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

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.

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

Unicode.tables   The files in this directory, 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 functions
                 in pcre_ucp_searchfuncs.c, 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 Buildupctable script can then be run to
generate a new version of ucptable.h. 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: 27 December 2007
1	MAINTENANCE README FOR PCRE
2	---------------------------
3
4	The files in the "maint" directory of the PCRE source contain data, scripts,
5	and programs that are used for the maintenance of PCRE, but which do not form
6	part of the PCRE distribution tarballs. This document describes these files and
7	also contains some notes for maintainers. Its contents are:
8
9	Files in the maint directory
10	Updating to a new Unicode release
11	Preparing for a PCRE release
12	Making a PCRE release
13	Long-term ideas (wish list)
14
15
16	Files in the maint directory
17	----------------------------
18
19	Builducptable A Perl script that creates the contents of the ucptable.h file
20	from two Unicode data files, which themselves are downloaded
21	from the Unicode web site. Run this script in the "maint"
22	directory.
23
24	ManyConfigTests A shell script that runs "configure, make, test" a number of
25	times with different configuration settings.
26
27	Unicode.tables The files in this directory, Scripts.txt and UnicodeData.txt,
28	were downloaded from the Unicode web site. They contain
29	information about Unicode characters and scripts.
30
31	ucptest.c A short C program for testing the Unicode property functions
32	in pcre_ucp_searchfuncs.c, mainly useful after rebuilding the
33	Unicode property table. Compile and run this in the "maint"
34	directory.
35
36	ucptestdata A directory containing two files, testinput1 and testoutput1,
37	to use in conjunction with the ucptest program.
38
39	utf8.c A short, freestanding C program for converting a Unicode code
40	point into a sequence of bytes in the UTF-8 encoding, and vice
41	versa. If its argument is a hex number such as 0x1234, it
42	outputs a list of the equivalent UTF-8 bytes. If its argument
43	is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
44	treats them as a UTF-8 character and outputs the equivalent
45	code point in hex.
46
47
48	Updating to a new Unicode release
49	---------------------------------
50
51	When there is a new release of Unicode, the files in Unicode.tables must be
52	refreshed from the web site, and the Buildupctable script can then be run to
53	generate a new version of ucptable.h. The ucptest program can be used to check
54	that the resulting table works properly, using the data files in ucptestdata to
55	check a number of test characters.
56
57
58	Preparing for a PCRE release
59	----------------------------
60
61	This section contains a checklist of things that I consult before building a
62	distribution for a new release.
63
64	. Ensure that the version number and version date are correct in configure.ac,
65	ChangeLog, and NEWS.
66
67	. If new build options have been added, ensure that they are added to the CMake
68	files as well as to the autoconf files.
69
70	. Run ./autogen.sh to ensure everything is up-to-date.
71
72	. Compile and test with many different config options, and combinations of
73	options. The maint/ManyConfigTests script now encapsulates this testing.
74
75	. Run perltest.pl on the test data for tests 1 and 4. The output should match
76	the PCRE test output, apart from the version identification at the top. The
77	other tests are not Perl-compatible (they use various special PCRE options).
78
79	. Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
80	valgrind", though that takes quite a long time.
81
82	. It may also useful to test with Electric Fence, though the fact that it
83	grumbles for missing free() calls can be a nuisance. (A missing free() in
84	pcretest is hardly a big problem.) To build with EF, use:
85
86	LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
87
88	Then all normal runs use it to check for buffer overflow. Also run everything
89	with:
90
91	EF_PROTECT_BELOW=1 <whatever>
92
93	because there have been problems with lookbehinds that looked too far.
94
95	. Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
96	HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
97	used" warnings for the modules in which there is no call to memmove(). These
98	can be ignored.
99
100	. Documentation: check AUTHORS, COPYING, ChangeLog (check date), INSTALL,
101	LICENCE, NEWS (check date), NON-UNIX-USE, and README. Many of these won't
102	need changing, but over the long term things do change.
103
104	. Man pages: Check all man pages for \ not followed by e or f or " because
105	that indicates a markup error.
106
107	. When the release is built, test it on a number of different operating
108	systems if possible, and using different compilers as well. For example,
109	on Solaris it is helpful to test using Sun's cc compiler as a change from
110	gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
111	needs -S 64 for pcretest to increase the stack size for test 2.
112
113
114	Making a PCRE release
115	---------------------
116
117	Run PrepareRelease and commit the files that it changes (by removing trailing
118	spaces). Then run "make distcheck" to create the tarballs and the zipball.
119	Double-check with "svn status", then create an SVN tagged copy:
120
121	svn copy svn://vcs.exim.org/pcre/code/trunk \
122	svn://vcs.exim.org/pcre/code/tags/pcre-7.x
123
124	Don't forget to update Freshmeat when the new release is out, and to tell
125	webmaster@pcre.org and the mailing list.
126
127
128	Future ideas (wish list)
129	------------------------
130
131	This section records a list of ideas so that they do not get forgotten. They
132	vary enormously in their usefulness and potential for implementation. Some are
133	very sensible; some are rather wacky. Some have been on this list for years;
134	others are relatively new.
135
136	. Optimization
137
138	There are always ideas for new optimizations so as to speed up pattern
139	matching. Most of them try to save work by recognizing a non-match without
140	having to scan all the possibilities. These are some that I've recorded:
141
142	* /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
143	slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
144	OTOH, this is pathological - the user could easily fix it.
145
146	* Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
147	to have little effect, and maybe makes things worse.
148
149	* "Ends with literal string" - note that a single character doesn't gain much
150	over the existing "required byte" (reqbyte) feature that just saves one
151	byte.
152
153	* These probably need to go in study():
154
155	o Remember an initial string rather than just 1 char?
156
157	o A required byte from alternatives - not just the last char, but an
158	earlier one if common to all alternatives.
159
160	o Minimum length of subject needed.
161
162	o Friedl contains other ideas.
163
164	. If Perl gets to a consistent state over the settings of capturing sub-
165	patterns inside repeats, see if we can match it. One example of the
166	difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
167	leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
168	because I think it needs much more state to be remembered.
169
170	. Perl 6 will be a revolution. Is it a revolution too far for PCRE?
171
172	. Unicode
173
174	* Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
175	character classes. For the moment, I've chosen not to support this for
176	backward compatibility, for speed, and because it would be messy to
177	implement.
178
179	* A different approach to Unicode might be to use a typedef to do everything
180	in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
181	new typedef to distinguish data from bits of compiled pattern that are in
182	bytes, I think. There would need to be conversion functions in and out. I
183	don't think this is particularly trivial - and anyway, Unicode now has
184	characters that need more than 16 bits, so is this at all sensible?
185
186	* There has been a request for direct support of 16-bit characters and
187	UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
188	is this worth it at all? One possible way of handling 16-bit characters
189	would be to "load" them in the same way that UTF-8 characters are loaded.
190
191	. Allow errorptr and erroroffset to be NULL. I don't like this idea.
192
193	. Line endings:
194
195	* Option to use NUL as a line terminator in subject strings. This could now
196	be done relatively easily since the extension to support LF, CR, and CRLF.
197	If this is done, a suitable option for pcregrep is also required.
198
199	. Option to provide the pattern with a length instead of with a NUL terminator.
200	This probably affects quite a few places in the code.
201
202	. Catch SIGSEGV for stack overflows?
203
204	. A feature to suspend a match via a callout was once requested.
205
206	. Option to convert results into character offsets and character lengths.
207
208	. Option for pcregrep to scan only the start of a file. I am not keen - this is
209	the job of "head".
210
211	. A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
212	preceded by a blank line, instead of adding it to every matched line, and (b)
213	support --outputfile=name.
214
215	. Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 7.
216
217	. Add a user pointer to pcre_malloc/free functions -- some option would be
218	needed to retain backward compatibility.
219
220	. Define a union for the results from pcre_fullinfo().
221
222	. Provide a "random access to the subject" facility so that the way in which it
223	is stored is independent of PCRE. For efficiency, it probably isn't possible
224	to switch this dynamically. It would have to be specified when PCRE was
225	compiled. PCRE would then call a function every time it wanted a character.
226
227	. Wild thought: the ability to compile from PCRE's internal byte code to a real
228	FSM and a very fast (third) matcher to process the result. There would be
229	even more restrictions than for pcre_dfa_exec(), however. This is not easy.
230
231	. Should pcretest have some private locale data, to avoid relying on the
232	available locales for the test data, since different OS have different ideas?
233	This won't be as thorough a test, but perhaps that doesn't really matter.
234
235	. pcregrep: add -rs for a sorted recurse? Having to store file names and sort
236	them will of course slow it down.
237
238	. Someone suggested --disable-callout to save code space when callouts are
239	never wanted. This seems rather marginal.
240
241	. Check names that consist entirely of digits: PCRE allows, but do Perl and
242	Python, etc?
243
244	Philip Hazel
245	Email local part: ph10
246	Email domain: cam.ac.uk
247	Last updated: 27 December 2007