New module 'package-version'.

* m4/init-package-version.m4: New file, from GNU libunistring.
* modules/package-version: New file.
* modules/git-version-gen (Depends-on): Add it.

ChangeLog

@@ -1,3 +1,10 @@
+2025-01-22  Bruno Haible  <bruno@clisp.org>
+
+	New module 'package-version'.
+	* m4/init-package-version.m4: New file, from GNU libunistring.
+	* modules/package-version: New file.
+	* modules/git-version-gen (Depends-on): Add it.
+
 2025-01-19  Bruno Haible  <bruno@clisp.org>
 
 	attribute: Add note about ongoing standardization of some attributes.

m4/init-package-version.m4

@@ -0,0 +1,124 @@
+# init-package-version.m4
+# serial 3
+dnl Copyright (C) 1992-2025 Free Software Foundation, Inc.
+dnl This file is free software, distributed under the terms of the GNU
+dnl General Public License.  As a special exception to the GNU General
+dnl Public License, this file may be distributed as part of a program
+dnl that contains a configuration script generated by Autoconf, under
+dnl the same distribution terms as the rest of that program.
+
+# Make it possible to pass version numbers extracted from a file in
+# $(srcdir) to autoconf.
+#
+# Autoconf insists on passing the package name and version number to
+# every generated .h file and every Makefile. This was a reasonable
+# design at times when a version number was changed only once a month.
+# Nowadays, people often assign a new version number once a week, or
+# even change it each time a 'git' commit is made. Regenerating all
+# the files that depend on configure.ac (aclocal.m4, configure,
+# config.status, config.h, all Makefiles) may take 15 minutes. These
+# delays can severely hamper development.
+#
+# An alternative is to store the version number in a file in $(srcdir)
+# that is separate from configure.ac. It can be a data file, a shell
+# script, a .m4 file, or other. The essential point is that the maintainer
+# is responsible for creating Makefile dependencies to this version file
+# for every file that needs to be rebuilt when the version changes. This
+# typically includes
+#   - distributable documentation files that carry the version number,
+# but does not include
+#   - aclocal.m4, configure, config.status, config.h, all Makefiles,
+#   - executables.
+#
+# autoconf and automake make it hard to follow this approach:
+#
+# - If AC_INIT is used with arguments, there is a chicken-and-egg problem:
+#   The arguments need to be read from a file in $(srcdir). The location
+#   of $(srcdir) is only determined by AC_CONFIG_SRCDIR. AC_CONFIG_SRCDIR
+#   can only appear after AC_INIT (otherwise aclocal gives an error:
+#   "error: m4_defn: undefined macro: _m4_divert_diversion").
+#   Furthermore, the arguments passed to AC_INIT must be literals; for
+#   example, the assignment to PACKAGE_VERSION looks like this:
+#     [PACKAGE_VERSION=']AC_PACKAGE_VERSION[']
+#
+# - If AC_INIT is used without arguments:
+#   Automake provides its own variables, PACKAGE and VERSION, and uses them
+#   instead of PACKAGE_NAME and PACKAGE_VERSION that come from Autoconf.
+#   - If AM_INIT_AUTOMAKE is used with two arguments, automake options
+#     like 'silent-rules' cannot be specified.
+#   - If AM_INIT_AUTOMAKE is used in its one-argument form or without
+#     arguments at all, it triggers an error
+#     "error: AC_INIT should be called with package and version arguments".
+#   - If AM_INIT_AUTOMAKE is used in its one-argument form or without
+#     arguments at all, and _AC_INIT_PACKAGE is used before it, with
+#     the package and version number from the file as arguments, we get
+#     a warning: "warning: AC_INIT: not a literal: $VERSION_NUMBER".
+#     The arguments passed to _AC_INIT_PACKAGE must be literals.
+#
+# With the macro defined in this file, the approach can be coded like this:
+#
+#   AC_INIT
+#   AC_CONFIG_SRCDIR(WITNESS)
+#   . $srcdir/../version.sh
+#   gl_INIT_PACKAGE(PACKAGE, $VERSION_NUMBER)
+#   AM_INIT_AUTOMAKE([OPTIONS])
+#
+# and after changing version.sh, the developer can directly configure and build:
+#
+#   make distclean
+#   ./configure
+#   make
+#
+# Some other packages use another approach:
+#
+#   AC_INIT(PACKAGE,
+#           m4_normalize(m4_esyscmd([. ./version.sh; echo $VERSION_NUMBER])))
+#   AC_CONFIG_SRCDIR(WITNESS)
+#   AM_INIT_AUTOMAKE([OPTIONS])
+#
+# but here, after changing version.sh, the developer must first regenerate the
+# configure file:
+#
+#   make distclean
+#   ./autogen.sh --skip-gnulib
+#   ./configure
+#   make
+#
+
+# gl_INIT_PACKAGE(PACKAGE-NAME, VERSION)
+# --------------------------------------
+# followed by an AM_INIT_AUTOMAKE invocation,
+# is like calling AM_INIT_AUTOMAKE(PACKAGE-NAME, VERSION)
+# except that it can use computed non-literal arguments.
+AC_DEFUN([gl_INIT_PACKAGE],
+[
+  AC_BEFORE([$0], [AM_INIT_AUTOMAKE])
+  dnl Redefine AM_INIT_AUTOMAKE.
+  m4_define([gl_AM_INIT_AUTOMAKE],
+    m4_bpatsubst(m4_dquote(
+        m4_bpatsubst(m4_dquote(
+            m4_bpatsubst(m4_dquote(
+                m4_defn([AM_INIT_AUTOMAKE])),
+              [AC_PACKAGE_NAME], [gl_INIT_DUMMY])),
+          [AC_PACKAGE_TARNAME], [gl_INIT_EMPTY])),
+      [AC_PACKAGE_VERSION], [gl_INIT_DUMMY])
+    [AC_SUBST([PACKAGE], [$1])
+     AC_SUBST([VERSION], [$2])
+    ])
+  m4_define([AM_INIT_AUTOMAKE],
+    m4_defn([gl_RPL_INIT_AUTOMAKE]))
+])
+m4_define([gl_INIT_EMPTY], [])
+dnl Automake 1.16.4 no longer accepts an empty value for gl_INIT_DUMMY.
+dnl But a macro that later expands to empty works.
+m4_define([gl_INIT_DUMMY], [gl_INIT_DUMMY2])
+m4_define([gl_INIT_DUMMY2], [])
+AC_DEFUN([gl_RPL_INIT_AUTOMAKE], [
+  m4_ifval([$2],
+    [m4_fatal([After gl_INIT_PACKAGE, the two-argument form of AM_INIT_AUTOMAKE cannot be used.])])
+  gl_AM_INIT_AUTOMAKE([$1 no-define])
+  m4_if(m4_index([ $1 ], [ no-define ]), [-1],
+    [AC_DEFINE_UNQUOTED(PACKAGE, "$PACKAGE", [Name of package])
+     AC_DEFINE_UNQUOTED(VERSION, "$VERSION", [Version number of package])
+    ])
+])

modules/git-version-gen

@@ -5,6 +5,7 @@ Files:
 build-aux/git-version-gen
 
 Depends-on:
+package-version
 
 configure.ac:
 

modules/package-version

@@ -0,0 +1,19 @@
+Description:
+Support for a computed version string.
+
+Files:
+m4/init-package-version.m4
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+
+Include:
+
+License:
+GPLed build tool
+
+Maintainer:
+Bruno Haible