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Tue Oct 11 10:29:36 2011 UTC (8 years, 2 months ago) by ph10
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Source tidies for 8.20-RC3.
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 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
45 README This file.
46
47 Unicode.tables The files in this directory, DerivedGeneralCategory.txt,
48 Scripts.txt and UnicodeData.txt, were downloaded from the
49 Unicode web site. They contain information about Unicode
50 characters and scripts.
51
52 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 the "maint" directory (see comments at its head).
56
57 ucptestdata A directory containing two files, testinput1 and testoutput1,
58 to use in conjunction with the ucptest program.
59
60 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
68
69 Updating to a new Unicode release
70 =================================
71
72 When there is a new release of Unicode, the files in Unicode.tables must be
73 refreshed from the web site. If the new version of Unicode adds new character
74 scripts, the source file ucp.h and both the MultiStage2.py and the
75 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
79 If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
80 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 in which they were introduced:
84
85 http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts
86
87 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 of test characters. The source file ucptest.c must be updated whenever new
90 Unicode script names are added.
91
92 Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
93 of Unicode script names.
94
95
96 Preparing for a PCRE release
97 ============================
98
99 This section contains a checklist of things that I consult before building a
100 distribution for a new release.
101
102 . Ensure that the version number and version date are correct in configure.ac.
103
104 . If new build options have been added, ensure that they are added to the CMake
105 files as well as to the autoconf files. The relevant files are CMakeLists.txt
106 and config-cmake.h.in. After making a release tarball, test it out with CMake
107 if there have been changes here.
108
109 . Run ./autogen.sh to ensure everything is up-to-date.
110
111 . Compile and test with many different config options, and combinations of
112 options. Also, test with valgrind by running "RunTest valgrind" and
113 "RunGrepTest valgrind" (which takes quite a long time). The script
114 maint/ManyConfigTests now encapsulates this testing. It runs tests with
115 different configurations, and it also runs some of them with valgrind, all of
116 which can take quite some time.
117
118 . Run perltest.pl on the test data for tests 1, 4, 6, 11, and 12. The output
119 should match the PCRE test output, apart from the version identification at
120 the start of each test. The other tests are not Perl-compatible (they use
121 various PCRE-specific features or options).
122
123 . It is possible to test with the emulated memmove() function by undefining
124 HAVE_MEMMOVE and HAVE_BCOPY in config.h, though I do not do this often. You
125 may see a number of "pcre_memmove defined but not used" warnings for the
126 modules in which there is no call to memmove(). These can be ignored.
127
128 . Documentation: check AUTHORS, COPYING, ChangeLog (check version and date),
129 INSTALL, LICENCE, NEWS (check version and date), NON-UNIX-USE, and README.
130 Many of these won't need changing, but over the long term things do change.
131
132 . I used to test new releases myself on a number of different operating
133 systems, using different compilers as well. For example, on Solaris it is
134 helpful to test using Sun's cc compiler as a change from gcc. Adding
135 -xarch=v9 to the cc options does a 64-bit test, but it also needs -S 64 for
136 pcretest to increase the stack size for test 2. Since I retired I can no
137 longer do this, but instead I rely on putting out release candidates for
138 folks on the pcre-dev list to test.
139
140
141 Making a PCRE release
142 =====================
143
144 Run PrepareRelease and commit the files that it changes (by removing trailing
145 spaces). The first thing this script does is to run CheckMan on the man pages;
146 if it finds any markup errors, it reports them and then aborts.
147
148 Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
149 and the zipball. Double-check with "svn status", then create an SVN tagged
150 copy:
151
152 svn copy svn://vcs.exim.org/pcre/code/trunk \
153 svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
154
155 Don't forget to update Freshmeat when the new release is out, and to tell
156 webmaster@pcre.org and the mailing list. Also, update the list of version
157 numbers in Bugzilla (edit products).
158
159
160 Future ideas (wish list)
161 ========================
162
163 This section records a list of ideas so that they do not get forgotten. They
164 vary enormously in their usefulness and potential for implementation. Some are
165 very sensible; some are rather wacky. Some have been on this list for years;
166 others are relatively new.
167
168 . Optimization
169
170 There are always ideas for new optimizations so as to speed up pattern
171 matching. Most of them try to save work by recognizing a non-match without
172 having to scan all the possibilities. These are some that I've recorded:
173
174 * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
175 slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
176 OTOH, this is pathological - the user could easily fix it.
177
178 * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
179 to have little effect, and maybe makes things worse.
180
181 * "Ends with literal string" - note that a single character doesn't gain much
182 over the existing "required byte" (reqbyte) feature that just remembers one
183 byte.
184
185 * These probably need to go in pcre_study():
186
187 o Remember an initial string rather than just 1 char?
188
189 o A required byte from alternatives - not just the last char, but an
190 earlier one if common to all alternatives.
191
192 o Friedl contains other ideas.
193
194 * pcre_study() does not set initial byte flags for Unicode property types
195 such as \p; I don't know how much benefit there would be for, for example,
196 setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
197 \p{N}.
198
199 * There is scope for more "auto-possessifying" in connection with \p and \P.
200
201 . If Perl gets to a consistent state over the settings of capturing sub-
202 patterns inside repeats, see if we can match it. One example of the
203 difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
204 leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
205 because I think it needs much more state to be remembered.
206
207 . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
208
209 . Unicode
210
211 * There has been a request for direct support of 16-bit characters and
212 UTF-16 (Bugzilla #1049). However, since Unicode is moving beyond purely
213 16-bit characters, is this worth it at all? One possible way of handling
214 16-bit characters would be to "load" them in the same way that UTF-8
215 characters are loaded. Another possibility is to provide a set of
216 translation functions, and build an index during translation so that the
217 returned offsets can automatically be translated (using the index) after a
218 match.
219
220 * A different approach to Unicode might be to use a typedef to do everything
221 in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
222 new typedef to distinguish data from bits of compiled pattern that are in
223 bytes, I think. There would need to be conversion functions in and out. I
224 don't think this is particularly trivial - and anyway, Unicode now has
225 characters that need more than 16 bits, so is this at all sensible? I
226 suspect not.
227
228 . Allow errorptr and erroroffset to be NULL. I don't like this idea.
229
230 . Line endings:
231
232 * Option to use NUL as a line terminator in subject strings. This could now
233 be done relatively easily since the extension to support LF, CR, and CRLF.
234 If it is done, a suitable option for pcregrep is also required.
235
236 . Option to provide the pattern with a length instead of with a NUL terminator.
237 This affects quite a few places in the code and is not trivial.
238
239 . Catch SIGSEGV for stack overflows?
240
241 . A feature to suspend a match via a callout was once requested.
242
243 . Option to convert results into character offsets and character lengths.
244
245 . Option for pcregrep to scan only the start of a file. I am not keen - this is
246 the job of "head".
247
248 . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
249 preceded by a blank line, instead of adding it to every matched line, and (b)
250 support --outputfile=name.
251
252 . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
253
254 . Add a user pointer to pcre_malloc/free functions -- some option would be
255 needed to retain backward compatibility.
256
257 . Define a union for the results from pcre_fullinfo().
258
259 . Provide a "random access to the subject" facility so that the way in which it
260 is stored is independent of PCRE. For efficiency, it probably isn't possible
261 to switch this dynamically. It would have to be specified when PCRE was
262 compiled. PCRE would then call a function every time it wanted a character.
263
264 . Wild thought: the ability to compile from PCRE's internal byte code to a real
265 FSM and a very fast (third) matcher to process the result. There would be
266 even more restrictions than for pcre_dfa_exec(), however. This is not easy.
267
268 . Should pcretest have some private locale data, to avoid relying on the
269 available locales for the test data, since different OS have different ideas?
270 This won't be as thorough a test, but perhaps that doesn't really matter.
271
272 . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
273 them will of course slow it down.
274
275 . Someone suggested --disable-callout to save code space when callouts are
276 never wanted. This seems rather marginal.
277
278 . Check names that consist entirely of digits: PCRE allows, but do Perl and
279 Python, etc?
280
281 . A user suggested a parameter to limit the length of string matched, for
282 example if the parameter is N, the current match should fail if the matched
283 substring exceeds N. This could apply to both match functions. The value
284 could be a new field in the extra block.
285
286 . Callouts with arguments: (?Cn:ARG) for instance.
287
288 . A user is going to supply a patch to generalize the API for user-specific
289 memory allocation so that it is more flexible in threaded environments. This
290 was promised a long time ago, and never appeared...
291
292 . Write a function that generates random matching strings for a compiled regex.
293
294 . Write a wrapper to maintain a structure with specified runtime parameters,
295 such as recurse limit, and pass these to PCRE each time it is called. Also
296 maybe malloc and free. A user sent a prototype.
297
298 . Pcregrep: an option to specify the output line separator, either as a string
299 or select from a fixed list. This is not dead easy, because at the moment it
300 outputs whatever is in the input file.
301
302 . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
303 non-thread-safe patch showed that this can help performance for patterns
304 where there are many alternatives. However, a simple thread-safe
305 implementation that I tried made things worse in many simple cases, so this
306 is not an obviously good thing.
307
308 . Make the longest lookbehind available via pcre_fullinfo(). This is not
309 straightforward because lookbehinds can be nested inside lookbehinds. This
310 case will have to be identified, and the amounts added. This should then give
311 the maximum possible lookbehind length. The reason for wanting this is to
312 help when implementing multi-segment matching using pcre_exec() with partial
313 matching and overlapping segments.
314
315 . PCRE cannot at present distinguish between subpatterns with different names,
316 but the same number (created by the use of ?|). In order to do so, a way of
317 remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
318 Now that (*MARK) has been implemented, it can perhaps be used as a way round
319 this problem.
320
321 . Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
322 "something" and the the #ifdef appears only in one place, in "something".
323
324 Philip Hazel
325 Email local part: ph10
326 Email domain: cam.ac.uk
327 Last updated: 11 October 2011

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