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This file attempts to describe the rules to use when hacking Bison. Don't put this file into the distribution.

Everything related to the development of Bison is on Savannah: http://savannah.gnu.org/projects/bison/.

Administrivia

If you incorporate a change from somebody on the net:

First, if it is a large change, you must make sure they have signed the appropriate paperwork. Second, be sure to add their name and email address to THANKS.

If a change fixes a test, mention the test in the commit message.

Bug reports

If somebody reports a new bug, mention his name in the commit message and in the test case you write. Put him into THANKS.

The correct response to most actual bugs is to write a new test case which demonstrates the bug. Then fix the bug, re-run the test suite, and check everything in.

Hacking

Visible Changes

Which include serious bug fixes, must be mentioned in NEWS.

Translations

Only user visible strings are to be translated: error messages, bits of the .output file etc. This excludes impossible error messages (comparable to assert/abort), and all the --trace output which is meant for the maintainers only.

Syntax highlighting

It's quite nice to be in C++ mode when editing lalr1.cc for instance. However tools such as Emacs will be fooled by the fact that braces and parens do not nest, as in [[}]]. As a consequence you might be misguided by its visual pairing to parens. The m4-mode is safer. Unfortunately the m4-mode is also fooled by # which is sees as a comment, stops pairing with parens/brackets that are inside...

Coding Style

Do not add horizontal tab characters to any file in Bison's repository except where required. For example, do not use tabs to format C code. However, make files, ChangeLog, and some regular expressions require tabs. Also, test cases might need to contain tabs to check that Bison properly processes tabs in its input.

Prefer "res" as the name of the local variable that will be "return"ed by the function.

Bison

Follow the GNU Coding Standards.

Don't reinvent the wheel: we use gnulib, which features many components. Actually, Bison has legacy code that we should replace with gnulib modules (e.g., many ad hoc implementations of lists).

Skeletons

We try to use the "typical" coding style for each language.

CPP

We indent the CPP directives this way:

#if FOO
# if BAR
#  define BAZ
# endif
#endif

Don't indent with leading spaces in the skeletons (it's ok in the grammar files though, e.g., in %code {...} blocks).

On occasions, use cppi -c to see where we stand. We don't aim at full correctness: depending -d, some bits can be in the *.c file, or the *.h file within the double-inclusion cpp-guards. In that case, favor the case of the *.h file, but don't waste time on this.

Don't hesitate to leave a comment on the #endif (e.g., #endif /* FOO */), especially for long blocks.

There is no conistency on ! defined vs. !defined. The day gnulib decides, we'll follow them.

C/C++

Follow the GNU Coding Standards.

The glr.c skeleton was implemented with camlCase. We are migrating it to snake_case. Because we are standardizing the code, it is currently inconsistent.

Use YYFOO and yyfoo for entities that are exposed to the user. They are part of our contract with the users wrt backward compatibility.

Use YY_FOO and yy_foo for private matters. Users should not use them, we are free to change them without fear of backward compatibility issues.

Use *_t for types, especially for yy*_t in which case we shouldn't worry about the C standard introducing such a name.

C++

Follow the C++ Core Guidelines (http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines). The Google ones may be interesting too (https://google.github.io/styleguide/cppguide.html).

Our enumerators, such as the kinds (symbol and token kinds), should be lower case, but it was too late to follow that track for token kinds, and symbol kind enumerators are made to be consistent with them.

Use *_type for type aliases. Use foo_get() and foo_set(v) for accessors, or simply foo() and foo(v).

Use the yy prefix for private stuff, but there's no need for it in the public API. The yy prefix is already taken care of via the namespace.

Java

We follow https://www.oracle.com/technetwork/java/codeconventions-150003.pdf and https://google.github.io/styleguide/javaguide.html. Unfortunately at some point some GNU Coding Style was installed in Java, but it's an error. So we should for instance stop putting spaces in function calls. Because we are standardizing the code, it is currently inconsistent.

Use a 2-space indentation (Google) rather than 4 (Oracle).

Don't use the "yy" prefix for public members: "getExpectedTokens", not "yyexpectedTokens" or "yygetExpectedTokens".

Commit Messages

Imitate the style we use. Use git log to get sources of inspiration.

If the changes have a small impact on Bison's generated parser, embed these changes in the commit itself. If the impact is large, first push all the changes except those about src/parse-gram.[ch], and then another commit named "regen" which is only about them.

Debugging

Bison supports tracing of its various steps, via the --trace option. Since it is not meant for the end user, it is not displayed by bison --help, nor is it documented in the manual. Instead, run bison --trace=help.

Documentation

Use @option for options and options with their argument if they have no space (e.g., @option{-Dfoo=bar}). However, use @samp elsewhere (e.g., @samp{-I foo}).

Working from the Repository

These notes intend to help people working on the checked-out sources. These requirements do not apply when building from a distribution tarball.

Requirements

We've opted to keep only the highest-level sources in the repository. This eases our maintenance burden, (fewer merges etc.), but imposes more requirements on anyone wishing to build from the just-checked-out sources. For example, you have to use the latest stable versions of the maintainer tools we depend upon, including:

Valgrind http://valgrind.org/ is also highly recommended, if it supports your architecture.

If you're using a GNU/Linux distribution, the easiest way to install the above packages depends on your system. The following shell command should work for Debian-based systems such as Ubuntu:

sudo apt-get install \
  autoconf automake autopoint flex graphviz help2man texinfo valgrind

Bison is written using Bison grammars, so there are bootstrapping issues. The bootstrap script attempts to discover when the C code generated from the grammars is out of date, and to bootstrap with an out-of-date version of the C code, but the process is not foolproof. Also, you may run into similar problems yourself if you modify Bison.

Only building the initial full source tree will be a bit painful. Later, after synchronizing from the repository a plain 'make' should be sufficient. Note, however, that when gnulib is updated, running './bootstrap' again might be needed.

First checkout

Obviously, if you are reading these notes, you did manage to check out this package from the repository. For the record, you will find all the relevant information on http://savannah.gnu.org/git/?group=bison.

Bison uses Git submodules: subscriptions to other Git repositories. In particular it uses gnulib, the GNU portability library. To ask Git to perform the first checkout of the submodules, run

$ git submodule update --init

The next step is to get other files needed to build, which are extracted from other source packages:

$ ./bootstrap

Bootstrapping updates the submodules to the versions registered in the top-level directory. To change gnulib, first check out the version you want in gnulib, then commit this change in Bison's repository, and finally run bootstrap.

If it fails with missing symbols (e.g., error: possibly undefined macro: AC_PROG_GNU_M4), you are likely to have forgotten the submodule initialization part. To recover from it, run git reset --hard HEAD, and restart with the submodule initialization. Otherwise, there you are! Just

$ ./configure
$ make
$ make check

At this point, there should be no difference between your local copy, and the master copy:

$ git diff

should output no difference.

Enjoy!

Updating

If you have git at version 1.8.2 or later, the command

$ git submodule update --recursive --remote

will be useful for updating to the latest version of all submodules.

Under earlier versions, use of submodules make things somewhat different because git does not yet support recursive operations: submodules must be taken care of explicitly.

Updating Bison

If you pull a newer version of a branch, say via git pull, you might import requests for updated submodules. A simple git diff will reveal if the current version of the submodule (i.e., the actual contents of the gnulib directory) and the current request from the subscriber (i.e., the reference of the version of gnulib that the Bison repository requests) differ. To upgrade the submodules (i.e., to check out the version that is actually requested by the subscriber, run git submodule update.

$ git pull
$ git submodule update

Updating a submodule

To update a submodule, say gnulib, do as follows:

Get the most recent version of the master branch from git.

$ cd gnulib
$ git fetch
$ git checkout -b master --track origin/master

Make sure Bison can live with that version of gnulib.

$ cd ..
$ ./bootstrap
$ make distcheck

Register your changes.

$ git commit ...

For a suggestion of what gnulib commit might be stable enough for a formal release, see the ChangeLog in the latest gnulib snapshot at http://erislabs.net/ianb/projects/gnulib/.

The Autoconf files we use are currently:

  • m4/m4.m4
  • lib/m4sugar/m4sugar.m4
  • lib/m4sugar/foreach.m4

These files don't change very often in Autoconf, so it should be relatively straight-forward to examine the differences in order to decide whether to update.

Troubleshooting

Bison is self-hosted: its parser is generated by Bison. We don't force ourselves to use the previous release of Bison, we use the current git master for several reasons:

  • dogfooding: let Bison be its first user
  • monitoring: seeing the diff on the generated parsers with git is very helpful, as it allows to see easily the impact of the changes on a real case parser.

If you are unlucky the generated files, src/parse-gram.[ch], may be older than their source, src/parse-gram.y. And your current version of Bison might not be able to grok it. In that case, first refresh the generated files:

$ touch src/parse-gram.[ch]

Then proceed.

In case you wrecked your current copy of the parser, get back the previous version, compile bison, then force it to recreate the files:

$ git checkout HEAD^ src/parse-gram.[ch]
$ make -C _build
$ touch src/parse-gram.y
$ make -C _build

Test Suite

make check

Consume without moderation. It is composed of two kinds of tests: the examples, and the main test suite.

The Examples

In examples/, there is a number of ready-to-use examples (see examples/README.md). These examples have small test suites run by make check. The test results are in local *.log files (e.g., $build/examples/c/calc/calc.log).

The Main Test Suite

The main test suite, in tests/, is written on top of GNU Autotest, which is part of Autoconf. Run info autoconf 'Using Autotest' to read the documentation, not only about how to write tests, but also where are the logs, how to read them etc.

The main test suite generates a log for each test (e.g., $build/tests/testsuite.dir/004/testsuite.log for test #4), and a main log file in $build/tests/testsuite.log. The latter is meant for end users: it contains lots of details that should help diagnosing issues, including build issues. The per-test logs are more convenient when working locally.

TESTSUITEFLAGS

To run just the main test suite, run make check-local.

The default is for make check-local to run all tests sequentially. This can be very time consuming when checking repeatedly or on slower setups. This can be sped up in two ways:

Using -j, in a make-like fashion, for example:

$ make check-local TESTSUITEFLAGS='-j8'

Actually, when using GNU Make, TESTSUITEFLAGS defaults to the -jN passed to it, so you may simply run

$ make check-local -j8

Running only the tests of a certain category, as specified in the AT files with AT_KEYWORDS([[category]]). Categories include:

  • c++, for c++ parsers
  • deprec, for tests concerning deprecated constructs.
  • glr, for glr parsers
  • java, for java parsers
  • report, for automaton dumps

To get a list of all the tests (and their keywords for -k), run

$ ./tests/testsuite -l

To run a specific set of tests, use -k (for "keyword"). For example:

$ make check-local TESTSUITEFLAGS='-k c++'

Both can be combined.

$ make check-local TESTSUITEFLAGS='-j8 -k c++'

To rerun the tests that failed:

$ make recheck -j5

Updating the Expectations

Sometimes some changes have a large impact on the test suite (e.g., when we added the [-Wother] part to all the warnings). Part of the update can be done with a crude tool: build-aux/update-test.

Once you ran the test suite, and therefore have many testsuite.log files, run, from the source tree:

$ ./build-aux/update-test $build/tests/testsuite.dir/*/testsuite.log

where $build would be your build tree. This will hopefully update most tests. Re-run the test suite. It might be interesting to run update-test again, since some early failures may stop latter tests from being run. Yet at some point, you'll have to fix remaining issues by hand...

Running Java parsers

Use the javaexec.sh script. For instance to run the parser of test case 504:

$ sh ./_build/javaexec.sh -cp ./_build/tests/testsuite.dir/504 Calc

make maintainer-check-valgrind

This target uses valgrind both to check bison, and the generated parsers.

This is not mature on Mac OS X. First, Valgrind does support the way bison calls m4, so Valgrind cannot be used to check bison on Mac OS X.

Second, there are many errors that come from the platform itself, not from bison. build-aux/darwin11.4.0.valgrind addresses some of them.

Third, valgrind issues warnings such as:

--99312:0:syswrap- WARNING: Ignoring sigreturn( ..., UC_RESET_ALT_STACK );

which cause the test to fail uselessly. It is hard to ignore these errors with a major overhaul of the way instrumentation is performed in the test suite. So currently, do not try to run valgrind on Mac OS X.

Release checks

Try to run the test suite with more severe conditions before a release:

  • Configure the package with --enable-gcc-warnings, so that one checks that

    1. Bison compiles cleanly, 2. the parsers it produces compile cleanly too.

  • Maybe build with -DGNULIB_POSIXCHECK, which suggests gnulib modules that can fix portability issues. See if you really want to pay attention to its warnings; there's no need to obey blindly to it (http://lists.gnu.org/archive/html/bison-patches/2012-05/msg00057.html).

  • Check with make syntax-check if there are issues diagnosed by gnulib.

  • run make maintainer-check which:

    • runs valgrind -q bison to run Bison under Valgrind.
    • runs the parsers under Valgrind.
    • runs the test suite with G++ as C compiler...

  • run make maintainer-check-push, which runs make maintainer-check while activating the push implementation and its pull interface wrappers in many test cases that were originally written to exercise only the pull implementation. This makes certain the push implementation can perform every task the pull implementation can.

  • run make maintainer-check-xml, which runs make maintainer-check while checking Bison's XML automaton report for every working grammar passed to Bison in the test suite. The check just diffs the output of Bison's included XSLT style sheets with the output of --report=all and --graph.

  • running make maintainer-check-release takes care of running maintainer-check, maintainer-check-push and maintainer-check-xml.

  • Change tests/atlocal/CFLAGS to add your preferred options.

  • Test with a very recent version of GCC for both C and C++. Testing with older versions that are still in use is nice too.

gnulib

To run tests on gnulib components (e.g., on bitset):

cd gnulib
./gnulib-tool --test bitset-tests

possibly within a specified environment:

CC='gcc-mp-8 -fsanitize=undefined' ./gnulib-tool --test bitset-tests

To be able to run the tests several times, and to use symlinks instead of copies so that one can update the origin gnulib directory and immediately re-run the tests, run:

./gnulib-tool --symlink --create-test --dir=/tmp/gnutest bitset-tests
cd /tmp/gnutest
./configure -C CC='gcc-mp-8 -fsanitize=undefined' CFLAGS='-ggdb'
make check

Release Procedure

See README-release.