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.  

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 the
MultiStage2.py script can then be run to generate a new version of pcre_ucd.c
and the GenerateUtt.py can be run to generate the tricky tables for inclusion
in pcre_tables.c.

The ucptest program can then 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.


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: 04 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	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			offsets, which is tedious to maintain by hand.
29
30	ph10	129	ManyConfigTests A shell script that runs "configure, make, test" a number of
31			times with different configuration settings.
32	ph10	350
33			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			Unicode web site. Run this script in the "maint" directory.
36			The generated file contains the tables for a 2-stage lookup
37			of Unicode properties.
38	ph10	181
39	ph10	350	Unicode.tables The files in this directory, DerivedGeneralCategory.txt,
40			Scripts.txt and UnicodeData.txt, were downloaded from the
41			Unicode web site. They contain information about Unicode
42			characters and scripts.
43	ph10	181
44	ph10	350	ucptest.c A short C program for testing the Unicode property macros
45			that do lookups in the pcre_ucd.c data, mainly useful after
46			rebuilding the Unicode property table. Compile and run this in
47	ph10	351	the "maint" directory (see comments at its head).
48	ph10	181
49	ph10	129	ucptestdata A directory containing two files, testinput1 and testoutput1,
50			to use in conjunction with the ucptest program.
51	ph10	181
52	ph10	129	utf8.c A short, freestanding C program for converting a Unicode code
53			point into a sequence of bytes in the UTF-8 encoding, and vice
54			versa. If its argument is a hex number such as 0x1234, it
55			outputs a list of the equivalent UTF-8 bytes. If its argument
56			is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
57			treats them as a UTF-8 character and outputs the equivalent
58			code point in hex.
59	ph10	97
60	ph10	181
61	ph10	122	Updating to a new Unicode release
62			---------------------------------
63
64	ph10	181	When there is a new release of Unicode, the files in Unicode.tables must be
65	ph10	351	refreshed from the web site. If the new version of Unicode adds new character
66	ph10	352	scripts, the source file ucp.h and both the MultiStage2.py and the
67			GenerateUtt.py scripts must be edited to add the new names. Then the
68			MultiStage2.py script can then be run to generate a new version of pcre_ucd.c
69			and the GenerateUtt.py can be run to generate the tricky tables for inclusion
70			in pcre_tables.c.
71	ph10	122
72	ph10	351	The ucptest program can then be compiled and used to check that the new tables
73			in pcre_ucd.c work properly, using the data files in ucptestdata to check a
74			number of test characters.
75	ph10	122
76	ph10	351
77	ph10	122	Preparing for a PCRE release
78			----------------------------
79
80			This section contains a checklist of things that I consult before building a
81			distribution for a new release.
82
83	ph10	155	. Ensure that the version number and version date are correct in configure.ac,
84			ChangeLog, and NEWS.
85	ph10	292
86			. If new build options have been added, ensure that they are added to the CMake
87			files as well as to the autoconf files.
88	ph10	122
89			. Run ./autogen.sh to ensure everything is up-to-date.
90
91	ph10	181	. Compile and test with many different config options, and combinations of
92	ph10	129	options. The maint/ManyConfigTests script now encapsulates this testing.
93	ph10	181
94	ph10	122	. Run perltest.pl on the test data for tests 1 and 4. The output should match
95	ph10	181	the PCRE test output, apart from the version identification at the top. The
96	ph10	122	other tests are not Perl-compatible (they use various special PCRE options).
97
98			. Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
99			valgrind", though that takes quite a long time.
100	ph10	181
101			. It may also useful to test with Electric Fence, though the fact that it
102			grumbles for missing free() calls can be a nuisance. (A missing free() in
103	ph10	122	pcretest is hardly a big problem.) To build with EF, use:
104	ph10	181
105	ph10	122	LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
106
107			Then all normal runs use it to check for buffer overflow. Also run everything
108			with:
109	ph10	181
110			EF_PROTECT_BELOW=1 <whatever>
111
112			because there have been problems with lookbehinds that looked too far.
113
114			. Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
115			HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
116	ph10	155	used" warnings for the modules in which there is no call to memmove(). These
117			can be ignored.
118	ph10	122
119	ph10	181	. Documentation: check AUTHORS, COPYING, ChangeLog (check date), INSTALL,
120			LICENCE, NEWS (check date), NON-UNIX-USE, and README. Many of these won't
121	ph10	122	need changing, but over the long term things do change.
122	ph10	181
123	ph10	122	. Man pages: Check all man pages for \ not followed by e or f or " because
124			that indicates a markup error.
125
126	ph10	181	. When the release is built, test it on a number of different operating
127	ph10	155	systems if possible, and using different compilers as well. For example,
128			on Solaris it is helpful to test using Sun's cc compiler as a change from
129			gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
130			needs -S 64 for pcretest to increase the stack size for test 2.
131	ph10	122
132	ph10	155
133	ph10	122	Making a PCRE release
134			---------------------
135
136			Run PrepareRelease and commit the files that it changes (by removing trailing
137	ph10	155	spaces). Then run "make distcheck" to create the tarballs and the zipball.
138	ph10	212	Double-check with "svn status", then create an SVN tagged copy:
139	ph10	122
140	ph10	212	svn copy svn://vcs.exim.org/pcre/code/trunk \
141			svn://vcs.exim.org/pcre/code/tags/pcre-7.x
142
143	ph10	122	Don't forget to update Freshmeat when the new release is out, and to tell
144			webmaster@pcre.org and the mailing list.
145
146
147			Future ideas (wish list)
148			------------------------
149
150			This section records a list of ideas so that they do not get forgotten. They
151	ph10	181	vary enormously in their usefulness and potential for implementation. Some are
152	ph10	122	very sensible; some are rather wacky. Some have been on this list for years;
153			others are relatively new.
154
155			. Optimization
156
157	ph10	181	There are always ideas for new optimizations so as to speed up pattern
158			matching. Most of them try to save work by recognizing a non-match without
159	ph10	122	having to scan all the possibilities. These are some that I've recorded:
160
161			* /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
162			slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
163	ph10	181	OTOH, this is pathological - the user could easily fix it.
164
165	ph10	122	* Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
166			to have little effect, and maybe makes things worse.
167	ph10	181
168			* "Ends with literal string" - note that a single character doesn't gain much
169	ph10	122	over the existing "required byte" (reqbyte) feature that just saves one
170			byte.
171	ph10	181
172	ph10	122	* These probably need to go in study():
173	ph10	181
174	ph10	122	o Remember an initial string rather than just 1 char?
175	ph10	181
176	ph10	122	o A required byte from alternatives - not just the last char, but an
177			earlier one if common to all alternatives.
178	ph10	181
179	ph10	122	o Minimum length of subject needed.
180	ph10	181
181	ph10	122	o Friedl contains other ideas.
182	ph10	181
183	ph10	122	. If Perl gets to a consistent state over the settings of capturing sub-
184			patterns inside repeats, see if we can match it. One example of the
185			difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
186			leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
187			because I think it needs much more state to be remembered.
188
189	ph10	181	. Perl 6 will be a revolution. Is it a revolution too far for PCRE?
190
191	ph10	122	. Unicode
192
193	ph10	181	* Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
194			character classes. For the moment, I've chosen not to support this for
195			backward compatibility, for speed, and because it would be messy to
196	ph10	122	implement.
197	ph10	181
198	ph10	122	* A different approach to Unicode might be to use a typedef to do everything
199			in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
200			new typedef to distinguish data from bits of compiled pattern that are in
201			bytes, I think. There would need to be conversion functions in and out. I
202			don't think this is particularly trivial - and anyway, Unicode now has
203			characters that need more than 16 bits, so is this at all sensible?
204	ph10	181
205	ph10	122	* There has been a request for direct support of 16-bit characters and
206			UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
207			is this worth it at all? One possible way of handling 16-bit characters
208			would be to "load" them in the same way that UTF-8 characters are loaded.
209	ph10	181
210	ph10	122	. Allow errorptr and erroroffset to be NULL. I don't like this idea.
211
212			. Line endings:
213
214			* Option to use NUL as a line terminator in subject strings. This could now
215			be done relatively easily since the extension to support LF, CR, and CRLF.
216	ph10	181	If this is done, a suitable option for pcregrep is also required.
217
218	ph10	122	. Option to provide the pattern with a length instead of with a NUL terminator.
219	ph10	181	This probably affects quite a few places in the code.
220	ph10	122
221	ph10	181	. Catch SIGSEGV for stack overflows?
222	ph10	122
223			. A feature to suspend a match via a callout was once requested.
224
225			. Option to convert results into character offsets and character lengths.
226
227	ph10	181	. Option for pcregrep to scan only the start of a file. I am not keen - this is
228	ph10	122	the job of "head".
229	ph10	181
230			. A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
231	ph10	122	preceded by a blank line, instead of adding it to every matched line, and (b)
232			support --outputfile=name.
233	ph10	181
234	ph10	122	. Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 7.
235
236	ph10	181	. Add a user pointer to pcre_malloc/free functions -- some option would be
237	ph10	122	needed to retain backward compatibility.
238	ph10	181
239	ph10	122	. Define a union for the results from pcre_fullinfo().
240
241	ph10	181	. Provide a "random access to the subject" facility so that the way in which it
242			is stored is independent of PCRE. For efficiency, it probably isn't possible
243	ph10	122	to switch this dynamically. It would have to be specified when PCRE was
244			compiled. PCRE would then call a function every time it wanted a character.
245	ph10	181
246	ph10	122	. Wild thought: the ability to compile from PCRE's internal byte code to a real
247			FSM and a very fast (third) matcher to process the result. There would be
248			even more restrictions than for pcre_dfa_exec(), however. This is not easy.
249	ph10	181
250	ph10	122	. Should pcretest have some private locale data, to avoid relying on the
251			available locales for the test data, since different OS have different ideas?
252			This won't be as thorough a test, but perhaps that doesn't really matter.
253	ph10	181
254			. pcregrep: add -rs for a sorted recurse? Having to store file names and sort
255	ph10	122	them will of course slow it down.
256
257	ph10	181	. Someone suggested --disable-callout to save code space when callouts are
258			never wanted. This seems rather marginal.
259	ph10	212
260			. Check names that consist entirely of digits: PCRE allows, but do Perl and
261			Python, etc?
262	ph10	122
263			Philip Hazel
264			Email local part: ph10
265			Email domain: cam.ac.uk
266	ph10	351	Last updated: 04 July 2008