From f78dde64c011f95274eee188a09495c0f67ed81c Mon Sep 17 00:00:00 2001
From: Nick Bowler <nbowler@draconx.ca>
Date: Tue, 23 Feb 2021 00:39:30 -0500
Subject: [PATCH] Generate ChangeLog from git at packaging time.

Import the gitlog-to-changelog script from gnulib and add rules to
generate an up-to-date changelog from the git history, if available,
when running 'make dist'.

The ChangeLog is otherwise taken from srcdir as usual, so that
modified versions can be prepared from a release tarball without
requiring the full git history.  In this scenario, the ChangeLog
would have to be manually edited.

In case the ChangeLog generation fails, a distcheck-hook is added
to hopefully catch issues before releasing tarballs with a broken
ChangeLog.
---
 .gitignore         |  1 +
 ChangeLog          |  1 +
 Makefile.am        | 33 +++++++++++++++++++++++++++++++++
 m4/gnulib-cache.m4 |  2 ++
 4 files changed, 37 insertions(+)
 create mode 100644 ChangeLog

diff --git a/.gitignore b/.gitignore
index 735368e..dafb638 100644
--- a/.gitignore
+++ b/.gitignore
@@ -15,6 +15,7 @@
 /configure
 /depcomp
 /exported.sh
+/gitlog-to-changelog
 /install-sh
 /lib
 /libtool
diff --git a/ChangeLog b/ChangeLog
new file mode 100644
index 0000000..4e0b7e7
--- /dev/null
+++ b/ChangeLog
@@ -0,0 +1 @@
+Stub changelog, see the git history for changes.
diff --git a/Makefile.am b/Makefile.am
index 01ff0a6..4bdc88c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -149,6 +149,39 @@ unfuck-distdir:
 	find '$(distdir)' -type f -exec chmod u+w {} +
 .PHONY: unfuck-distdir
 
+GITLOG_FLAGS = --format='%s%n%n%b%n'
+
+dist-hook: generate-changelog
+generate-changelog: unfuck-distdir
+	-: "$${GIT_DIR=$(top_srcdir)/.git}"; \
+	  export GIT_DIR; test -d "$$GIT_DIR" || exit 0; \
+	  $(top_srcdir)/gitlog-to-changelog $(GITLOG_FLAGS) \
+	    >'$(distdir)/ChangeLog.gen' && \
+	  mv -f '$(distdir)/ChangeLog.gen' '$(distdir)/ChangeLog'
+	rm -f '$(distdir)/ChangeLog.gen'
+.PHONY: generate-changelog
+
+GENERIC_V   = $(GENERIC_V_@AM_V@)
+GENERIC_V_  = $(GENERIC_V_@AM_DEFAULT_V@)
+GENERIC_V_0 = @printf '%2.0s%$(DX_ALIGN_V)s %s\n'
+
+TEST_DISTRIBUTION = false
+TEST_DISTRIBUTION_OR_ERROR = if $(TEST_DISTRIBUTION); \
+  then echo 'Proceeding anyway...'; \
+  else echo 'Run $(MAKE) TEST_DISTRIBUTION=true to ignore this failure.'; \
+       false; \
+  fi
+
+distcheck-hook:
+	$(GENERIC_V) : 'CHECK   ' ChangeLog; \
+	  $(AWK) '/^Stub/ { print FILENAME ":" NR ":", $$0; exit 1 }' \
+	    $(distdir)/ChangeLog || { \
+	      echo 'ERROR: *** Packaged ChangeLog was not properly generated from git log.'; \
+	      echo '       *** The source version was used instead, but this appears to'; \
+	      echo '       *** be the stub from a git checkout.  The "git" and "perl"'; \
+	      echo '       *** programs are required for ChangeLog generation to work.'; \
+	      $(TEST_DISTRIBUTION_OR_ERROR); } >&2
+
 # Supporting rules for bison/flex.
 
 BISON_V   = $(BISON_V_@AM_V@)
diff --git a/m4/gnulib-cache.m4 b/m4/gnulib-cache.m4
index 5faa6b6..5223b7d 100644
--- a/m4/gnulib-cache.m4
+++ b/m4/gnulib-cache.m4
@@ -41,6 +41,7 @@
 #  --no-vc-files \
 #  getopt-gnu \
 #  gettext-h \
+#  gitlog-to-changelog \
 #  localcharset \
 #  lock \
 #  readline \
@@ -52,6 +53,7 @@ gl_LOCAL_DIR([])
 gl_MODULES([
   getopt-gnu
   gettext-h
+  gitlog-to-changelog
   localcharset
   lock
   readline
-- 
2.43.2