pcre/maint/README

MAINTENANCE README FOR PCRE2
============================

The files in the "maint" directory of the PCRE2 source contain data, scripts,
and programs that are used for the maintenance of PCRE2, but which do not form
part of the PCRE2 distribution tarballs. This document describes these files
and also contains some notes for maintainers. Its contents are:

  Files in the maint directory
  Updating to a new Unicode release
  Preparing for a PCRE2 release
  Making a PCRE2 release
  Long-term ideas (wish list)


Files in the maint directory
============================

GenerateUtt.py   A Python script to generate part of the pcre2_tables.c file
                 that contains Unicode script names in a long string with
                 offsets, which is tedious to maintain by hand.

ManyConfigTests  A shell script that runs "configure, make, test" a number of
                 times with different configuration settings.

MultiStage2.py   A Python script that generates the file pcre2_ucd.c from three
                 Unicode data tables, which are themselves downloaded from the
                 Unicode web site. Run this script in the "maint" directory.
                 The generated file contains the tables for a 2-stage lookup
                 of Unicode properties.

pcre2_chartables.c.non-standard
                 This is a set of character tables that came from a Windows
                 system. It has characters greater than 128 that are set as
                 spaces, amongst other things. I kept it so that it can be
                 used for testing from time to time.

README           This file.

Unicode.tables   The files in this directory (CaseFolding.txt, 
                 DerivedGeneralCategory.txt, GraphemeBreakProperty.txt,
                 Scripts.txt and UnicodeData.txt) were downloaded from the
                 Unicode web site. They contain information about Unicode
                 characters and scripts. 

ucptest.c        A short C program for testing the Unicode property macros
                 that do lookups in the pcre2_ucd.c data, mainly useful after
                 rebuilding the Unicode property table. Compile and run this in
                 the "maint" directory (see comments at its head).

ucptestdata      A directory containing two files, testinput1 and testoutput1,
                 to use in conjunction with the ucptest program.

utf8.c           A short, freestanding C program for converting a Unicode code
                 point into a sequence of bytes in the UTF-8 encoding, and vice
                 versa. If its argument is a hex number such as 0x1234, it
                 outputs a list of the equivalent UTF-8 bytes. If its argument
                 is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
                 treats them as a UTF-8 character and outputs the equivalent
                 code point in hex.


Updating to a new Unicode release
=================================

When there is a new release of Unicode, the files in Unicode.tables must be
refreshed from the web site. If the new version of Unicode adds new character
scripts, the source file pacr2_ucp.h and both the MultiStage2.py and the
GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
can be run to generate a new version of pcre2_ucd.c, and GenerateUtt.py can be
run to generate the tricky tables for inclusion in pcre2_tables.c.

If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
the cause is usually a missing (or misspelt) name in the list of scripts. I
couldn't find a straightforward list of scripts on the Unicode site, but
there's a useful Wikipedia page that list them, and notes the Unicode version
in which they were introduced:

http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts

The ucptest program can be compiled and used to check that the new tables in
pcre2_ucd.c work properly, using the data files in ucptestdata to check a
number of test characters. The source file ucptest.c must be updated whenever
new Unicode script names are added.

Note also that both the pcre2syntax.3 and pcre2pattern.3 man pages contain
lists of Unicode script names.


Preparing for a PCRE release
============================

This section contains a checklist of things that I consult before building a
distribution for a new release.

. Ensure that the version number and version date are correct in configure.ac.

. Update the library version numbers in configure.ac according to the rules 
  given below.

. If new build options have been added, ensure that they are added to the CMake
  files as well as to the autoconf files. The relevant files are CMakeLists.txt
  and config-cmake.h.in. After making a release tarball, test it out with CMake 
  if there have been changes here.  

. Run ./autogen.sh to ensure everything is up-to-date.

. Compile and test with many different config options, and combinations of
  options. Also, test with valgrind by running "RunTest valgrind" and
  "RunGrepTest valgrind" (which takes quite a long time). The script
  maint/ManyConfigTests now encapsulates this testing. It runs tests with
  different configurations, and it also runs some of them with valgrind, all of
  which can take quite some time.

. Run perltest.sh on the test data for tests 1 and 4. The output should match 
  the PCRE2 test output, apart from the version identification at the start of
  each test. The other tests are not Perl-compatible (they use various
  PCRE2-specific features or options).

. It is possible to test with the emulated memmove() function by undefining
  HAVE_MEMMOVE and HAVE_BCOPY in config.h, though I do not do this often. You
  may see a number of "pcre2_memmove defined but not used" warnings for the
  modules in which there is no call to memmove(). These can be ignored.

. Documentation: check AUTHORS, ChangeLog (check version and date), LICENCE, 
  NEWS (check version and date), NON-AUTOTOOLS-BUILD, and README. Many of these
  won't need changing, but over the long term things do change.

. I used to test new releases myself on a number of different operating
  systems, using different compilers as well. For example, on Solaris it is
  helpful to test using Sun's cc compiler as a change from gcc. Adding
  -xarch=v9 to the cc options does a 64-bit test, but it also needs -S 64 for
  pcretest to increase the stack size for test 2. Since I retired I can no
  longer do this, but instead I rely on putting out release candidates for
  folks on the pcre-dev list to test.
  
. The buildbots at http://buildfarm.opencsw.org/ do some automated testing
  of PCRE2 and should be checked before putting out a release. 
  

Updating version info for libtool
=================================

This set of rules for updating library version information came from a web page 
whose URL I have forgotten. The version information consists of three parts:
(current, revision, age).

1. Start with version information of 0:0:0 for each libtool library.

2. Update the version information only immediately before a public release of
   your software. More frequent updates are unnecessary, and only guarantee
   that the current interface number gets larger faster.

3. If the library source code has changed at all since the last update, then
   increment revision; c:r:a becomes c:r+1:a.

4. If any interfaces have been added, removed, or changed since the last
   update, increment current, and set revision to 0.

5. If any interfaces have been added since the last public release, then
   increment age.

6. If any interfaces have been removed or changed since the last public
   release, then set age to 0.

The following explanation may help in understanding the above rules a bit
better. Consider that there are three possible kinds of reaction from users to
changes in a shared library:

1. Programs using the previous version may use the new version as a drop-in
   replacement, and programs using the new version can also work with the
   previous one. In other words, no recompiling nor relinking is needed. In
   this case, increment revision only, don't touch current or age.

2. Programs using the previous version may use the new version as a drop-in
   replacement, but programs using the new version may use APIs not present in
   the previous one. In other words, a program linking against the new version
   may fail if linked against the old version at run time. In this case, set
   revision to 0, increment current and age.

3. Programs may need to be changed, recompiled, relinked in order to use the
   new version. Increment current, set revision and age to 0.


Making a PCRE2 release
======================

Run PrepareRelease and commit the files that it changes (by removing trailing
spaces). The first thing this script does is to run CheckMan on the man pages;
if it finds any markup errors, it reports them and then aborts.

Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
and the zipball. Double-check with "svn status", then create an SVN tagged
copy:

  svn copy svn://vcs.exim.org/pcre2/code/trunk \
           svn://vcs.exim.org/pcre2/code/tags/pcre-8.xx

When the new release is out, don't forget to tell webmaster@pcre.org and the
mailing list. Also, update the list of version numbers in Bugzilla (edit
products).


Future ideas (wish list)
========================

This section records a list of ideas so that they do not get forgotten. They
vary enormously in their usefulness and potential for implementation. Some are
very sensible; some are rather wacky. Some have been on this list for years;
others are relatively new.

. Optimization

  There are always ideas for new optimizations so as to speed up pattern
  matching. Most of them try to save work by recognizing a non-match without
  having to scan all the possibilities. These are some that I've recorded:

  * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
    slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
    OTOH, this is pathological - the user could easily fix it.

  * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
    to have little effect, and maybe makes things worse.

  * "Ends with literal string" - note that a single character doesn't gain much
    over the existing "required code unit" feature that just remembers one code
    unit.

  * Remember an initial string rather than just 1 code unit?

  * A required code unit from alternatives - not just the last unit, but an
    earlier one if common to all alternatives.

  o Friedl contains other ideas.

  * The code does not set initial code unit flags for Unicode property types
    such as \p; I don't know how much benefit there would be for, for example,
    setting the bits for 0-9 and all values >= xC0 (in 8-bit mode) when a
    pattern starts with \p{N}.

  * There is scope for more "auto-possessifying" in connection with \p and \P.

. If Perl gets to a consistent state over the settings of capturing sub-
  patterns inside repeats, see if we can match it. One example of the
  difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
  leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
  because I think it needs much more state to be remembered.

. Perl 6 will be a revolution. Is it a revolution too far for PCRE?

. Line endings:

  * Option to use NUL as a line terminator in subject strings. This could now
    be done relatively easily since the extension to support LF, CR, and CRLF.
    If it is done, a suitable option for pcre2grep is also required.

. Catch SIGSEGV for stack overflows?

. A feature to suspend a match via a callout was once requested.

. Option to convert results into character offsets and character lengths.

. Option for pcre2grep to scan only the start of a file. I am not keen - this
  is the job of "head".

. A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
  preceded by a blank line, instead of adding it to every matched line, and (b)
  support --outputfile=name.

. Define a union for the results from pcre2_pattern_info().

. Provide a "random access to the subject" facility so that the way in which it
  is stored is independent of PCRE2. For efficiency, it probably isn't possible
  to switch this dynamically. It would have to be specified when PCRE2 was
  compiled. PCRE2 would then call a function every time it wanted a character.

. Wild thought: the ability to compile from PCRE2's internal code to a real 
  FSM and a very fast (third) matcher to process the result. There would be
  even more restrictions than for pcre2_dfa_exec(), however. This is not easy.
  This is probably obsolete now that we have the JIT support.

. pcre2grep: add -rs for a sorted recurse? Having to store file names and sort
  them will of course slow it down.

. Someone suggested --disable-callout to save code space when callouts are
  never wanted. This seems rather marginal.

. A user suggested a parameter to limit the length of string matched, for
  example if the parameter is N, the current match should fail if the matched
  substring exceeds N. This could apply to both match functions. The value
  could be a new field in the match context.

. Callouts with arguments: (?Cn:ARG) for instance.

. Write a function that generates random matching strings for a compiled 
  pattern.

. Pcre2grep: an option to specify the output line separator, either as a string
  or select from a fixed list. This is not dead easy, because at the moment it
  outputs whatever is in the input file.

. Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
  non-thread-safe patch showed that this can help performance for patterns
  where there are many alternatives. However, a simple thread-safe
  implementation that I tried made things worse in many simple cases, so this
  is not an obviously good thing.

. PCRE2 cannot at present distinguish between subpatterns with different names,
  but the same number (created by the use of ?|). In order to do so, a way of
  remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
  Now that (*MARK) has been implemented, it can perhaps be used as a way round
  this problem.

. Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
  "something" and the the #ifdef appears only in one place, in "something".

Philip Hazel
Email local part: ph10
Email domain: cam.ac.uk
Last updated: 25 October 2014