feat(git): custom merge message hook

.gitignore

@@ -36,6 +36,9 @@ git/*
 git/config.d/*
 !git/config.d/aflabs.conf
 !git/config.d/flare.conf
+!git/hooks
+git/hooks/*
+!git/hooks/merge-msg
 
 # ghostty
 !ghostty

git/config

@@ -73,3 +73,7 @@
 
 [includeIf "gitdir:~/git/gitlab.com/flare-foundation/"]
 	path = ~/.config/git/config.d/flare.conf
+
+[hook "merge-msg"]
+	command = ~/.config/git/hooks/merge-msg
+	event = prepare-commit-msg

git/hooks/merge-msg

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# rewrite default merge subject to `merge: <branch with dashes as spaces>`
+
+msg_file="$1"
+source="$2"
+
+[[ "$source" == "merge" ]] || exit 0
+
+subject=$(head -n1 "$msg_file")
+
+if [[ "$subject" =~ ^Merge\ remote-tracking\ branch\ \'[^/]+/([^\']+)\' ]]; then
+	branch="${BASH_REMATCH[1]}"
+elif [[ "$subject" =~ ^Merge\ branch\ \'([^\']+)\' ]]; then
+	branch="${BASH_REMATCH[1]}"
+else
+	exit 0
+fi
+
+{
+	printf 'merge: %s\n' "${branch//-/ }"
+	tail -n +2 "$msg_file"
+} > "$msg_file.tmp" && mv "$msg_file.tmp" "$msg_file"