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Allow fixed-length subroutine calls in lookbehinds.
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 ----------------- This file is now OBSOLETE and no longer used ----------------
20 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 ----------------- This file is now OBSOLETE and no longer used ----------------
25
26 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 ManyConfigTests A shell script that runs "configure, make, test" a number of
31 times with different configuration settings.
32
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
39 README This file.
40
41 Unicode.tables The files in this directory, DerivedGeneralCategory.txt,
42 Scripts.txt and UnicodeData.txt, were downloaded from the
43 Unicode web site. They contain information about Unicode
44 characters and scripts.
45
46 ucptest.c A short C program for testing the Unicode property macros
47 that do lookups in the pcre_ucd.c data, mainly useful after
48 rebuilding the Unicode property table. Compile and run this in
49 the "maint" directory (see comments at its head).
50
51 ucptestdata A directory containing two files, testinput1 and testoutput1,
52 to use in conjunction with the ucptest program.
53
54 utf8.c A short, freestanding C program for converting a Unicode code
55 point into a sequence of bytes in the UTF-8 encoding, and vice
56 versa. If its argument is a hex number such as 0x1234, it
57 outputs a list of the equivalent UTF-8 bytes. If its argument
58 is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
59 treats them as a UTF-8 character and outputs the equivalent
60 code point in hex.
61
62
63 Updating to a new Unicode release
64 ---------------------------------
65
66 When there is a new release of Unicode, the files in Unicode.tables must be
67 refreshed from the web site. If the new version of Unicode adds new character
68 scripts, the source file ucp.h and both the MultiStage2.py and the
69 GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
70 can be run to generate a new version of pcre_ucd.c, and GenerateUtt.py can be
71 run to generate the tricky tables for inclusion in pcre_tables.c.
72
73 The ucptest program can be compiled and used to check that the new tables in
74 pcre_ucd.c work properly, using the data files in ucptestdata to check a number
75 of test characters.
76
77
78 Preparing for a PCRE release
79 ----------------------------
80
81 This section contains a checklist of things that I consult before building a
82 distribution for a new release.
83
84 . Ensure that the version number and version date are correct in configure.ac.
85
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
89 . Run ./autogen.sh to ensure everything is up-to-date.
90
91 . Compile and test with many different config options, and combinations of
92 options. The maint/ManyConfigTests script now encapsulates this testing.
93
94 . Run perltest.pl on the test data for tests 1, 4, 6, and 11. The first two can
95 be run with Perl 5.8 or 5.10; the last two require Perl 5.10. The output
96 should match the PCRE test output, apart from the version identification at
97 the start of each test. The other tests are not Perl-compatible (they use
98 various PCRE-specific features or options).
99
100 . Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
101 valgrind", though that takes quite a long time.
102
103 . It may also useful to test with Electric Fence, though the fact that it
104 grumbles for missing free() calls can be a nuisance. (A missing free() in
105 pcretest is hardly a big problem.) To build with EF, use:
106
107 LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
108
109 Then all normal runs use it to check for buffer overflow. Also run everything
110 with:
111
112 EF_PROTECT_BELOW=1 <whatever>
113
114 because there have been problems with lookbehinds that looked too far.
115
116 . Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
117 HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
118 used" warnings for the modules in which there is no call to memmove(). These
119 can be ignored.
120
121 . Documentation: check AUTHORS, COPYING, ChangeLog (check version and date),
122 INSTALL, LICENCE, NEWS (check version and date), NON-UNIX-USE, and README.
123 Many of these won't need changing, but over the long term things do change.
124
125 . Man pages: Check all man pages for \ not followed by e or f or " because
126 that indicates a markup error.
127
128 . When the release is built, test it on a number of different operating
129 systems if possible, and using different compilers as well. For example,
130 on Solaris it is helpful to test using Sun's cc compiler as a change from
131 gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
132 needs -S 64 for pcretest to increase the stack size for test 2.
133
134
135 Making a PCRE release
136 ---------------------
137
138 Run PrepareRelease and commit the files that it changes (by removing trailing
139 spaces). Then run "make distcheck" to create the tarballs and the zipball.
140 Double-check with "svn status", then create an SVN tagged copy:
141
142 svn copy svn://vcs.exim.org/pcre/code/trunk \
143 svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
144
145 Don't forget to update Freshmeat when the new release is out, and to tell
146 webmaster@pcre.org and the mailing list.
147
148
149 Future ideas (wish list)
150 ------------------------
151
152 This section records a list of ideas so that they do not get forgotten. They
153 vary enormously in their usefulness and potential for implementation. Some are
154 very sensible; some are rather wacky. Some have been on this list for years;
155 others are relatively new.
156
157 . Optimization
158
159 There are always ideas for new optimizations so as to speed up pattern
160 matching. Most of them try to save work by recognizing a non-match without
161 having to scan all the possibilities. These are some that I've recorded:
162
163 * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
164 slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
165 OTOH, this is pathological - the user could easily fix it.
166
167 * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
168 to have little effect, and maybe makes things worse.
169
170 * "Ends with literal string" - note that a single character doesn't gain much
171 over the existing "required byte" (reqbyte) feature that just remembers one
172 byte.
173
174 * These probably need to go in study():
175
176 o Remember an initial string rather than just 1 char?
177
178 o A required byte from alternatives - not just the last char, but an
179 earlier one if common to all alternatives.
180
181 o Minimum length of subject needed (see also next . bullet).
182
183 o Friedl contains other ideas.
184
185 . There was a request for a way of finding the minimum subject length that can
186 match a given pattern. (If this were available, it could be usefully added
187 to study() - see above.) This is easy for simple cases, but I haven't figured
188 out how to handle recursion.
189
190 . If Perl gets to a consistent state over the settings of capturing sub-
191 patterns inside repeats, see if we can match it. One example of the
192 difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
193 leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
194 because I think it needs much more state to be remembered.
195
196 . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
197
198 . Unicode
199
200 * Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
201 character classes. For the moment, I've chosen not to support this for
202 backward compatibility, for speed, and because it would be messy to
203 implement.
204
205 * A different approach to Unicode might be to use a typedef to do everything
206 in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
207 new typedef to distinguish data from bits of compiled pattern that are in
208 bytes, I think. There would need to be conversion functions in and out. I
209 don't think this is particularly trivial - and anyway, Unicode now has
210 characters that need more than 16 bits, so is this at all sensible?
211
212 * There has been a request for direct support of 16-bit characters and
213 UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
214 is this worth it at all? One possible way of handling 16-bit characters
215 would be to "load" them in the same way that UTF-8 characters are loaded.
216
217 . Allow errorptr and erroroffset to be NULL. I don't like this idea.
218
219 . Line endings:
220
221 * Option to use NUL as a line terminator in subject strings. This could now
222 be done relatively easily since the extension to support LF, CR, and CRLF.
223 If it is done, a suitable option for pcregrep is also required.
224
225 . Option to provide the pattern with a length instead of with a NUL terminator.
226 This affects quite a few places in the code and is not trivial.
227
228 . Catch SIGSEGV for stack overflows?
229
230 . A feature to suspend a match via a callout was once requested.
231
232 . Option to convert results into character offsets and character lengths.
233
234 . Option for pcregrep to scan only the start of a file. I am not keen - this is
235 the job of "head".
236
237 . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
238 preceded by a blank line, instead of adding it to every matched line, and (b)
239 support --outputfile=name.
240
241 . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
242
243 . Add a user pointer to pcre_malloc/free functions -- some option would be
244 needed to retain backward compatibility.
245
246 . Define a union for the results from pcre_fullinfo().
247
248 . Provide a "random access to the subject" facility so that the way in which it
249 is stored is independent of PCRE. For efficiency, it probably isn't possible
250 to switch this dynamically. It would have to be specified when PCRE was
251 compiled. PCRE would then call a function every time it wanted a character.
252
253 . Wild thought: the ability to compile from PCRE's internal byte code to a real
254 FSM and a very fast (third) matcher to process the result. There would be
255 even more restrictions than for pcre_dfa_exec(), however. This is not easy.
256
257 . Should pcretest have some private locale data, to avoid relying on the
258 available locales for the test data, since different OS have different ideas?
259 This won't be as thorough a test, but perhaps that doesn't really matter.
260
261 . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
262 them will of course slow it down.
263
264 . Someone suggested --disable-callout to save code space when callouts are
265 never wanted. This seems rather marginal.
266
267 . Check names that consist entirely of digits: PCRE allows, but do Perl and
268 Python, etc?
269
270 . A user suggested a parameter to limit the length of string matched, for
271 example if the parameter is N, the current match should fail if the matched
272 substring exceeds N. This could apply to both match functions. The value
273 could be a new field in the extra block.
274
275 . Callouts with arguments: (?Cn:ARG) for instance.
276
277 . A user is going to supply a patch to generalize the API for user-specific
278 memory allocation so that it is more flexible in threaded environments. Thiw
279 was promised a long time ago, and never appeared...
280
281 . Write a function that generates random matching strings for a compiled regex.
282
283 . Write a wrapper to maintain a structure with specified runtime parameters,
284 such as recurse limit, and pass these to PCRE each time it is called. Also
285 maybe malloc and free. A user sent a prototype.
286
287 . Pcregrep: an option to specify the output line separator, either as a string
288 or select from a fixed list. This is not dead easy, because at the moment it
289 outputs whatever is in the input file.
290
291 . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
292 non-thread-safe patch showed that this can help performance for patterns
293 where there are many alternatives. However, a simple thread-safe
294 implementation that I tried made things worse in many simple cases, so this
295 is not an obviously good thing.
296
297 . Make the longest lookbehind available via pcre_fullinfo(). This is not
298 straightforward because lookbehinds can be nested inside lookbehinds. This
299 case will have to be identified, and the amounts added. This should then give
300 the maximum possible lookbehind length. The reason for wanting this is to
301 help when implementing multi-segment matching using pcre_exec() with partial
302 matching and overlapping segments.
303
304 . PCRE cannot at present distinguish between subpatterns with different names,
305 but the same number (created by the use of ?|). In order to do so, a way of
306 remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
307
308 Philip Hazel
309 Email local part: ph10
310 Email domain: cam.ac.uk
311 Last updated: 20 September 2009

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