucptest program.
47	ph10	181
48	ph10	129	utf8.c A short, freestanding C program for converting a Unicode code
49			point into a sequence of bytes in the UTF-8 encoding, and vice
50			versa. If its argument is a hex number such as 0x1234, it
51			outputs a list of the equivalent UTF-8 bytes. If its argument
52			is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
53			treats them as a UTF-8 character and outputs the equivalent
54			code point in hex.
55	ph10	97
56	ph10	181
57	ph10	122	Updating to a new Unicode release
58			---------------------------------
59
60	ph10	181	When there is a new release of Unicode, the files in Unicode.tables must be
61	ph10	350	refreshed from the web site, and the MultiStage2.py script can then be run to
62			generate a new version of pcre_ucd.c. The ucptest program can be used to check
63	ph10	181	that the resulting table works properly, using the data files in ucptestdata to
64			check a number of test characters.
65	ph10	122
66
67			Preparing for a PCRE release
68			----------------------------
69
70			This section contains a checklist of things that I consult before building a
71			distribution for a new release.
72
73	ph10	155	. Ensure that the version number and version date are correct in configure.ac,
74			ChangeLog, and NEWS.
75	ph10	292
76			. If new build options have been added, ensure that they are added to the CMake
77			files as well as to the autoconf files.
78	ph10	122
79			. Run ./autogen.sh to ensure everything is up-to-date.
80
81	ph10	181	. Compile and test with many different config options, and combinations of
82	ph10	129	options. The maint/ManyConfigTests script now encapsulates this testing.
83	ph10	181
84	ph10	122	. Run perltest.pl on the test data for tests 1 and 4. The output should match
85	ph10	181	the PCRE test output, apart from the version identification at the top. The
86	ph10	122	other tests are not Perl-compatible (they use various special PCRE options).
87
88			. Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
89			valgrind", though that takes quite a long time.
90	ph10	181
91			. It may also useful to test with Electric Fence, though the fact that it
92			grumbles for missing free() calls can be a nuisance. (A missing free() in
93	ph10	122	pcretest is hardly a big problem.) To build with EF, use:
94	ph10	181
95	ph10	122	LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
96
97			Then all normal runs use it to check for buffer overflow. Also run everything
98			with:
99	ph10	181
100			EF_PROTECT_BELOW=1 <whatever>
101
102			because there have been problems with lookbehinds that looked too far.
103
104			. Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
105			HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
106	ph10	155	used" warnings for the modules in which there is no call to memmove(). These
107			can be ignored.
108	ph10	122
109	ph10	181	. Documentation: check AUTHORS, COPYING, ChangeLog (check date), INSTALL,
110			LICENCE, NEWS (check date), NON-UNIX-USE, and README. Many of these won't
111	ph10	122	need changing, but over the long term things do change.
112	ph10	181
113	ph10	122	. Man pages: Check all man pages for \ not followed by e or f or " because
114			that indicates a markup error.
115
116	ph10	181	. When the release is built, test it on a number of different operating
117	ph10	155	systems if possible, and using different compilers as well. For example,
118			on Solaris it is helpful to test using Sun's cc compiler as a change from
119			gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
120			needs -S 64 for pcretest to increase the stack size for test 2.
121	ph10	122
122	ph10	155
123	ph10	122	Making a PCRE release
124			---------------------
125
126			Run PrepareRelease and commit the files that it changes (by removing trailing
127	ph10	155	spaces). Then run "make distcheck" to create the tarballs and the zipball.
128	ph10	212	Double-check with "svn status", then create an SVN tagged copy:
129	ph10	122
130	ph10	212	svn copy svn://vcs.exim.org/pcre/code/trunk \
131			svn://vcs.exim.org/pcre/code/tags/pcre-7.x
132
133	ph10	122	Don't forget to update Freshmeat when the new release is out, and to tell
134			webmaster@pcre.org and the mailing list.
135
136
137			Future ideas (wish list)
138			------------------------
139
140			This section records a list of ideas so that they do not get forgotten. They
141	ph10	181	vary enormously in their usefulness and potential for implementation. Some are
142	ph10	122	very sensible; some are rather wacky. Some have been on this list for years;
143			others are relatively new.
144
145			. Optimization
146
147	ph10	181	There are always ideas for new optimizations so as to speed up pattern
148			matching. Most of them try to save work by recognizing a non-match without
149	ph10	122	having to scan all the possibilities. These are some that I've recorded:
150
151			* /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
152			slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
153	ph10	181	OTOH, this is pathological - the user could easily fix it.
154
155	ph10	122	* Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
156			to have little effect, and maybe makes things worse.
157	ph10	181
158			* "Ends with literal string" - note that a single character doesn't gain much
159	ph10	122	over the existing "required byte" (reqbyte) feature that just saves one
160			byte.
161	ph10	181
162	ph10	122	* These probably need to go in study():
163	ph10	181
164	ph10	122	o Remember an initial string rather than just 1 char?
165	ph10	181
166	ph10	122	o A required byte from alternatives - not just the last char, but an
167			earlier one if common to all alternatives.
168	ph10	181
169	ph10	122	o Minimum length of subject needed.
170	ph10	181
171	ph10	122	o Friedl contains other ideas.
172	ph10	181
173	ph10	122	. If Perl gets to a consistent state over the settings of capturing sub-
174			patterns inside repeats, see if we can match it. One example of the
175			difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
176			leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
177			because I think it needs much more state to be remembered.
178
179	ph10	181	. Perl 6 will be a revolution. Is it a revolution too far for PCRE?
180
181	ph10	122	. Unicode
182
183	ph10	181	* Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
184			character classes. For the moment, I've chosen not to support this for
185			backward compatibility, for speed, and because it would be messy to
186	ph10	122	implement.
187	ph10	181
188	ph10	122	* A different approach to Unicode might be to use a typedef to do everything
189			in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
190			new typedef to distinguish data from bits of compiled pattern that are in
191			bytes, I think. There would need to be conversion functions in and out. I
192			don't think this is particularly trivial - and anyway, Unicode now has
193			characters that need more than 16 bits, so is this at all sensible?
194	ph10	181
195	ph10	122	* There has been a request for direct support of 16-bit characters and
196			UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
197			is this worth it at all? One possible way of handling 16-bit characters
198			would be to "load" them in the same way that UTF-8 characters are loaded.
199	ph10	181
200	ph10	122	. Allow errorptr and erroroffset to be NULL. I don't like this idea.
201
202			. Line endings:
203
204			* Option to use NUL as a line terminator in subject strings. This could now
205			be done relatively easily since the extension to support LF, CR, and CRLF.
206	ph10	181	If this is done, a suitable option for pcregrep is also required.
207
208	ph10	122	. Option to provide the pattern with a length instead of with a NUL terminator.
209	ph10	181	This probably affects quite a few places in the code.
210	ph10	122
211	ph10	181	. Catch SIGSEGV for stack overflows?
212	ph10	122
213			. A feature to suspend a match via a callout was once requested.
214
215			. Option to convert results into character offsets and character lengths.
216
217	ph10	181	. Option for pcregrep to scan only the start of a file. I am not keen - this is
218	ph10	122	the job of "head".
219	ph10	181
220			. A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
221	ph10	122	preceded by a blank line, instead of adding it to every matched line, and (b)
222			support --outputfile=name.
223	ph10	181
224	ph10	122	. Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 7.
225
226	ph10	181	. Add a user pointer to pcre_malloc/free functions -- some option would be
227	ph10	122	needed to retain backward compatibility.
228	ph10	181
229	ph10	122	. Define a union for the results from pcre_fullinfo().
230
231	ph10	181	. Provide a "random access to the subject" facility so that the way in which it
232			is stored is independent of PCRE. For efficiency, it probably isn't possible
233	ph10	122	to switch this dynamically. It would have to be specified when PCRE was
234			compiled. PCRE would then call a function every time it wanted a character.
235	ph10	181
236	ph10	122	. Wild thought: the ability to compile from PCRE's internal byte code to a real
237			FSM and a very fast (third) matcher to process the result. There would be
238			even more restrictions than for pcre_dfa_exec(), however. This is not easy.
239	ph10	181
240	ph10	122	. Should pcretest have some private locale data, to avoid relying on the
241			available locales for the test data, since different OS have different ideas?
242			This won't be as thorough a test, but perhaps that doesn't really matter.
243	ph10	181
244			. pcregrep: add -rs for a sorted recurse? Having to store file names and sort
245	ph10	122	them will of course slow it down.
246
247	ph10	181	. Someone suggested --disable-callout to save code space when callouts are
248			never wanted. This seems rather marginal.
249	ph10	212
250			. Check names that consist entirely of digits: PCRE allows, but do Perl and
251			Python, etc?
252	ph10	122
253			Philip Hazel
254			Email local part: ph10
255			Email domain: cam.ac.uk
256	ph10	350	Last updated: 02 July 2008