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Final tidies for 8.31.
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 . Update the library version numbers in configure.ac according to the rules
105 given below.
106
107 . If new build options have been added, ensure that they are added to the CMake
108 files as well as to the autoconf files. The relevant files are CMakeLists.txt
109 and config-cmake.h.in. After making a release tarball, test it out with CMake
110 if there have been changes here.
111
112 . Run ./autogen.sh to ensure everything is up-to-date.
113
114 . Compile and test with many different config options, and combinations of
115 options. Also, test with valgrind by running "RunTest valgrind" and
116 "RunGrepTest valgrind" (which takes quite a long time). The script
117 maint/ManyConfigTests now encapsulates this testing. It runs tests with
118 different configurations, and it also runs some of them with valgrind, all of
119 which can take quite some time.
120
121 . Run perltest.pl on the test data for tests 1, 4, and 6. The output
122 should match the PCRE test output, apart from the version identification at
123 the start of each test. The other tests are not Perl-compatible (they use
124 various PCRE-specific features or options).
125
126 . It is possible to test with the emulated memmove() function by undefining
127 HAVE_MEMMOVE and HAVE_BCOPY in config.h, though I do not do this often. You
128 may see a number of "pcre_memmove defined but not used" warnings for the
129 modules in which there is no call to memmove(). These can be ignored.
130
131 . Documentation: check AUTHORS, ChangeLog (check version and date), LICENCE,
132 NEWS (check version and date), NON-AUTOTOOLS-BUILD, and README. Many of these
133 won't need changing, but over the long term things do change.
134
135 . I used to test new releases myself on a number of different operating
136 systems, using different compilers as well. For example, on Solaris it is
137 helpful to test using Sun's cc compiler as a change from gcc. Adding
138 -xarch=v9 to the cc options does a 64-bit test, but it also needs -S 64 for
139 pcretest to increase the stack size for test 2. Since I retired I can no
140 longer do this, but instead I rely on putting out release candidates for
141 folks on the pcre-dev list to test.
142
143
144 Updating version info for libtool
145 =================================
146
147 This set of rules for updating library version information came from a web page
148 whose URL I have forgotten. The version information consists of three parts:
149 (current, revision, age).
150
151 1. Start with version information of 0:0:0 for each libtool library.
152
153 2. Update the version information only immediately before a public release of
154 your software. More frequent updates are unnecessary, and only guarantee
155 that the current interface number gets larger faster.
156
157 3. If the library source code has changed at all since the last update, then
158 increment revision; c:r:a becomes c:r+1:a.
159
160 4. If any interfaces have been added, removed, or changed since the last
161 update, increment current, and set revision to 0.
162
163 5. If any interfaces have been added since the last public release, then
164 increment age.
165
166 6. If any interfaces have been removed or changed since the last public
167 release, then set age to 0.
168
169 The following explanation may help in understanding the above rules a bit
170 better. Consider that there are three possible kinds of reaction from users to
171 changes in a shared library:
172
173 1. Programs using the previous version may use the new version as a drop-in
174 replacement, and programs using the new version can also work with the
175 previous one. In other words, no recompiling nor relinking is needed. In
176 this case, increment revision only, don't touch current or age.
177
178 2. Programs using the previous version may use the new version as a drop-in
179 replacement, but programs using the new version may use APIs not present in
180 the previous one. In other words, a program linking against the new version
181 may fail if linked against the old version at run time. In this case, set
182 revision to 0, increment current and age.
183
184 3. Programs may need to be changed, recompiled, relinked in order to use the
185 new version. Increment current, set revision and age to 0.
186
187
188 Making a PCRE release
189 =====================
190
191 Run PrepareRelease and commit the files that it changes (by removing trailing
192 spaces). The first thing this script does is to run CheckMan on the man pages;
193 if it finds any markup errors, it reports them and then aborts.
194
195 Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
196 and the zipball. Double-check with "svn status", then create an SVN tagged
197 copy:
198
199 svn copy svn://vcs.exim.org/pcre/code/trunk \
200 svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
201
202 Don't forget to update Freshmeat when the new release is out, and to tell
203 webmaster@pcre.org and the mailing list. Also, update the list of version
204 numbers in Bugzilla (edit products).
205
206
207 Future ideas (wish list)
208 ========================
209
210 This section records a list of ideas so that they do not get forgotten. They
211 vary enormously in their usefulness and potential for implementation. Some are
212 very sensible; some are rather wacky. Some have been on this list for years;
213 others are relatively new.
214
215 . Optimization
216
217 There are always ideas for new optimizations so as to speed up pattern
218 matching. Most of them try to save work by recognizing a non-match without
219 having to scan all the possibilities. These are some that I've recorded:
220
221 * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
222 slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
223 OTOH, this is pathological - the user could easily fix it.
224
225 * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
226 to have little effect, and maybe makes things worse.
227
228 * "Ends with literal string" - note that a single character doesn't gain much
229 over the existing "required byte" (reqbyte) feature that just remembers one
230 data unit.
231
232 * These probably need to go in pcre_study():
233
234 o Remember an initial string rather than just 1 char?
235
236 o A required data unit from alternatives - not just the last unit, but an
237 earlier one if common to all alternatives.
238
239 o Friedl contains other ideas.
240
241 * pcre_study() does not set initial byte flags for Unicode property types
242 such as \p; I don't know how much benefit there would be for, for example,
243 setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
244 \p{N}.
245
246 * There is scope for more "auto-possessifying" in connection with \p and \P.
247
248 . If Perl gets to a consistent state over the settings of capturing sub-
249 patterns inside repeats, see if we can match it. One example of the
250 difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
251 leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
252 because I think it needs much more state to be remembered.
253
254 . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
255
256 . Allow errorptr and erroroffset to be NULL. I don't like this idea.
257
258 . Line endings:
259
260 * Option to use NUL as a line terminator in subject strings. This could now
261 be done relatively easily since the extension to support LF, CR, and CRLF.
262 If it is done, a suitable option for pcregrep is also required.
263
264 . Option to provide the pattern with a length instead of with a NUL terminator.
265 This affects quite a few places in the code and is not trivial.
266
267 . Catch SIGSEGV for stack overflows?
268
269 . A feature to suspend a match via a callout was once requested.
270
271 . Option to convert results into character offsets and character lengths.
272
273 . Option for pcregrep to scan only the start of a file. I am not keen - this is
274 the job of "head".
275
276 . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
277 preceded by a blank line, instead of adding it to every matched line, and (b)
278 support --outputfile=name.
279
280 . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
281 (And now presumably UTF-16 and UCP for the 16-bit library.)
282
283 . Add a user pointer to pcre_malloc/free functions -- some option would be
284 needed to retain backward compatibility.
285
286 . Define a union for the results from pcre_fullinfo().
287
288 . Provide a "random access to the subject" facility so that the way in which it
289 is stored is independent of PCRE. For efficiency, it probably isn't possible
290 to switch this dynamically. It would have to be specified when PCRE was
291 compiled. PCRE would then call a function every time it wanted a character.
292
293 . Wild thought: the ability to compile from PCRE's internal byte code to a real
294 FSM and a very fast (third) matcher to process the result. There would be
295 even more restrictions than for pcre_dfa_exec(), however. This is not easy.
296 This is probably obsolete now that we have the JIT support.
297
298 . Should pcretest have some private locale data, to avoid relying on the
299 available locales for the test data, since different OS have different ideas?
300 This won't be as thorough a test, but perhaps that doesn't really matter.
301
302 . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
303 them will of course slow it down.
304
305 . Someone suggested --disable-callout to save code space when callouts are
306 never wanted. This seems rather marginal.
307
308 . Check names that consist entirely of digits: PCRE allows, but do Perl and
309 Python, etc?
310
311 . A user suggested a parameter to limit the length of string matched, for
312 example if the parameter is N, the current match should fail if the matched
313 substring exceeds N. This could apply to both match functions. The value
314 could be a new field in the extra block.
315
316 . Callouts with arguments: (?Cn:ARG) for instance.
317
318 . A user is going to supply a patch to generalize the API for user-specific
319 memory allocation so that it is more flexible in threaded environments. This
320 was promised a long time ago, and never appeared. However, this is a live
321 issue not only for threaded environments, but for libraries that use PCRE and
322 want not to be beholden to their caller's memory allocation.
323
324 . Write a wrapper to maintain a structure with specified runtime parameters,
325 such as recurse limit, and pass these to PCRE each time it is called. Also
326 maybe malloc and free. A user sent a prototype. This relates the the previous
327 item.
328
329 . Write a function that generates random matching strings for a compiled regex.
330
331 . Pcregrep: an option to specify the output line separator, either as a string
332 or select from a fixed list. This is not dead easy, because at the moment it
333 outputs whatever is in the input file.
334
335 . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
336 non-thread-safe patch showed that this can help performance for patterns
337 where there are many alternatives. However, a simple thread-safe
338 implementation that I tried made things worse in many simple cases, so this
339 is not an obviously good thing.
340
341 . Make the longest lookbehind available via pcre_fullinfo(). This is not
342 straightforward because lookbehinds can be nested inside lookbehinds. This
343 case will have to be identified, and the amounts added. This should then give
344 the maximum possible lookbehind length. The reason for wanting this is to
345 help when implementing multi-segment matching using pcre_exec() with partial
346 matching and overlapping segments.
347
348 . PCRE cannot at present distinguish between subpatterns with different names,
349 but the same number (created by the use of ?|). In order to do so, a way of
350 remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
351 Now that (*MARK) has been implemented, it can perhaps be used as a way round
352 this problem.
353
354 . Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
355 "something" and the the #ifdef appears only in one place, in "something".
356
357 Philip Hazel
358 Email local part: ph10
359 Email domain: cam.ac.uk
360 Last updated: 18 June 2012

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