feat(commit): text templating in commit messages

cmd/commit_message.go

@@ -0,0 +1,48 @@
+/*
+Copyright © 2025 Lewis Wynne <lew@ily.rs>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+*/
+
+package cmd
+
+import (
+	"bytes"
+	"text/template"
+)
+
+// renderCommitMessage renders a commit message template. It extends the
+// shared template FuncMap with {{ summary }}, which returns the action
+// description for the current commit. On any error the raw template string
+// is returned so that commits are never blocked by a bad template.
+func renderCommitMessage(tmpl string, summary string) string {
+	funcMap := templateFuncMap()
+	funcMap["summary"] = func() string { return summary }
+
+	t, err := template.New("commit").Option("missingkey=zero").Funcs(funcMap).Parse(tmpl)
+	if err != nil {
+		return tmpl
+	}
+
+	var buf bytes.Buffer
+	if err := t.Execute(&buf, nil); err != nil {
+		return tmpl
+	}
+	return buf.String()
+}