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)
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 PrepareRelease.
CheckMan
A Perl script to validate the syntax in PCRE2 man pages, used by
PrepareRelease.
CheckMan
A Perl script to clean up the nroff output in PCRE2 man pages, used by
PrepareRelease.
Detrail
A Perl script to remove trailing whitespace from PCRE2 files, used by
PrepareRelease.
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.c from
GenerateCommon.py and Unicode data files. The generated file contains tables
for looking up Unicode property names.
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.
PrepareRelease
A shell script to ensure that all auto-generated outputs are ready for
release.
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.
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.c )
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.c
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.c
./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 (PH) do before building 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 or new source files 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, test
it out with CMake if there have been changes here.
. Run ./autogen.sh to ensure everything is up-to-date.
. Run the script maint/ManyConfigTests. This compiles and runs the tests for
many different sets of configuration options, some with valgrind. It can take
quite a long time.
. Run tests in both 32-bit and 64-bit environments if possible. I can no longer
run 32-bit tests.
. Run tests with two or more different compilers (e.g. clang and gcc), and make
use of -fsanitize=address and friends where possible. For gcc,
-fsanitize=undefined -std=gnu99 picks up undefined behaviour at runtime. For
clang, -fsanitize=address,undefined,integer can be used but an exception is
needed to allow XCLASS with very large ranges in the 32-bit library so it
should be followed by -fno-sanitize=unsigned-shift-base, additionally
-fno-sanitize=unsigned-integer-overflow must be added when compiling with
JIT. Newer versions of clang also need -fno-sanitize=function, at least
until pcre2test stops using generic pointers on its callbacks. Another
useful clang option is -fsanitize=signed-integer-overflow but that should
be already included if using "integer".
. Do a test build using CMake. Remove src/config.h first, lest it override the
version that CMake creates. Also ensure there is no leftover CMakeCache.txt
in the directory you are testing in.
. Remove the CMake cache and then check that a CMake unity build works:
[c]cmake -DCMAKE_UNITY_BUILD=ON sets up a unity build.
. 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.
. 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.
. 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. For example, on Solaris it is helpful to test using Sun's cc
compiler as a change from gcc. Adding -m64 to the cc options does a 64-bit
build. Since I retired I can no longer do much of this. There are automated
tests under Ubuntu, Alpine, macOS and Windows that are now set up as GitHub
actions. Check that they are running clean.
. The buildbots at http://buildfarm.opencsw.org/ do some automated testing
of PCRE2 and should also be checked before putting out a release. (June 2024:
I am not sure these are currently working properly.)
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. 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. Otherwise it removes trailing spaces from
sources and refreshes the HTML documentation. Update the GitHub repository.
Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
and the zipball. I then sign these files. Double-check with "git status" that
the repository is fully up-to-date, then create a new tag and a release on
GitHub. Upload the tarballs, zipball, and the signatures as "assets" of the
GitHub release.
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.
. Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
"something" and the the #ifdef appears only in one place, in "something".
. 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
