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
  Updating version info for libtool
  Long-term ideas (wish list)

For a description of the way PCRE2 works, see the file called HACKING in the
top directory.


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

132html
  A Perl script to convert man pages to HTML (.1 and .3 files "two" HTML),
  used by UpdateAlways.

CheckMan
  A Perl script to validate the syntax in PCRE2 man pages, used by
  UpdateAlways.

CleanTxt
  A Perl script to clean up the nroff output in PCRE2 man pages, used by
  UpdateAlways.

Detrail
  A Perl script to remove trailing whitespace from PCRE2 files, used by
  UpdateAlways.

GenerateCommon.py
  A Python module containing data and functions that are used by the other
  Generate scripts.

GenerateTest.py
  A Python script that generates input and expected output test data for tests
  26 or 27, which tests certain aspects of Unicode property support.

GenerateUcd.py
  A Python script that generates the file pcre2_ucd.c from GenerateCommon.py
  and Unicode data files, which are themselves downloaded from the Unicode web
  site. The generated file contains the tables for a 2-stage lookup of Unicode
  properties, along with some auxiliary tables. The script starts with a long
  comment that gives details of the tables it constructs.

GenerateUcpHeader.py
  A Python script that generates the file pcre2_ucp.h from GenerateCommon.py
  and Unicode data files. The generated file defines constants for various
  Unicode property values.

GenerateUcpTables.py
  A Python script that generates the file pcre2_ucptables_inc.h from
  GenerateCommon.py and Unicode data files. The generated file contains tables
  for looking up Unicode property names.

FilterCoverage.py
  A small helper used by the RunCoverage script.

LintMan
  A Perl script to check and update magic numbers in the documentation that
  correspond to configurable settings in the codebase.

manifest-*
  Data files used to verify the contents of the distribution tarball and
  `make install` file lists.

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

UpdateAlways
  A shell script to ensure that all auto-generated outputs are ready for
  release.

  It should be run often (by CI on each commit) to ensure that the repository
  is in a clean and consistent state.

UpdateDates.py
UpdateRelease.py
  Python scripts to be run less frequently than UpdateAlways. These should only
  be needed immediately before a release, when finalising the repository.
  UpdateDates.py checks in the last-updated times on documentation pages.
  UpdateRelease.py is needed after any change to the version number in
  configure.ac.

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.

RunCoverage
  A script used to generate the coverage report using Clang. It is called by
  the GitHub CI actions, and can also be run by a developer locally.

RunManifestTest
RunManifestTest.ps1
  Scripts to generate and verify a list of files against an expected 'manifest'
  detailing what the directory should contain.

Unicode.tables
  The files in this directory were downloaded from the Unicode web site. They
  contain information about Unicode characters and scripts, and are used by the
  Generate scripts. There is also UnicodeData.txt, which is no longer used by
  any script, because it is useful occasionally for manually looking up the
  details of certain characters. However, note that character names in this
  file such as "Arabic sign sanah" do NOT mean that the character is in a
  particular script (in this case, Arabic). Scripts.txt and
  ScriptExtensions.txt are where to look for script information.

ucptest.c
  A program for testing the Unicode property macros that do lookups in the
  pcre2_ucd.c data, mainly useful after rebuilding the Unicode property tables.
  Compile and run this in the "maint" directory (see comments at its head).
  This program can also be used to find characters with specific properties and
  to list which properties are supported.

ucptestdata
  A directory containing four files, testinput{1,2} and testoutput{1,2}, for
  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 a sequence of concatenated UTF-8 bytes (e.g. 12e188b4) it
  treats them as a UTF-8 string and outputs the equivalent code points in hex.
  See comments at its head for details.


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

When there is a new release of Unicode, the files in Unicode.tables must be
refreshed from the Unicode web site. Once that is done, the four Python scripts
that generate files from the Unicode data can be run from within the "maint"
directory. Note that the format used for those files is not stable, and
therefore changes to the scripts might be needed to support new versions.

Note: Previously, it was necessary to update lists of scripts and their
abbreviations by hand before running the Python scripts. This is no longer
necessary because the scripts have been upgraded to extract this information
themselves. Also, there used to be explicit lists of scripts in two of the man
pages. This is no longer the case; the pcre2test program can now output a list
of supported scripts, and the command to do so is part of the documentation.

You can give an output file name as an argument to the following scripts, but
by default:

GenerateUcd.py        creates pcre2_ucd.c            )
GenerateUcpHeader.py  creates pcre2_ucp.h            ) in the current directory
GenerateUcpTables.py  creates pcre2_ucptables_inc.h  )

These files can be compared against the existing versions in the src directory
to check on any changes before replacing the old files, but you can also
generate directly into the final location by running:

./GenerateUcd.py       ../src/pcre2_ucd.c
./GenerateUcpHeader.py ../src/pcre2_ucp.h
./GenerateUcpTables.py ../src/pcre2_ucptables_inc.h

Once the .c and .h files are in the ../src directory, the ucptest program can
be compiled and used to check that the new tables work properly. The data files
in ucptestdata are set up to check a number of test characters. See the
comments at the start of ucptest.c. Depending of the type of changes, adding
tests for new scripts, properties or characters to the files in ucptestdata
is recommended. Make sure to regenerate and validate the output files after.

Finally, you should run the GenerateTest.py script to regenerate new versions
of the input and expected output from a series of Unicode property tests that
are automatically generated from the Unicode data files. By default, the files
are written to testinput and testoutput in the current directory, but they
should be moved to replace the files inside the main testdata directory and
that are being used for tests 27 or 26.

In summary:

```
./GenerateUcd.py       ../src/pcre2_ucd.c
./GenerateUcpHeader.py ../src/pcre2_ucp.h
./GenerateUcpTables.py ../src/pcre2_ucptables_inc.h
./GenerateTest.py
mv testinput ../testdata/testinput27
mv testoutput ../testdata/testoutput27

...compile ucptest.c
for i in 1 2; do
  ./ucptest < ucptestdata/testinput$i > testoutput$i
  diff -U3 testoutput$i ucptestdata/testoutput$i
done
```


Preparing for a PCRE2 release
=============================

This section contains a checklist of things that I (NCW) do before building a
new release.

* First of all, make sure that the master branch is in good condition.

  - Basically, test it. The CI jobs should all be passing. This ensures that
    pcre2tests are passing, that the build is warning-free, and that all our
    platforms are running correctly. The CI jobs should be running the Perl
    tests (which assert that `testdata/testinput1` tests give the same results
    using Perl's regex engine). The ManyConfigTests exercise a variety of
    build options and combinations. The Autoconf and CMake builds must pass.

  - If new build options have been added, ensure that they are added to the
    CMake files as well as to the Autoconf files.

  - 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. Sometimes there are other differences in test 4 if PCRE2 and Perl
    are using different Unicode releases. The other tests are not
    Perl-compatible (they use various PCRE2-specific features or options). The
    maint/RunPerlTest shell script can be used to do this testing in Unix-like
    environment.

  - Check the external testing tools. CodeQL & Clang Static Analyzer report
    their results to the GitHub "Security" dashboard. Coverity has its own
    external dashboard, as does OSS-Fuzz. Since we have these tools, we should
    at least confirm they haven't flagged anything.

  - Documentation: check the documentation is ready; and LICENCE,
    NON-AUTOTOOLS-BUILD, and README. Many of these won't need changing, but over
    the long term things do change.

* Ensure the AUTHORS file is up-to-date with any new contributors since the
  last release. I use this simple command:

  ```sh
  git log $GIT_TAG..HEAD --format='RealAuthor: %aN <%aE>%n%w(80,4,4)%b' | \
    grep -E '^RealAuthor: .*|Co-authored-by:' | \
    sed -E -e 's/RealAuthor: |.*Co-authored-by:\s*//' | \
    sort -u
  ```

* Ensure the ChangeLog and NEWS files are updated with everything that you want
  to announce in the new release.

  This command helps dump the Git commits:

  ```sh
  git log --reverse -p -U10 --invert-grep --grep='#noupdate' $GIT_TAG..HEAD \
    -- ':!doc/*.txt' ':!doc/html'
  ```

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

* Add the new library version to the src/libpcre2-*.sym files (even if no new
  symbols have been added since the last release).

* Push all these changes to master.

* Take a branch off master, named "release/pcre2-10.XX-RC1" or
  "release/pcre2-10.XX".

  All releases should come from master. The final release isn't branched off
  from the RC branch; the RC branch is a "throwaway" release which can be pruned
  from the linear history of the trunk of PCRE2's tree.

* In the new branch, remove the "-DEV" prefix from the version number and set
  the release date in configure.ac. Update the release date in the ChangeLog and
  NEWS files.

  ```
  vim configure.ac
  vim NEWS
  vim ChangeLog
  git add -u configure.ac NEWS ChangeLog
  git commit -m"Update version number and release date"
  ```

* Perform updates of the automatically-generated files.

  ```
  ./autogen.sh && ./configure
  rm src/config.h.generic src/pcre2.h.generic
  make src/config.h.generic src/pcre2.h.generic
  git clean -idx .
  git add -u src/config.h.generic src/pcre2.h.generic
  git commit -m"Automatic update of .generic files"

  maint/UpdateRelease.py
  maint/UpdateDates.py
  maint/UpdateAlways
  git add -u
  git commit -m"Automatic update of doc files #noupdate"
  ```

* Commit the Autoconf files to the branch. This is required so that users can
  check out the Git tag, and receive the same contents as the tarball users.

  ```
  ./autogen.sh
  git add -f Makefile.in aclocal.m4 ar-lib compile config.guess config.sub \
    configure depcomp install-sh ltmain.sh m4/libtool.m4 m4/ltoptions.m4 \
    m4/ltsugar.m4 m4/ltversion.m4 m4/lt~obsolete.m4 missing src/config.h.in \
    test-driver
  git commit -m"Commit autogen.sh output"
  ```

* Now, wait for the CI job to build the tarball. We can't do this locally: we
  want to be releasing a tarball which is signed by GitHub. The GitHub signature
  says, "Yes, the developer did not tamper with this tarball, we certify that it
  was derived solely from the contents of the Git repository at this commit
  hash".

* Create the tag locally. We can't do this via the GitHub UI: it has no way to
  create signed tags (since my GPG key lives on a Yubikey).

  ```
  git config user.signingkey 'FB63B406!'
  git tag -s pcre2-10.XX -m"Release 10.XX"
  git tag -v pcre2-10.XX
  ```

* Download the tarball from the CI artifacts. Sign these using the GPG key.

  ```
  KEYID=FB63B406
  for i in pcre2-10.XX.{zip,tar.gz,tar.bz2}; do
    gpg --output $i.sig --detach-sig --default-key $KEYID $i
    gpg --verify $i.sig
  done
  ```

* In the GitHub UI, create a "release" from the tag (which must have been
  already pushed). Add the tarballs and GPG signatures.

* Announce the release on the mailing list.

* Bump the version number on master to the next release, plus -DEV.

* After issuing a final release, merge the release tag back to master with:

  ```
  git merge -s ours release/pcre2-10.XX
  ```

  Do not do this for -RC releases, which are not included in the linear history
  of the PCRE2 development trunk.

  We want users with forks of PCRE2 to be able to update from release to the
  next by simply doing a `git merge` in their fork. If the release tag is not
  merged back to master, then users will see unnecessary Git conflicts when
  trying to fast-forward from one release to the next.


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.


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 many
years.

. 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.

  * 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}.

. Perl and PCRE2 sometimes differ in the settings of capturing subpatterns
  inside repeats. One example of the difference is the matching of
  /(main(O)?)+/ against mainOmain, where PCRE2 leaves $2 set. In Perl, it's
  unset. Changing this in PCRE2 will be very hard because I think it needs much
  more state to be remembered.

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

. An option to convert results into character offsets and character lengths.

. 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.

. 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. Compare the offset_limit feature,
  which limits where a match must start.

. 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 straightforward, because at the
  moment it outputs whatever is in the input file.

. Improve the code for duplicate checking in pcre2_dfa_match(). 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. (*MARK) can
  perhaps be used as a way round this problem. However, note that Perl does not
  distinguish: like PCRE2, a name is just an alias for a number in Perl.

. Implement something like (?(R2+)... to check outer recursions.

. If Perl ever supports the POSIX notation [[.something.]] PCRE2 should try
  to follow.

. A user wanted a way of ignoring all Unicode "mark" characters so that, for
  example "a" followed by an accent would, together, match "a". This can only
  be done clumsily at present by using a lookahead such as /(?=a)\X/, which
  works for "combining" characters.

. Perl supports [\N{x}-\N{y}] as a Unicode range, even in EBCDIC. PCRE2
  supports \N{U+dd..} everywhere, but not in EBCDIC.

. Unicode stuff from Perl:

    \b{gcb} or \b{g}    grapheme cluster boundary
    \b{sb}              sentence boundary
    \b{wb}              word boundary

  See Unicode TR 29. The last two are very much aimed at natural language.

. Allow a callout to specify a number of characters to skip. This can be done
  compatibly via an extra callout field.

. Allow callouts to return *PRUNE, *COMMIT, *THEN, *SKIP, with and without
  continuing (that is, with and without an implied *FAIL). A new option,
  PCRE2_CALLOUT_EXTENDED say, would be needed. This is unlikely ever to be
  implemented by JIT, so this could be an option for pcre2_match().

. A limit on substitutions: a user suggested somehow finding a way of making
  match_limit apply to the whole operation instead of each match separately.

. Some #defines could be replaced with enums to improve robustness.

. There was a request for an option for pcre2_match() to return the longest
  match. This would mean searching for all possible matches, of course.

. A neater way of handling recursion file names in pcre2grep, e.g. a single
  buffer that can grow. See also GitHub issue #2 (recursion looping via
  symlinks).

. A user suggested that before/after parameters in pcre2grep could have
  negative values, to list lines near to the matched line, but not necessarily
  the line itself. For example, --before-context=-1 would list the line *after*
  each matched line, without showing the matched line. The problem here is what
  to do with matches that are close together. Maybe a simpler way would be a
  flag to disable showing matched lines, only valid with either -A or -B?

. There was a suggestion for a pcre2grep colour default, or possibly a more
  general PCRE2GREP_OPT, but only for some options - not file names or patterns.

. Breaking loops that match an empty string: perhaps find a way of continuing
  if *something* has changed, but this might mean remembering additional data.
  "Something" could be a capture value, but then a list of previous values
  would be needed to avoid a cycle of changes.

. If a function could be written to find 3-character (or other length) fixed
  strings, at least one of which must be present for a match, efficient
  pre-searching of large datasets could be implemented.

. If pcre2grep had --first-line (match only in the first line) it could be
  efficiently used to find files "starting with xxx". What about --last-line?
  There was also the suggestion of an option for pcre2grep to scan only the
  start of a file. I am not keen - this is the job of "head".

. A user requested a means of determining whether a failed match was failed by
  the start-of-match optimizations, or by running the match engine. Easy enough
  to define a bit in the match data, but all three matchers would need work.

. Would inlining "simple" recursions provide a useful performance boost for the
  interpreters? JIT already does some of this, but it may not be worth it for
  the interpreters.

. Redesign handling of class/nclass/xclass because the compile code logic is
  currently very contorted and obscure. Also there was a request for a way of
  re-defining \w (and therefore \W, \b, and \B). An in-pattern sequence such as
  (?w=[...]) was suggested. Easiest way would be simply to inline the class,
  with lookarounds for \b and \B. Ideally the setting should last till the end
  of the group, which means remembering all previous settings; maybe a fixed
  amount of stack would do - how deep would anyone want to nest these things?

. A user suggested something like --with-build-info to set a build information
  string that could be retrieved by pcre2_config(). However, there's no
  facility for a length limit in pcre2_config(), and what would be the
  encoding?

. Quantified groups with a fixed count currently operate by replicating the
  group in the compiled bytecode. This may not really matter in these days of
  gigabyte memory, but perhaps another implementation might be considered.
  Needs coordination between the interpreters and JIT.

. The POSIX interface is no longer POSIX compatible, because regoff_t is still
  defined as an int.

. The POSIX interface is not thread safe because it modifies a pcre2_match
  inside its regex_t while doing matching. A thread safe version that uses
  a thread local object has been proposed but it will require that the code
  requires at least C11 compatibility.

. See also any suggestions in the GitHub issues.

Philip Hazel
Email local part: Philip.Hazel
Email domain: gmail.com
Last updated: 22 August 2024
