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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 GenerateUtt.py A Python script to generate part of the pcre_tables.c file
20 that contains Unicode script names in a long string with
21 offsets, which is tedious to maintain by hand.
22
23 ManyConfigTests A shell script that runs "configure, make, test" a number of
24 times with different configuration settings.
25
26 MultiStage2.py A Python script that generates the file pcre_ucd.c from three
27 Unicode data tables, which are themselves downloaded from the
28 Unicode web site. Run this script in the "maint" directory.
29 The generated file contains the tables for a 2-stage lookup
30 of Unicode properties.
31
32 pcre_chartables.c.non-standard
33 This is a set of character tables that came from a Windows
34 system. It has characters greater than 128 that are set as
35 spaces, amongst other things. I kept it so that it can be
36 used for testing from time to time.
37
38 README This file.
39
40 Unicode.tables The files in this directory (CaseFolding.txt,
41 DerivedGeneralCategory.txt, GraphemeBreakProperty.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 If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
74 the cause is usually a missing (or misspelt) name in the list of scripts. I
75 couldn't find a straightforward list of scripts on the Unicode site, but
76 there's a useful Wikipedia page that list them, and notes the Unicode version
77 in which they were introduced:
78
79 http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts
80
81 The ucptest program can be compiled and used to check that the new tables in
82 pcre_ucd.c work properly, using the data files in ucptestdata to check a number
83 of test characters. The source file ucptest.c must be updated whenever new
84 Unicode script names are added.
85
86 Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
87 of Unicode script names.
88
89
90 Preparing for a PCRE release
91 ============================
92
93 This section contains a checklist of things that I consult before building a
94 distribution for a new release.
95
96 . Ensure that the version number and version date are correct in configure.ac.
97
98 . Update the library version numbers in configure.ac according to the rules
99 given below.
100
101 . If new build options have been added, ensure that they are added to the CMake
102 files as well as to the autoconf files. The relevant files are CMakeLists.txt
103 and config-cmake.h.in. After making a release tarball, test it out with CMake
104 if there have been changes here.
105
106 . Run ./autogen.sh to ensure everything is up-to-date.
107
108 . Compile and test with many different config options, and combinations of
109 options. Also, test with valgrind by running "RunTest valgrind" and
110 "RunGrepTest valgrind" (which takes quite a long time). The script
111 maint/ManyConfigTests now encapsulates this testing. It runs tests with
112 different configurations, and it also runs some of them with valgrind, all of
113 which can take quite some time.
114
115 . Run perltest.pl on the test data for tests 1, 4, and 6. The output
116 should match the PCRE test output, apart from the version identification at
117 the start of each test. The other tests are not Perl-compatible (they use
118 various PCRE-specific features or options).
119
120 . It is possible to test with the emulated memmove() function by undefining
121 HAVE_MEMMOVE and HAVE_BCOPY in config.h, though I do not do this often. You
122 may see a number of "pcre_memmove defined but not used" warnings for the
123 modules in which there is no call to memmove(). These can be ignored.
124
125 . Documentation: check AUTHORS, ChangeLog (check version and date), LICENCE,
126 NEWS (check version and date), NON-AUTOTOOLS-BUILD, and README. Many of these
127 won't need changing, but over the long term things do change.
128
129 . I used to test new releases myself on a number of different operating
130 systems, using different compilers as well. For example, on Solaris it is
131 helpful to test using Sun's cc compiler as a change from gcc. Adding
132 -xarch=v9 to the cc options does a 64-bit test, but it also needs -S 64 for
133 pcretest to increase the stack size for test 2. Since I retired I can no
134 longer do this, but instead I rely on putting out release candidates for
135 folks on the pcre-dev list to test.
136
137
138 Updating version info for libtool
139 =================================
140
141 This set of rules for updating library version information came from a web page
142 whose URL I have forgotten. The version information consists of three parts:
143 (current, revision, age).
144
145 1. Start with version information of 0:0:0 for each libtool library.
146
147 2. Update the version information only immediately before a public release of
148 your software. More frequent updates are unnecessary, and only guarantee
149 that the current interface number gets larger faster.
150
151 3. If the library source code has changed at all since the last update, then
152 increment revision; c:r:a becomes c:r+1:a.
153
154 4. If any interfaces have been added, removed, or changed since the last
155 update, increment current, and set revision to 0.
156
157 5. If any interfaces have been added since the last public release, then
158 increment age.
159
160 6. If any interfaces have been removed or changed since the last public
161 release, then set age to 0.
162
163 The following explanation may help in understanding the above rules a bit
164 better. Consider that there are three possible kinds of reaction from users to
165 changes in a shared library:
166
167 1. Programs using the previous version may use the new version as a drop-in
168 replacement, and programs using the new version can also work with the
169 previous one. In other words, no recompiling nor relinking is needed. In
170 this case, increment revision only, don't touch current or age.
171
172 2. Programs using the previous version may use the new version as a drop-in
173 replacement, but programs using the new version may use APIs not present in
174 the previous one. In other words, a program linking against the new version
175 may fail if linked against the old version at run time. In this case, set
176 revision to 0, increment current and age.
177
178 3. Programs may need to be changed, recompiled, relinked in order to use the
179 new version. Increment current, set revision and age to 0.
180
181
182 Making a PCRE release
183 =====================
184
185 Run PrepareRelease and commit the files that it changes (by removing trailing
186 spaces). The first thing this script does is to run CheckMan on the man pages;
187 if it finds any markup errors, it reports them and then aborts.
188
189 Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
190 and the zipball. Double-check with "svn status", then create an SVN tagged
191 copy:
192
193 svn copy svn://vcs.exim.org/pcre/code/trunk \
194 svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
195
196 Don't forget to update Freshmeat when the new release is out, and to tell
197 webmaster@pcre.org and the mailing list. Also, update the list of version
198 numbers in Bugzilla (edit products).
199
200
201 Future ideas (wish list)
202 ========================
203
204 This section records a list of ideas so that they do not get forgotten. They
205 vary enormously in their usefulness and potential for implementation. Some are
206 very sensible; some are rather wacky. Some have been on this list for years;
207 others are relatively new.
208
209 . Optimization
210
211 There are always ideas for new optimizations so as to speed up pattern
212 matching. Most of them try to save work by recognizing a non-match without
213 having to scan all the possibilities. These are some that I've recorded:
214
215 * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
216 slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
217 OTOH, this is pathological - the user could easily fix it.
218
219 * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
220 to have little effect, and maybe makes things worse.
221
222 * "Ends with literal string" - note that a single character doesn't gain much
223 over the existing "required byte" (reqbyte) feature that just remembers one
224 data unit.
225
226 * These probably need to go in pcre_study():
227
228 o Remember an initial string rather than just 1 char?
229
230 o A required data unit from alternatives - not just the last unit, but an
231 earlier one if common to all alternatives.
232
233 o Friedl contains other ideas.
234
235 * pcre_study() does not set initial byte flags for Unicode property types
236 such as \p; I don't know how much benefit there would be for, for example,
237 setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
238 \p{N}.
239
240 * There is scope for more "auto-possessifying" in connection with \p and \P.
241
242 . If Perl gets to a consistent state over the settings of capturing sub-
243 patterns inside repeats, see if we can match it. One example of the
244 difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
245 leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
246 because I think it needs much more state to be remembered.
247
248 . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
249
250 . Allow errorptr and erroroffset to be NULL. I don't like this idea.
251
252 . Line endings:
253
254 * Option to use NUL as a line terminator in subject strings. This could now
255 be done relatively easily since the extension to support LF, CR, and CRLF.
256 If it is done, a suitable option for pcregrep is also required.
257
258 . Option to provide the pattern with a length instead of with a NUL terminator.
259 This affects quite a few places in the code and is not trivial.
260
261 . Catch SIGSEGV for stack overflows?
262
263 . A feature to suspend a match via a callout was once requested.
264
265 . Option to convert results into character offsets and character lengths.
266
267 . Option for pcregrep to scan only the start of a file. I am not keen - this is
268 the job of "head".
269
270 . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
271 preceded by a blank line, instead of adding it to every matched line, and (b)
272 support --outputfile=name.
273
274 . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
275 (And now presumably UTF-16 and UCP for the 16-bit library, and UTF-32 and UCP
276 for the 32-bit library.)
277
278 . Add a user pointer to pcre_malloc/free functions -- some option would be
279 needed to retain backward compatibility.
280
281 . Define a union for the results from pcre_fullinfo().
282
283 . Provide a "random access to the subject" facility so that the way in which it
284 is stored is independent of PCRE. For efficiency, it probably isn't possible
285 to switch this dynamically. It would have to be specified when PCRE was
286 compiled. PCRE would then call a function every time it wanted a character.
287
288 . Wild thought: the ability to compile from PCRE's internal byte code to a real
289 FSM and a very fast (third) matcher to process the result. There would be
290 even more restrictions than for pcre_dfa_exec(), however. This is not easy.
291 This is probably obsolete now that we have the JIT support.
292
293 . Should pcretest have some private locale data, to avoid relying on the
294 available locales for the test data, since different OS have different ideas?
295 This won't be as thorough a test, but perhaps that doesn't really matter.
296
297 . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
298 them will of course slow it down.
299
300 . Someone suggested --disable-callout to save code space when callouts are
301 never wanted. This seems rather marginal.
302
303 . Check names that consist entirely of digits: PCRE allows, but do Perl and
304 Python, etc?
305
306 . A user suggested a parameter to limit the length of string matched, for
307 example if the parameter is N, the current match should fail if the matched
308 substring exceeds N. This could apply to both match functions. The value
309 could be a new field in the extra block.
310
311 . Callouts with arguments: (?Cn:ARG) for instance.
312
313 . A user is going to supply a patch to generalize the API for user-specific
314 memory allocation so that it is more flexible in threaded environments. This
315 was promised a long time ago, and never appeared. However, this is a live
316 issue not only for threaded environments, but for libraries that use PCRE and
317 want not to be beholden to their caller's memory allocation.
318
319 . Write a wrapper to maintain a structure with specified runtime parameters,
320 such as recurse limit, and pass these to PCRE each time it is called. Also
321 maybe malloc and free. A user sent a prototype. This relates the the previous
322 item.
323
324 . Write a function that generates random matching strings for a compiled regex.
325
326 . Pcregrep: an option to specify the output line separator, either as a string
327 or select from a fixed list. This is not dead easy, because at the moment it
328 outputs whatever is in the input file.
329
330 . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
331 non-thread-safe patch showed that this can help performance for patterns
332 where there are many alternatives. However, a simple thread-safe
333 implementation that I tried made things worse in many simple cases, so this
334 is not an obviously good thing.
335
336 . PCRE cannot at present distinguish between subpatterns with different names,
337 but the same number (created by the use of ?|). In order to do so, a way of
338 remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
339 Now that (*MARK) has been implemented, it can perhaps be used as a way round
340 this problem.
341
342 . Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
343 "something" and the the #ifdef appears only in one place, in "something".
344
345 Philip Hazel
346 Email local part: ph10
347 Email domain: cam.ac.uk
348 Last updated: 07 December 2012

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