Enable supplying a commit message template

src/index.ts

@@ -1,4 +1,5 @@
 import { makeNixCommandArgs } from "./nix.js";
+import { renderCommitMessage } from "./template.js";
 import * as actionsCore from "@actions/core";
 import * as actionsExec from "@actions/exec";
 import { DetSysAction, inputs } from "detsys-ts";
@@ -12,6 +13,7 @@ const EVENT_EXECUTION_FAILURE = "execution_failure";
 
 class UpdateFlakeLockAction extends DetSysAction {
   private commitMessage: string;
+  private commitMessageTemplate: string;
   private nixOptions: string[];
   private flakeInputs: string[];
   private pathToFlakeDir: string | null;
@@ -26,6 +28,7 @@ class UpdateFlakeLockAction extends DetSysAction {
     });
 
     this.commitMessage = inputs.getString("commit-msg");
+    this.commitMessageTemplate = inputs.getString("commit-msg-template");
     this.flakeInputs = inputs.getArrayOfStrings("inputs", "space");
     this.nixOptions = inputs.getArrayOfStrings("nix-options", "space");
     this.pathToFlakeDir = inputs.getStringOrNull("path-to-flake-dir");
@@ -57,6 +60,12 @@ class UpdateFlakeLockAction extends DetSysAction {
 
     actionsCore.debug(`Running flake lock update in directory \`${flakeDir}\``);
 
+    const flakeDotLock = `${flakeDir}/flake.lock`;
+    const commitMessage =
+      this.commitMessage !== ""
+        ? this.commitMessage
+        : renderCommitMessage(this.commitMessageTemplate, flakeDotLock);
+
     // Nix command of this form:
     // nix ${maybe nix options} flake ${"update" or "lock"} ${maybe --update-input flags} --commit-lock-file --commit-lockfile-summary ${commit message}
     // Example commands:
@@ -65,7 +74,7 @@ class UpdateFlakeLockAction extends DetSysAction {
     const nixCommandArgs: string[] = makeNixCommandArgs(
       this.nixOptions,
       this.flakeInputs,
-      this.commitMessage,
+      commitMessage,
     );
 
     actionsCore.debug(

src/template.test.ts

@@ -0,0 +1,31 @@
+import { renderCommitMessage } from "./template.js";
+import { describe, expect, test } from "vitest";
+
+describe("templating", () => {
+  test("commit message", () => {
+    type TestCase = {
+      template: string;
+      flakeDotLock: string;
+      expected: string;
+    };
+
+    const testCases: TestCase[] = [
+      {
+        template: "Updating lockfile at {{ flake_dot_lock }}",
+        flakeDotLock: "./flake.lock",
+        expected: "Updating lockfile at ./flake.lock",
+      },
+      {
+        template:
+          "Here I go doing some updating of my pristine flake.lock at {{ flake_dot_lock }}",
+        flakeDotLock: "subflake/flake.lock",
+        expected:
+          "Here I go doing some updating of my pristine flake.lock at subflake/flake.lock",
+      },
+    ];
+
+    testCases.forEach(({ template, flakeDotLock, expected }) => {
+      expect(renderCommitMessage(template, flakeDotLock)).toEqual(expected);
+    });
+  });
+});

src/template.ts

@@ -0,0 +1,13 @@
+import Handlebars from "handlebars";
+
+export function renderCommitMessage(
+  template: string,
+  flakeDotLock: string,
+): string {
+  return render(template, { flake_dot_lock: flakeDotLock });
+}
+
+function render(template: string, inputs: Record<string, string>): string {
+  const tpl = Handlebars.compile(template);
+  return tpl(inputs);
+}