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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 ---------------- 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 . 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, 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 . 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 Making a PCRE release
139 =====================
140
141 Run PrepareRelease and commit the files that it changes (by removing trailing
142 spaces). The first thing this script does is to run CheckMan on the man pages;
143 if it finds any markup errors, it reports them and then aborts.
144
145 Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
146 and the zipball. Double-check with "svn status", then create an SVN tagged
147 copy:
148
149 svn copy svn://vcs.exim.org/pcre/code/trunk \
150 svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
151
152 Don't forget to update Freshmeat when the new release is out, and to tell
153 webmaster@pcre.org and the mailing list. Also, update the list of version
154 numbers in Bugzilla (edit products).
155
156
157 Future ideas (wish list)
158 ========================
159
160 This section records a list of ideas so that they do not get forgotten. They
161 vary enormously in their usefulness and potential for implementation. Some are
162 very sensible; some are rather wacky. Some have been on this list for years;
163 others are relatively new.
164
165 . Optimization
166
167 There are always ideas for new optimizations so as to speed up pattern
168 matching. Most of them try to save work by recognizing a non-match without
169 having to scan all the possibilities. These are some that I've recorded:
170
171 * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
172 slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
173 OTOH, this is pathological - the user could easily fix it.
174
175 * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
176 to have little effect, and maybe makes things worse.
177
178 * "Ends with literal string" - note that a single character doesn't gain much
179 over the existing "required byte" (reqbyte) feature that just remembers one
180 byte.
181
182 * These probably need to go in pcre_study():
183
184 o Remember an initial string rather than just 1 char?
185
186 o A required byte from alternatives - not just the last char, but an
187 earlier one if common to all alternatives.
188
189 o Friedl contains other ideas.
190
191 * pcre_study() does not set initial byte flags for Unicode property types
192 such as \p; I don't know how much benefit there would be for, for example,
193 setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
194 \p{N}.
195
196 * There is scope for more "auto-possessifying" in connection with \p and \P.
197
198 . If Perl gets to a consistent state over the settings of capturing sub-
199 patterns inside repeats, see if we can match it. One example of the
200 difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
201 leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
202 because I think it needs much more state to be remembered.
203
204 . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
205
206 . Unicode
207
208 * There has been a request for direct support of 16-bit characters and
209 UTF-16 (Bugzilla #1049). However, since Unicode is moving beyond purely
210 16-bit characters, is this worth it at all? One possible way of handling
211 16-bit characters would be to "load" them in the same way that UTF-8
212 characters are loaded. Another possibility is to provide a set of
213 translation functions, and build an index during translation so that the
214 returned offsets can automatically be translated (using the index) after a
215 match.
216
217 * A different approach to Unicode might be to use a typedef to do everything
218 in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
219 new typedef to distinguish data from bits of compiled pattern that are in
220 bytes, I think. There would need to be conversion functions in and out. I
221 don't think this is particularly trivial - and anyway, Unicode now has
222 characters that need more than 16 bits, so is this at all sensible? I
223 suspect not.
224
225 . Allow errorptr and erroroffset to be NULL. I don't like this idea.
226
227 . Line endings:
228
229 * Option to use NUL as a line terminator in subject strings. This could now
230 be done relatively easily since the extension to support LF, CR, and CRLF.
231 If it is done, a suitable option for pcregrep is also required.
232
233 . Option to provide the pattern with a length instead of with a NUL terminator.
234 This affects quite a few places in the code and is not trivial.
235
236 . Catch SIGSEGV for stack overflows?
237
238 . A feature to suspend a match via a callout was once requested.
239
240 . Option to convert results into character offsets and character lengths.
241
242 . Option for pcregrep to scan only the start of a file. I am not keen - this is
243 the job of "head".
244
245 . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
246 preceded by a blank line, instead of adding it to every matched line, and (b)
247 support --outputfile=name.
248
249 . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
250
251 . Add a user pointer to pcre_malloc/free functions -- some option would be
252 needed to retain backward compatibility.
253
254 . Define a union for the results from pcre_fullinfo().
255
256 . Provide a "random access to the subject" facility so that the way in which it
257 is stored is independent of PCRE. For efficiency, it probably isn't possible
258 to switch this dynamically. It would have to be specified when PCRE was
259 compiled. PCRE would then call a function every time it wanted a character.
260
261 . Wild thought: the ability to compile from PCRE's internal byte code to a real
262 FSM and a very fast (third) matcher to process the result. There would be
263 even more restrictions than for pcre_dfa_exec(), however. This is not easy.
264
265 . Should pcretest have some private locale data, to avoid relying on the
266 available locales for the test data, since different OS have different ideas?
267 This won't be as thorough a test, but perhaps that doesn't really matter.
268
269 . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
270 them will of course slow it down.
271
272 . Someone suggested --disable-callout to save code space when callouts are
273 never wanted. This seems rather marginal.
274
275 . Check names that consist entirely of digits: PCRE allows, but do Perl and
276 Python, etc?
277
278 . A user suggested a parameter to limit the length of string matched, for
279 example if the parameter is N, the current match should fail if the matched
280 substring exceeds N. This could apply to both match functions. The value
281 could be a new field in the extra block.
282
283 . Callouts with arguments: (?Cn:ARG) for instance.
284
285 . A user is going to supply a patch to generalize the API for user-specific
286 memory allocation so that it is more flexible in threaded environments. This
287 was promised a long time ago, and never appeared...
288
289 . Write a function that generates random matching strings for a compiled regex.
290
291 . Write a wrapper to maintain a structure with specified runtime parameters,
292 such as recurse limit, and pass these to PCRE each time it is called. Also
293 maybe malloc and free. A user sent a prototype.
294
295 . Pcregrep: an option to specify the output line separator, either as a string
296 or select from a fixed list. This is not dead easy, because at the moment it
297 outputs whatever is in the input file.
298
299 . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
300 non-thread-safe patch showed that this can help performance for patterns
301 where there are many alternatives. However, a simple thread-safe
302 implementation that I tried made things worse in many simple cases, so this
303 is not an obviously good thing.
304
305 . Make the longest lookbehind available via pcre_fullinfo(). This is not
306 straightforward because lookbehinds can be nested inside lookbehinds. This
307 case will have to be identified, and the amounts added. This should then give
308 the maximum possible lookbehind length. The reason for wanting this is to
309 help when implementing multi-segment matching using pcre_exec() with partial
310 matching and overlapping segments.
311
312 . PCRE cannot at present distinguish between subpatterns with different names,
313 but the same number (created by the use of ?|). In order to do so, a way of
314 remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
315 Now that (*MARK) has been implemented, it can perhaps be used as a way round
316 this problem.
317
318 . Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
319 "something" and the the #ifdef appears only in one place, in "something".
320
321 Philip Hazel
322 Email local part: ph10
323 Email domain: cam.ac.uk
324 Last updated: 12 January 2011

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