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Tidies of documenation and code while preparing for release.
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.
106
107 . Run ./autogen.sh to ensure everything is up-to-date.
108
109 . Compile and test with many different config options, and combinations of
110 options. The maint/ManyConfigTests script now encapsulates this testing.
111
112 . Run perltest.pl on the test data for tests 1, 4, 6, and 11. The output should
113 match the PCRE test output, apart from the version identification at the
114 start of each test. The other tests are not Perl-compatible (they use various
115 PCRE-specific features or options).
116
117 . Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
118 valgrind", though that takes quite a long time.
119
120 . Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
121 HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
122 used" warnings for the modules in which there is no call to memmove(). These
123 can be ignored.
124
125 . Documentation: check AUTHORS, COPYING, ChangeLog (check version and date),
126 INSTALL, LICENCE, NEWS (check version and date), NON-UNIX-USE, and README.
127 Many of these won't need changing, but over the long term things do change.
128
129 . Man pages: Check all man pages for \ not followed by e or f or " because
130 that indicates a markup error. However, there is one exception: pcredemo.3,
131 which is created from the pcredemo.c program. It contains three instances
132 of \\n.
133
134 . When the release is built, test it on a number of different operating
135 systems if possible, and using different compilers as well. For example,
136 on Solaris it is helpful to test using Sun's cc compiler as a change from
137 gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
138 needs -S 64 for pcretest to increase the stack size for test 2.
139
140
141 Making a PCRE release
142 =====================
143
144 Run PrepareRelease and commit the files that it changes (by removing trailing
145 spaces). Then run "make distcheck" to create the tarballs and the zipball.
146 Double-check with "svn status", then create an SVN tagged copy:
147
148 svn copy svn://vcs.exim.org/pcre/code/trunk \
149 svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
150
151 Don't forget to update Freshmeat when the new release is out, and to tell
152 webmaster@pcre.org and the mailing list. Also, update the list of version
153 numbers in Bugzilla (edit products).
154
155
156 Future ideas (wish list)
157 ========================
158
159 This section records a list of ideas so that they do not get forgotten. They
160 vary enormously in their usefulness and potential for implementation. Some are
161 very sensible; some are rather wacky. Some have been on this list for years;
162 others are relatively new.
163
164 . Optimization
165
166 There are always ideas for new optimizations so as to speed up pattern
167 matching. Most of them try to save work by recognizing a non-match without
168 having to scan all the possibilities. These are some that I've recorded:
169
170 * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
171 slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
172 OTOH, this is pathological - the user could easily fix it.
173
174 * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
175 to have little effect, and maybe makes things worse.
176
177 * "Ends with literal string" - note that a single character doesn't gain much
178 over the existing "required byte" (reqbyte) feature that just remembers one
179 byte.
180
181 * These probably need to go in pcre_study():
182
183 o Remember an initial string rather than just 1 char?
184
185 o A required byte from alternatives - not just the last char, but an
186 earlier one if common to all alternatives.
187
188 o Friedl contains other ideas.
189
190 * pcre_study() does not set initial byte flags for Unicode property types
191 such as \p; I don't know how much benefit there would be for, for example,
192 setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
193 \p{N}.
194
195 * There is scope for more "auto-possessifying" in connection with \p and \P.
196
197 . If Perl gets to a consistent state over the settings of capturing sub-
198 patterns inside repeats, see if we can match it. One example of the
199 difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
200 leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
201 because I think it needs much more state to be remembered.
202
203 . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
204
205 . Unicode
206
207 * A different approach to Unicode might be to use a typedef to do everything
208 in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
209 new typedef to distinguish data from bits of compiled pattern that are in
210 bytes, I think. There would need to be conversion functions in and out. I
211 don't think this is particularly trivial - and anyway, Unicode now has
212 characters that need more than 16 bits, so is this at all sensible?
213
214 * There has been a request for direct support of 16-bit characters and
215 UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
216 is this worth it at all? One possible way of handling 16-bit characters
217 would be to "load" them in the same way that UTF-8 characters are loaded.
218
219 . Allow errorptr and erroroffset to be NULL. I don't like this idea.
220
221 . Line endings:
222
223 * Option to use NUL as a line terminator in subject strings. This could now
224 be done relatively easily since the extension to support LF, CR, and CRLF.
225 If it is done, a suitable option for pcregrep is also required.
226
227 . Option to provide the pattern with a length instead of with a NUL terminator.
228 This affects quite a few places in the code and is not trivial.
229
230 . Catch SIGSEGV for stack overflows?
231
232 . A feature to suspend a match via a callout was once requested.
233
234 . Option to convert results into character offsets and character lengths.
235
236 . Option for pcregrep to scan only the start of a file. I am not keen - this is
237 the job of "head".
238
239 . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
240 preceded by a blank line, instead of adding it to every matched line, and (b)
241 support --outputfile=name.
242
243 . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
244
245 . Add a user pointer to pcre_malloc/free functions -- some option would be
246 needed to retain backward compatibility.
247
248 . Define a union for the results from pcre_fullinfo().
249
250 . Provide a "random access to the subject" facility so that the way in which it
251 is stored is independent of PCRE. For efficiency, it probably isn't possible
252 to switch this dynamically. It would have to be specified when PCRE was
253 compiled. PCRE would then call a function every time it wanted a character.
254
255 . Wild thought: the ability to compile from PCRE's internal byte code to a real
256 FSM and a very fast (third) matcher to process the result. There would be
257 even more restrictions than for pcre_dfa_exec(), however. This is not easy.
258
259 . Should pcretest have some private locale data, to avoid relying on the
260 available locales for the test data, since different OS have different ideas?
261 This won't be as thorough a test, but perhaps that doesn't really matter.
262
263 . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
264 them will of course slow it down.
265
266 . Someone suggested --disable-callout to save code space when callouts are
267 never wanted. This seems rather marginal.
268
269 . Check names that consist entirely of digits: PCRE allows, but do Perl and
270 Python, etc?
271
272 . A user suggested a parameter to limit the length of string matched, for
273 example if the parameter is N, the current match should fail if the matched
274 substring exceeds N. This could apply to both match functions. The value
275 could be a new field in the extra block.
276
277 . Callouts with arguments: (?Cn:ARG) for instance.
278
279 . A user is going to supply a patch to generalize the API for user-specific
280 memory allocation so that it is more flexible in threaded environments. This
281 was promised a long time ago, and never appeared...
282
283 . Write a function that generates random matching strings for a compiled regex.
284
285 . Write a wrapper to maintain a structure with specified runtime parameters,
286 such as recurse limit, and pass these to PCRE each time it is called. Also
287 maybe malloc and free. A user sent a prototype.
288
289 . Pcregrep: an option to specify the output line separator, either as a string
290 or select from a fixed list. This is not dead easy, because at the moment it
291 outputs whatever is in the input file.
292
293 . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
294 non-thread-safe patch showed that this can help performance for patterns
295 where there are many alternatives. However, a simple thread-safe
296 implementation that I tried made things worse in many simple cases, so this
297 is not an obviously good thing.
298
299 . Make the longest lookbehind available via pcre_fullinfo(). This is not
300 straightforward because lookbehinds can be nested inside lookbehinds. This
301 case will have to be identified, and the amounts added. This should then give
302 the maximum possible lookbehind length. The reason for wanting this is to
303 help when implementing multi-segment matching using pcre_exec() with partial
304 matching and overlapping segments.
305
306 . PCRE cannot at present distinguish between subpatterns with different names,
307 but the same number (created by the use of ?|). In order to do so, a way of
308 remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
309 Now that (*MARK) has been implemented, it can perhaps be used as a way round
310 this problem.
311
312 . Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
313 "something" and the the #ifdef appears only in one place, in "something".
314
315 Philip Hazel
316 Email local part: ph10
317 Email domain: cam.ac.uk
318 Last updated: 24 November 2010

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