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code/trunk/maintain/README revision 111 by ph10, Thu Mar 8 16:53:09 2007 UTC code/trunk/maint/README revision 507 by ph10, Wed Mar 10 16:08:01 2010 UTC
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1  The files in the "maintain" directory of the PCRE source contain data, scripts,  MAINTENANCE README FOR PCRE
2  and programs that are used for the maintenance of PCRE, but do not form part of  ===========================
3  the PCRE distribution tarballs.  
4    The files in the "maint" directory of the PCRE source contain data, scripts,
5  Builducptable   A Perl script that creates the contents of the ucptable.h file  and programs that are used for the maintenance of PCRE, but which do not form
6                  from two Unicode data files, which themselves are downloaded  part of the PCRE distribution tarballs. This document describes these files and
7                  from the Unicode web site. Run this script in the "maintain"  also contains some notes for maintainers. Its contents are:
8                  directory.  
9      Files in the maint directory
10  Tech.Notes      Some notes about the internals of the PCRE code.    Updating to a new Unicode release
11      Preparing for a PCRE release
12  Unicode.tables  The files in this directory, Scripts.txt and UnicodeData.txt,    Making a PCRE release
13                  were downloaded from the Unicode web site. They contain    Long-term ideas (wish list)
14                  information about Unicode characters and scripts.  
15    
16  ucptest.c       A short C program for testing the Unicode property functions in  Files in the maint directory
17                  pcre_ucp_searchfuncs.c, mainly useful after rebuilding the  ============================
18                  Unicode property table. Compile and run this in the "maintain"  
19                  directory.  ---------------- This file is now OBSOLETE and no longer used ----------------
20    Builducptable    A Perl script that creates the contents of the ucptable.h file
21  ucptestdata     A directory containing two files, testinput1 and testoutput1,                   from two Unicode data files, which themselves are downloaded
22                  to use in conjunction with the ucptest program.                   from the Unicode web site. Run this script in the "maint"
23                     directory.
24  utf8.c          A short, freestanding C program for converting a Unicode code  ---------------- This file is now OBSOLETE and no longer used ----------------
25                  point into a sequence of bytes in the UTF-8 encoding, and vice  
26                  versa. If its argument is a hex number such as 0x1234, it  GenerateUtt.py   A Python script to generate part of the pcre_tables.c file
27                  outputs a list of the equivalent UTF-8 bytes. If its argument                   that contains Unicode script names in a long string with
28                  is sequence of concatenated UTF-8 bytes (e.g. e188b4) it treats                   offsets, which is tedious to maintain by hand.
29                  them as a UTF-8 character and outputs the equivalent code point  
30                  in hex.  ManyConfigTests  A shell script that runs "configure, make, test" a number of
31                     times with different configuration settings.
32  When there is a new release of Unicode, the files in Unicode.tables must be  
33  refreshed from the web site, and the Buildupctable script can then be run to  MultiStage2.py   A Python script that generates the file pcre_ucd.c from three
34  generate a new version of ucptable.h. The ucptest program can be used to check                   Unicode data tables, which are themselves downloaded from the
35  that the resulting table works properly, using the data files in ucptestdata to                   Unicode web site. Run this script in the "maint" directory.
36  check a number of test characters.                   The generated file contains the tables for a 2-stage lookup
37                     of Unicode properties.
38  ****  
39    README           This file.
40    
41    Unicode.tables   The files in this directory, DerivedGeneralCategory.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    . If new build options have been added, ensure that they are added to the CMake
99      files as well as to the autoconf files.
100    
101    . Run ./autogen.sh to ensure everything is up-to-date.
102    
103    . Compile and test with many different config options, and combinations of
104      options. The maint/ManyConfigTests script now encapsulates this testing.
105    
106    . Run perltest.pl on the test data for tests 1, 4, 6, and 11. The first two can
107      be run with Perl 5.8 or 5.10; the last two require Perl 5.10. The output
108      should match the PCRE test output, apart from the version identification at
109      the start of each test. The other tests are not Perl-compatible (they use
110      various PCRE-specific features or options).
111    
112    . Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
113      valgrind", though that takes quite a long time.
114    
115    . It may also useful to test with Electric Fence, though the fact that it
116      grumbles for missing free() calls can be a nuisance. (A missing free() in
117      pcretest is hardly a big problem.) To build with EF, use:
118    
119        LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
120    
121      Then all normal runs use it to check for buffer overflow. Also run everything
122      with:
123    
124        EF_PROTECT_BELOW=1 <whatever>
125    
126      because there have been problems with lookbehinds that looked too far.
127    
128    . Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
129      HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
130      used" warnings for the modules in which there is no call to memmove(). These
131      can be ignored.
132    
133    . Documentation: check AUTHORS, COPYING, ChangeLog (check version and date),
134      INSTALL, LICENCE, NEWS (check version and date), NON-UNIX-USE, and README.
135      Many of these won't need changing, but over the long term things do change.
136    
137    . Man pages: Check all man pages for \ not followed by e or f or " because
138      that indicates a markup error. However, there is one exception: pcredemo.3,
139      which is created from the pcredemo.c program. It contains three instances
140      of \\n.
141    
142    . When the release is built, test it on a number of different operating
143      systems if possible, and using different compilers as well. For example,
144      on Solaris it is helpful to test using Sun's cc compiler as a change from
145      gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
146      needs -S 64 for pcretest to increase the stack size for test 2.
147    
148    
149    Making a PCRE release
150    =====================
151    
152    Run PrepareRelease and commit the files that it changes (by removing trailing
153    spaces). Then run "make distcheck" to create the tarballs and the zipball.
154    Double-check with "svn status", then create an SVN tagged copy:
155    
156      svn copy svn://vcs.exim.org/pcre/code/trunk \
157               svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
158    
159    Don't forget to update Freshmeat when the new release is out, and to tell
160    webmaster@pcre.org and the mailing list. Also, update the list of version
161    numbers in Bugzilla (edit products).
162    
163    
164    Future ideas (wish list)
165    ========================
166    
167    This section records a list of ideas so that they do not get forgotten. They
168    vary enormously in their usefulness and potential for implementation. Some are
169    very sensible; some are rather wacky. Some have been on this list for years;
170    others are relatively new.
171    
172    . Optimization
173    
174      There are always ideas for new optimizations so as to speed up pattern
175      matching. Most of them try to save work by recognizing a non-match without
176      having to scan all the possibilities. These are some that I've recorded:
177    
178      * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
179        slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
180        OTOH, this is pathological - the user could easily fix it.
181    
182      * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
183        to have little effect, and maybe makes things worse.
184    
185      * "Ends with literal string" - note that a single character doesn't gain much
186        over the existing "required byte" (reqbyte) feature that just remembers one
187        byte.
188    
189      * These probably need to go in study():
190    
191        o Remember an initial string rather than just 1 char?
192    
193        o A required byte from alternatives - not just the last char, but an
194          earlier one if common to all alternatives.
195    
196        o Friedl contains other ideas.
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      * Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
209        character classes. For the moment, I've chosen not to support this for
210        backward compatibility, for speed, and because it would be messy to
211        implement.
212    
213      * A different approach to Unicode might be to use a typedef to do everything
214        in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
215        new typedef to distinguish data from bits of compiled pattern that are in
216        bytes, I think. There would need to be conversion functions in and out. I
217        don't think this is particularly trivial - and anyway, Unicode now has
218        characters that need more than 16 bits, so is this at all sensible?
219    
220      * There has been a request for direct support of 16-bit characters and
221        UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
222        is this worth it at all? One possible way of handling 16-bit characters
223        would be to "load" them in the same way that UTF-8 characters are loaded.
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    
316    . Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
317      "something" and the the #ifdef appears only in one place, in "something".
318    
319    . Support for (*MARK) and arguments for (*PRUNE) and friends.
320    
321    Philip Hazel
322    Email local part: ph10
323    Email domain: cam.ac.uk
324    Last updated: 10 March 2010

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