contrib: add commit-msg git hook

Add a script that deals with the proper formatting and ordering of git
trailers. Install it as commit-msg git hook so that everyone can benefit
from it.

Signed-off-by: Robin Jarry <robin@jarry.cc>
Tested-by: Bence Ferdinandy <bence@ferdinandy.com>

3 files changed, 83 insertions, 0 deletions

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 9337a3c2..1a4d0bd2 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -76,6 +76,7 @@ defaults:
     git config format.notes true
     git config notes.rewriteRef refs/notes/commits
     git config notes.rewriteMode concatenate
+    ln -s ../../contrib/commit-msg .git/hooks/commit-msg
     + ln -s ../../contrib/sendemail-validate .git/hooks/sendemail-validate
     + git config sendemail.validate true
 
diff --git a/GNUmakefile b/GNUmakefile
index cd86c096..274f2c6d 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -114,6 +114,8 @@ gitconfig:
 	git config notes.rewriteRef refs/notes/commits
 	git config notes.rewriteMode concatenate
 	@mkdir -p .git/hooks
+	@rm -f .git/hooks/commit-msg*
+	ln -s ../../contrib/commit-msg .git/hooks/commit-msg
 	@rm -f .git/hooks/sendemail-validate*
 	@if grep -q GIT_SENDEMAIL_FILE_COUNTER `git --exec-path`/git-send-email 2>/dev/null; then \
 		set -xe; \
diff --git a/contrib/commit-msg b/contrib/commit-msg
new file mode 100755
index 00000000..add67177
--- /dev/null
+++ b/contrib/commit-msg
@@ -0,0 +1,80 @@
+#!/bin/sh
+
+set -e
+
+debug() {
+	if [ "$GIT_TRAILER_DEBUG" = 1 ]; then
+		"$@" >&2
+	fi
+}
+
+trailer_order="
+Closes:
+Fixes:
+Implements:
+References:
+Link:
+Changelog-added:
+Changelog-fixed:
+Changelog-changed:
+Changelog-deprecated:
+Cc:
+Suggested-by:
+Requested-by:
+Reported-by:
+Co-authored-by:
+Signed-off-by:
+Tested-by:
+Reviewed-by:
+Acked-by:
+"
+file=${1?file}
+tmp=$(mktemp)
+trap "rm -f $tmp" EXIT
+
+# Read unfolded trailers and normalize case.
+git interpret-trailers --parse --trim-empty "$file" |
+while read -r key value; do
+	# Force title case on trailer key.
+	first_letter=$(echo "$key" | sed 's/^\(.\).*/\1/' | tr '[:lower:]' '[:upper:]')
+	other_letters=$(echo "$key" | sed 's/^.\(.*\)/\1/' | tr '[:upper:]' '[:lower:]')
+	key="$first_letter$other_letters"
+
+	# Find sort order of this key.
+	order=$(echo "$trailer_order" | grep -Fxn "$key" | sed -n 's/^\([0-9]\+\):.*/\1/p')
+	if [ -z "$order" ]; then
+		echo "warning: unknown trailer '$key'" >&2
+		# Unknown trailers are always first.
+		order="0"
+	fi
+
+	echo "$order $key $value"
+done |
+# Sort trailers according to their numeric order, trim the numeric order.
+LC_ALL=C sort -n | sed 's/^[0-9]\+ //' > "$tmp"
+
+debug echo ==== sanitized trailers ====
+debug cat "$tmp"
+
+# Unfortunately, reordering trailers is not possible at the moment. Delete all
+# trailers first. The only way to do it is to force replace existing trailers
+# with empty values and trim empty trailers one by one.
+while read -r key value; do
+	git interpret-trailers --in-place --if-exists=replace \
+		--trailer="$key " "$file"
+	git interpret-trailers --in-place --trim-empty "$file"
+done < "$tmp"
+
+set --
+while read -r trailer; do
+	case "$trailer" in
+	Changelog-*)
+		# Wrap changelog entries indenting with a space.
+		trailer=$(echo "$trailer" | fmt -w 72 | sed '2,$s/^/ /')
+		;;
+	esac
+	set -- "$@" --trailer="$trailer"
+done < "$tmp"
+
+# Remove duplicate "key: value" trailers (e.g. duplicate signed-off-by).
+git interpret-trailers --in-place --if-exists=addIfDifferent "$@" "$file"