kmx git

@node Package version management
@section Package version management

@c Copyright (C) 2007--2025 Free Software Foundation, Inc.

@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3 or
@c any later version published by the Free Software Foundation; with no
@c Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A
@c copy of the license is at <https://www.gnu.org/licenses/fdl-1.3.en.html>.

The goals of a package maintainer,
when dealing with the version number of a package, are:

@itemize
@item
Programs should identify themselves with that version number
when invoked as @command{@var{program} --version}.

@item
Every package tarball should contain the version number, in up to four ways:
@itemize
@item
The tarball name should be @code{@var{package}-@var{version}.tar.gz}.
@item
The tarball should unpack into a directory
named @code{@var{package}-@var{version}}.
@item
Programs built from that tarball should identify themselves
when invoked as @command{@var{program} --version}.
@item
Documentation (especially in PDF format) and man pages
may contain the version number, as an important bit of meta information.
@end itemize

@item
The package maintainer should be able to
easily set the version number before making a release,
and doing so should be quick.

@item
When a contributor is
building from the git repository (as opposed to a tarball),
the version number should, by default, reflect the git commit,
in order to avoid confusion w.r.t. official releases.
@end itemize

Here's how the GNU Build System and Gnulib achieve these goals.

@menu
* Setting the package version::
* Propagating the package version::
* Using the package version::
@end menu

@node Setting the package version
@subsection Setting the package version

@cindex @code{.tarball-version}
When the maintainer has decided about the version number
for the next build (and likely also the next tarball),
they implement that decision by storing this version number
in a file named @file{.tarball-version} at the top level of the package.
This is a simple one-line text file.

The maintainer can, alternatively, decide to
let the git version be the version number.
To implement this choice,
they remove the file @file{.tarball-version} at the top level of the package.

@mindex git-version-gen
The actual version number comes from an invocation of
the program @code{git-version-gen},
part of the Gnulib module @code{git-version-gen}.
It looks at the file @file{.tarball-version}, if that exists,
and at the current checkout, otherwise.

The file @file{.tarball-version} should not be put under version control.
Therefore you may want to list it
in the package's top-level @code{.gitignore} file.

But you need a @code{Makefile.am} rule that will
make sure that @file{.tarball-version} will exist in distribution tarballs:

@example
dist-hook: dist-tarball-version
.PHONY: dist-tarball-version
dist-tarball-version:
	echo '$(VERSION)' > $(distdir)/.tarball-version
@end example

Typically, the maintainer will set the version number in a clean directory
(i.e. after ``make distclean'').
@mindex gnumakefile
In order to adapt to alternative workflows,
the file @file{GNUmakefile}, part of the Gnulib module @code{gnumakefile},
contains a rule that will print a warning or possibly call @code{autoreconf}
if it finds that the version has changed but has not yet been propagated.
Reminder: Not every package supports @code{autoreconf}.

@node Propagating the package version
@subsection Propagating the package version

At the end of a @file{configure} run,
@code{config.status} is run,
that creates various files with embedded pieces of information.
It thus propagates the values of various variables
to various files in the build tree
(most notably, @code{Makefile}s and @code{config.h}).

One such propagated value is
the value of the Automake-defined variable @code{$(VERSION)}.
(There is also the Autoconf-defined variable @code{$(PACKAGE_VERSION)},
but nothing except Automake ought to use it.)

For @code{$(VERSION)} to have a sensible value,
a few lines are needed in @code{configure.ac}.

The recommended code pattern is
@example
AC_INIT([@var{package}], [package])
AC_CONFIG_SRCDIR([@var{unique-file-in-source-dir}])
AC_CONFIG_AUX_DIR([build-aux])
VERSION_NUMBER=`cd $srcdir \
                && build-aux/git-version-gen .tarball-version`
gl_INIT_PACKAGE_VERSION([$VERSION_NUMBER])
AM_INIT_AUTOMAKE([@var{options}])
@end example
@noindent
With this code pattern,
the contents of the file @file{.tarball-version} and the git status
are considered when @code{configure} is run.

Two older code patterns are deprecated, because they read
the contents of the file @file{.tarball-version} and the git status
when @code{autoconf} is run, not when @code{configure} is run.
These older code patterns thus require a longer turnaround cycle
when the maintainer has changed the version number.

The first such old code pattern
is to set the version number directly in @code{configure.ac}:
@example
AC_INIT([@var{package}, @var{version}])
AC_CONFIG_SRCDIR([@var{unique-file-in-source-dir}])
AC_CONFIG_AUX_DIR([build-aux])
AM_INIT_AUTOMAKE([@var{options}])
@end example

The second such old code pattern
is to invoke @code{git-version-gen} at @code{autoconf} time:
@example
AC_INIT([@var{package}],
        m4_esyscmd([build-aux/git-version-gen .tarball-version])])
AC_CONFIG_SRCDIR([@var{unique-file-in-source-dir}])
AC_CONFIG_AUX_DIR([build-aux])
AM_INIT_AUTOMAKE([@var{options}])
@end example

@mindex package-version
The macro @code{gl_INIT_PACKAGE_VERSION}
is defined in the Gnulib module @code{package-version}.

@node Using the package version
@subsection Using the package version during the build

@subsubheading The unoptimized way

Once propagated through @code{config.status},
the value of @code{$(VERSION)} can appear anywhere in built files.
For built files that are
distributed (that is, not erased by ``make distclean''),
it is important to add a dependency in the @code{Makefile.am},
so that the file gets rebuilt:
@example
@var{built-file}: $(top_builddir)/config.status
@end example

For files that are erased by ``make distclean'', this is not really necessary,
because
@itemize
@item
In the main workflow, where the developer
changes the version only between ``make distclean'' and ``./configure'',
the built files have been remade.
@item
Most @code{.o} files depend on @code{config.h},
which is rebuilt when @code{configure} runs.
@end itemize

Thus, only in packages that don't use Gnulib would a dependency such as
@example
hello-hello.$(OBJEXT): $(top_builddir)/config.status
@end example
@noindent
be needed.

@subsubheading The optimized way

Notice that
@code{config.status} usually changes much more often than the version number.
Therefore, for built files which depend
@emph{only} on @code{$(VERSION)} and not on other variables,
the following optimized technique can be used.

The technique consists of keeping a file named @code{$(top_srcdir)/.version},
which is a timestamp file.
Its modification time represents the last time
the value of @code{$(VERSION)} was changed.
Its contents is an undocumented implementation detail.

With such a file, the dependency in @code{Makefile.am} becomes:
@example
@var{built-file}: $(top_srcdir)/.version
@end example

In order to prepare for using @code{$(top_srcdir)/.version},
three modifications in the package are needed:
@itemize
@item
In the top-level @code{configure.ac} file,
add an invocation of the macro @code{gl_CONFIG_VERSION_STAMP},
near the end (before @code{AC_OUTPUT}).
This macro is defined in file @file{m4/version-stamp.m4},
part of the Gnulib module @code{version-stamp}.
@item
In the top-level @code{Makefile.am}, add:
@example
EXTRA_DIST += $(top_srcdir)/.version
BUILT_SOURCES += $(top_srcdir)/.version
@end example
@noindent
so that the file @code{.version} will be present in tarballs
and so that ``make maintainer-clean'' will erase it.
@item
Add @code{.version} to the package's top-level @code{.gitignore} file.
@end itemize
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