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Documentation update preparatory to 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 Builducptable A Perl script that creates the contents of the ucptable.h file
20 from two Unicode data files, which themselves are downloaded
21 from the Unicode web site. Run this script in the "maint"
22 directory.
23
24 ManyConfigTests A shell script that runs "configure, make, test" a number of
25 times with different configuration settings.
26
27 Unicode.tables The files in this directory, Scripts.txt and UnicodeData.txt,
28 were downloaded from the Unicode web site. They contain
29 information about Unicode characters and scripts.
30
31 ucptest.c A short C program for testing the Unicode property functions
32 in pcre_ucp_searchfuncs.c, mainly useful after rebuilding the
33 Unicode property table. Compile and run this in the "maint"
34 directory.
35
36 ucptestdata A directory containing two files, testinput1 and testoutput1,
37 to use in conjunction with the ucptest program.
38
39 utf8.c A short, freestanding C program for converting a Unicode code
40 point into a sequence of bytes in the UTF-8 encoding, and vice
41 versa. If its argument is a hex number such as 0x1234, it
42 outputs a list of the equivalent UTF-8 bytes. If its argument
43 is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
44 treats them as a UTF-8 character and outputs the equivalent
45 code point in hex.
46
47
48 Updating to a new Unicode release
49 ---------------------------------
50
51 When there is a new release of Unicode, the files in Unicode.tables must be
52 refreshed from the web site, and the Buildupctable script can then be run to
53 generate a new version of ucptable.h. The ucptest program can be used to check
54 that the resulting table works properly, using the data files in ucptestdata to
55 check a number of test characters.
56
57
58 Preparing for a PCRE release
59 ----------------------------
60
61 This section contains a checklist of things that I consult before building a
62 distribution for a new release.
63
64 . Ensure that the version number and version date are correct in configure.ac,
65 ChangeLog, and NEWS.
66
67 . Run ./autogen.sh to ensure everything is up-to-date.
68
69 . Compile and test with many different config options, and combinations of
70 options. The maint/ManyConfigTests script now encapsulates this testing.
71
72 . Run perltest.pl on the test data for tests 1 and 4. The output should match
73 the PCRE test output, apart from the version identification at the top. The
74 other tests are not Perl-compatible (they use various special PCRE options).
75
76 . Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
77 valgrind", though that takes quite a long time.
78
79 . It may also useful to test with Electric Fence, though the fact that it
80 grumbles for missing free() calls can be a nuisance. (A missing free() in
81 pcretest is hardly a big problem.) To build with EF, use:
82
83 LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
84
85 Then all normal runs use it to check for buffer overflow. Also run everything
86 with:
87
88 EF_PROTECT_BELOW=1 <whatever>
89
90 because there have been problems with lookbehinds that looked too far.
91
92 . Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
93 HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
94 used" warnings for the modules in which there is no call to memmove(). These
95 can be ignored.
96
97 . Documentation: check AUTHORS, COPYING, ChangeLog (check date), INSTALL,
98 LICENCE, NEWS (check date), NON-UNIX-USE, and README. Many of these won't
99 need changing, but over the long term things do change.
100
101 . Man pages: Check all man pages for \ not followed by e or f or " because
102 that indicates a markup error.
103
104 . When the release is built, test it on a number of different operating
105 systems if possible, and using different compilers as well. For example,
106 on Solaris it is helpful to test using Sun's cc compiler as a change from
107 gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
108 needs -S 64 for pcretest to increase the stack size for test 2.
109
110
111 Making a PCRE release
112 ---------------------
113
114 Run PrepareRelease and commit the files that it changes (by removing trailing
115 spaces). Then run "make distcheck" to create the tarballs and the zipball.
116
117 Don't forget to update Freshmeat when the new release is out, and to tell
118 webmaster@pcre.org and the mailing list.
119
120
121 Future ideas (wish list)
122 ------------------------
123
124 This section records a list of ideas so that they do not get forgotten. They
125 vary enormously in their usefulness and potential for implementation. Some are
126 very sensible; some are rather wacky. Some have been on this list for years;
127 others are relatively new.
128
129 . Optimization
130
131 There are always ideas for new optimizations so as to speed up pattern
132 matching. Most of them try to save work by recognizing a non-match without
133 having to scan all the possibilities. These are some that I've recorded:
134
135 * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
136 slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
137 OTOH, this is pathological - the user could easily fix it.
138
139 * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
140 to have little effect, and maybe makes things worse.
141
142 * "Ends with literal string" - note that a single character doesn't gain much
143 over the existing "required byte" (reqbyte) feature that just saves one
144 byte.
145
146 * These probably need to go in study():
147
148 o Remember an initial string rather than just 1 char?
149
150 o A required byte from alternatives - not just the last char, but an
151 earlier one if common to all alternatives.
152
153 o Minimum length of subject needed.
154
155 o Friedl contains other ideas.
156
157 . If Perl gets to a consistent state over the settings of capturing sub-
158 patterns inside repeats, see if we can match it. One example of the
159 difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
160 leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
161 because I think it needs much more state to be remembered.
162
163 . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
164
165 . Unicode
166
167 * Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
168 character classes. For the moment, I've chosen not to support this for
169 backward compatibility, for speed, and because it would be messy to
170 implement.
171
172 * A different approach to Unicode might be to use a typedef to do everything
173 in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
174 new typedef to distinguish data from bits of compiled pattern that are in
175 bytes, I think. There would need to be conversion functions in and out. I
176 don't think this is particularly trivial - and anyway, Unicode now has
177 characters that need more than 16 bits, so is this at all sensible?
178
179 * There has been a request for direct support of 16-bit characters and
180 UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
181 is this worth it at all? One possible way of handling 16-bit characters
182 would be to "load" them in the same way that UTF-8 characters are loaded.
183
184 . Allow errorptr and erroroffset to be NULL. I don't like this idea.
185
186 . Line endings:
187
188 * Option to use NUL as a line terminator in subject strings. This could now
189 be done relatively easily since the extension to support LF, CR, and CRLF.
190 If this is done, a suitable option for pcregrep is also required.
191
192 . Option to provide the pattern with a length instead of with a NUL terminator.
193 This probably affects quite a few places in the code.
194
195 . Catch SIGSEGV for stack overflows?
196
197 . A feature to suspend a match via a callout was once requested.
198
199 . Option to convert results into character offsets and character lengths.
200
201 . Option for pcregrep to scan only the start of a file. I am not keen - this is
202 the job of "head".
203
204 . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
205 preceded by a blank line, instead of adding it to every matched line, and (b)
206 support --outputfile=name.
207
208 . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 7.
209
210 . Add a user pointer to pcre_malloc/free functions -- some option would be
211 needed to retain backward compatibility.
212
213 . Define a union for the results from pcre_fullinfo().
214
215 . Provide a "random access to the subject" facility so that the way in which it
216 is stored is independent of PCRE. For efficiency, it probably isn't possible
217 to switch this dynamically. It would have to be specified when PCRE was
218 compiled. PCRE would then call a function every time it wanted a character.
219
220 . There are new (*PRUNE) facilities in Perl 5.10, some of which it might be
221 relatively easy to implement.
222
223 . Wild thought: the ability to compile from PCRE's internal byte code to a real
224 FSM and a very fast (third) matcher to process the result. There would be
225 even more restrictions than for pcre_dfa_exec(), however. This is not easy.
226
227 . Should pcretest have some private locale data, to avoid relying on the
228 available locales for the test data, since different OS have different ideas?
229 This won't be as thorough a test, but perhaps that doesn't really matter.
230
231 . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
232 them will of course slow it down.
233
234 . Someone suggested --disable-callout to save code space when callouts are
235 never wanted. This seems rather marginal.
236
237 . "Cut" as described in Jeffrey Friedl's book, p364: \v and \V. The definitions
238 aren't yet clear enough for me. \v flushes saved states so that no
239 backtracking to anything earlier can happen; \V says "no more bumpalong", but
240 does it fail the current match? As described in the book, these aren't really
241 "cut" as in Prolog, are they? NOTE: (a) PCRE once had "cut", but it was
242 removed when atomic groups were introduced. (b) Perl 5.10 has some (*PRUNE)
243 features --
244
245 . These are the Perl 5.10 backtracking control features (all of which are
246 described as "experimental" -- some of them "very experimental") that it
247 might be easy to add to PCRE. They all succeed when encountered, but act as
248 follows when backtracking:
249
250 (*PRUNE) fail this match attempt, but still bumpalong
251 (*SKIP) fail this match attempt, bumpalong to current match point
252 (*THEN) fail this branch, try next branch at same level or fail if none
253 (*COMMIT) fail this match attempt, suppress bumpalong
254 (*FAIL) fail and backtrack (same as (?!) and that can be optimized)
255 (*F) synonym for (*FAIL)
256 (*ACCEPT) behave as if end of pattern reached ("very experimental")
257
258 Some of these can have arguments (*PRUNE:NAME) but I'm not sure whether they
259 make sense in the PCRE context.
260
261 Philip Hazel
262 Email local part: ph10
263 Email domain: cam.ac.uk
264 Last updated: 13 June 2007

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