maint: autogenerate ChangeLog

Following the practice set by various other GNU projects, we start
to automatically generate the ChangeLog file from the git commit
messages.  This will avoid duplication (as the ChangeLog entries
were always inserted both in the git commit message and in the
version-controlled ChangeLog file), and potential problems with
spurious merge conflicts (which, although greatly mitigated by
Bruno Haible's `git-merge-changelog' helper program, have never
been completely solved).

* ChangeLog: Moved ...
* ChangeLog.11:... to this.
* Makefile.am (EXTRA_DIST): Add it.
(gitlog_to_changelog_command, gitlog_to_changelog_options): New
variables.
(ChangeLog, am--changelog-regen-hook): New targets.
* .gitignore: Add ChangeLog.

1 files changed, 38 insertions, 0 deletions

diff --git a/Makefile.am b/Makefile.am
index acb722838..ed01bbb00 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -42,6 +42,7 @@ EXTRA_DIST = \
   ChangeLog.03 \
   ChangeLog.04 \
   ChangeLog.09 \
+  ChangeLog.11 \
   bootstrap \
   $(AUTOMAKESOURCES)
 
@@ -108,6 +109,43 @@ INSTALL: lib/INSTALL
 ## to anybody else
 ##
 
+gitlog_to_changelog_command = $(PERL) $(srcdir)/lib/gitlog-to-changelog
+gitlog_to_changelog_options = --since='2011-12-28 00:00:00'
+
+# Automatic generation of the ChangeLog from git history.
+#
+# When executed from a git checkout, generate the ChangeLog from the git
+# history.  When executed from an extracted distribution tarball, just
+# copy the distributed ChangeLog in the build directory (and if this
+# fails, or if no distributed ChangeLog file is present, complain and
+# give an error).
+#
+# We need the apparently useless dependency from another .PHONY target
+# `am--changelog-regen-hook' to work around a bug of Solaris make, which
+# doesn't execute the recipe of a target named as an existing file, even
+# if such target is declared `.PHONY' (yikes!)
+#
+.PHONY: am--changelog-regen-hook
+am--changelog-regen-hook:
+ChangeLog: am--changelog-regen-hook
+	$(AM_V_GEN)set -e; set -u; \
+## The ChangeLog should be regenerated unconditionally when working from
+## checked-out sources; otherwise, if we're working from a distribution
+## tarball, we expect the ChangeLog to be distributed, so check that it
+## is indeed present in the source directory.
+	if test -d $(srcdir)/.git; then \
+	  rm -f $@-t \
+	    && $(gitlog_to_changelog_command) \
+	       $(gitlog_to_changelog_options) >$@-t \
+	    && chmod a-w $@-t \
+	    && mv -f $@-t $@ \
+	    || exit 1; \
+	elif test ! -f $(srcdir)/$@; then \
+	  echo "Source tree is not a git checkout, and no pre-existent" \
+	       "$@ file has been found there" >&2; \
+	  exit 1; \
+	fi
+
 # Ensure tests are world-executable
 dist-hook:
 	cd $(distdir)/tests && chmod a+rx *.test