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Tue Aug 2 11:00:40 2011 UTC (8 years ago) by ph10
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Documentation and general text tidies in preparation for test 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. 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. The maint/ManyConfigTests script now encapsulates this testing.
113
114 . Run perltest.pl on the test data for tests 1, 4, 6, 11, and 12. The output
115 should match the PCRE test output, apart from the version identification at
116 the start of each test. The other tests are not Perl-compatible (they use
117 various PCRE-specific features or options).
118
119 . Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
120 valgrind", though that takes quite a long time.
121
122 . It is possible to test with the emulated memmove() function by undefining
123 HAVE_MEMMOVE and HAVE_BCOPY in config.h, though I do not do this often. You
124 may see a number of "pcre_memmove defined but not used" warnings for the
125 modules in which there is no call to memmove(). These can be ignored.
126
127 . Documentation: check AUTHORS, COPYING, ChangeLog (check version and date),
128 INSTALL, LICENCE, NEWS (check version and date), NON-UNIX-USE, and README.
129 Many of these won't need changing, but over the long term things do change.
130
131 . I used to test new releases myself on a number of different operating
132 systems, using different compilers as well. For example, on Solaris it is
133 helpful to test using Sun's cc compiler as a change from gcc. Adding
134 -xarch=v9 to the cc options does a 64-bit test, but it also needs -S 64 for
135 pcretest to increase the stack size for test 2. Since I retired I can no
136 longer do this, but instead I rely on putting out release candidates for
137 folks on the pcre-dev list to test.
138
139
140 Making a PCRE release
141 =====================
142
143 Run PrepareRelease and commit the files that it changes (by removing trailing
144 spaces). The first thing this script does is to run CheckMan on the man pages;
145 if it finds any markup errors, it reports them and then aborts.
146
147 Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
148 and the zipball. Double-check with "svn status", then create an SVN tagged
149 copy:
150
151 svn copy svn://vcs.exim.org/pcre/code/trunk \
152 svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
153
154 Don't forget to update Freshmeat when the new release is out, and to tell
155 webmaster@pcre.org and the mailing list. Also, update the list of version
156 numbers in Bugzilla (edit products).
157
158
159 Future ideas (wish list)
160 ========================
161
162 This section records a list of ideas so that they do not get forgotten. They
163 vary enormously in their usefulness and potential for implementation. Some are
164 very sensible; some are rather wacky. Some have been on this list for years;
165 others are relatively new.
166
167 . Optimization
168
169 There are always ideas for new optimizations so as to speed up pattern
170 matching. Most of them try to save work by recognizing a non-match without
171 having to scan all the possibilities. These are some that I've recorded:
172
173 * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
174 slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
175 OTOH, this is pathological - the user could easily fix it.
176
177 * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
178 to have little effect, and maybe makes things worse.
179
180 * "Ends with literal string" - note that a single character doesn't gain much
181 over the existing "required byte" (reqbyte) feature that just remembers one
182 byte.
183
184 * These probably need to go in pcre_study():
185
186 o Remember an initial string rather than just 1 char?
187
188 o A required byte from alternatives - not just the last char, but an
189 earlier one if common to all alternatives.
190
191 o Friedl contains other ideas.
192
193 * pcre_study() does not set initial byte flags for Unicode property types
194 such as \p; I don't know how much benefit there would be for, for example,
195 setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
196 \p{N}.
197
198 * There is scope for more "auto-possessifying" in connection with \p and \P.
199
200 . If Perl gets to a consistent state over the settings of capturing sub-
201 patterns inside repeats, see if we can match it. One example of the
202 difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
203 leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
204 because I think it needs much more state to be remembered.
205
206 . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
207
208 . Unicode
209
210 * There has been a request for direct support of 16-bit characters and
211 UTF-16 (Bugzilla #1049). However, since Unicode is moving beyond purely
212 16-bit characters, is this worth it at all? One possible way of handling
213 16-bit characters would be to "load" them in the same way that UTF-8
214 characters are loaded. Another possibility is to provide a set of
215 translation functions, and build an index during translation so that the
216 returned offsets can automatically be translated (using the index) after a
217 match.
218
219 * A different approach to Unicode might be to use a typedef to do everything
220 in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
221 new typedef to distinguish data from bits of compiled pattern that are in
222 bytes, I think. There would need to be conversion functions in and out. I
223 don't think this is particularly trivial - and anyway, Unicode now has
224 characters that need more than 16 bits, so is this at all sensible? I
225 suspect not.
226
227 . Allow errorptr and erroroffset to be NULL. I don't like this idea.
228
229 . Line endings:
230
231 * Option to use NUL as a line terminator in subject strings. This could now
232 be done relatively easily since the extension to support LF, CR, and CRLF.
233 If it is done, a suitable option for pcregrep is also required.
234
235 . Option to provide the pattern with a length instead of with a NUL terminator.
236 This affects quite a few places in the code and is not trivial.
237
238 . Catch SIGSEGV for stack overflows?
239
240 . A feature to suspend a match via a callout was once requested.
241
242 . Option to convert results into character offsets and character lengths.
243
244 . Option for pcregrep to scan only the start of a file. I am not keen - this is
245 the job of "head".
246
247 . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
248 preceded by a blank line, instead of adding it to every matched line, and (b)
249 support --outputfile=name.
250
251 . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
252
253 . Add a user pointer to pcre_malloc/free functions -- some option would be
254 needed to retain backward compatibility.
255
256 . Define a union for the results from pcre_fullinfo().
257
258 . Provide a "random access to the subject" facility so that the way in which it
259 is stored is independent of PCRE. For efficiency, it probably isn't possible
260 to switch this dynamically. It would have to be specified when PCRE was
261 compiled. PCRE would then call a function every time it wanted a character.
262
263 . Wild thought: the ability to compile from PCRE's internal byte code to a real
264 FSM and a very fast (third) matcher to process the result. There would be
265 even more restrictions than for pcre_dfa_exec(), however. This is not easy.
266
267 . Should pcretest have some private locale data, to avoid relying on the
268 available locales for the test data, since different OS have different ideas?
269 This won't be as thorough a test, but perhaps that doesn't really matter.
270
271 . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
272 them will of course slow it down.
273
274 . Someone suggested --disable-callout to save code space when callouts are
275 never wanted. This seems rather marginal.
276
277 . Check names that consist entirely of digits: PCRE allows, but do Perl and
278 Python, etc?
279
280 . A user suggested a parameter to limit the length of string matched, for
281 example if the parameter is N, the current match should fail if the matched
282 substring exceeds N. This could apply to both match functions. The value
283 could be a new field in the extra block.
284
285 . Callouts with arguments: (?Cn:ARG) for instance.
286
287 . A user is going to supply a patch to generalize the API for user-specific
288 memory allocation so that it is more flexible in threaded environments. This
289 was promised a long time ago, and never appeared...
290
291 . Write a function that generates random matching strings for a compiled regex.
292
293 . Write a wrapper to maintain a structure with specified runtime parameters,
294 such as recurse limit, and pass these to PCRE each time it is called. Also
295 maybe malloc and free. A user sent a prototype.
296
297 . Pcregrep: an option to specify the output line separator, either as a string
298 or select from a fixed list. This is not dead easy, because at the moment it
299 outputs whatever is in the input file.
300
301 . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
302 non-thread-safe patch showed that this can help performance for patterns
303 where there are many alternatives. However, a simple thread-safe
304 implementation that I tried made things worse in many simple cases, so this
305 is not an obviously good thing.
306
307 . Make the longest lookbehind available via pcre_fullinfo(). This is not
308 straightforward because lookbehinds can be nested inside lookbehinds. This
309 case will have to be identified, and the amounts added. This should then give
310 the maximum possible lookbehind length. The reason for wanting this is to
311 help when implementing multi-segment matching using pcre_exec() with partial
312 matching and overlapping segments.
313
314 . PCRE cannot at present distinguish between subpatterns with different names,
315 but the same number (created by the use of ?|). In order to do so, a way of
316 remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
317 Now that (*MARK) has been implemented, it can perhaps be used as a way round
318 this problem.
319
320 . Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
321 "something" and the the #ifdef appears only in one place, in "something".
322
323 Philip Hazel
324 Email local part: ph10
325 Email domain: cam.ac.uk
326 Last updated: 02 August 2011

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