ensured deterministic manifest serialization

this avoids meaningless file changes due to random insertion order

Author: FND

lib/manifest.js

@@ -6,13 +6,13 @@ let { abort } = require("./util");
 let path = require("path");
 
 module.exports = class Manifest {
-	constructor(referenceDir, { target, key, value, baseURI, webRoot }) {
+	constructor(referenceDir, { target, key, value, baseURI, webRoot } = {}) {
 		if(target) {
 			this.filepath = resolvePath(target, referenceDir, {
 				enforceRelative: true
 			});
 		}
-		this._index = {};
+		this._index = new Map();
 
 		if(key === "short") {
 			this.keyTransform = (fp, targetDir) => path.relative(targetDir, fp);
@@ -34,19 +34,24 @@ module.exports = class Manifest {
 	}
 
 	get(originalPath) {
-		return this._index[originalPath];
+		return this._index.get(originalPath);
 	}
 
 	set(originalPath, actualPath, targetDir) {
 		let key = this.keyTransform(originalPath, targetDir);
 		let uri = this.valueTransform(actualPath);
-		this._index[key] = uri;
+		this._index.set(key, uri);
 
 		let fp = this.filepath;
 		return fp ? createFile(fp, this.toJSON()) : Promise.resolve(null);
 	}
 
 	toJSON() {
-		return JSON.stringify(this._index) + "\n";
+		let index = this._index;
+		let manifest = Array.from(index.keys()).sort().reduce((memo, key) => {
+			memo[key] = index.get(key);
+			return memo;
+		}, {});
+		return JSON.stringify(manifest) + "\n";
 	}
 };

test/test_manager.js

@@ -8,20 +8,19 @@ let assert = require("assert");
 let assertSame = assert.strictEqual;
 
 describe("asset manager", _ => {
+	let root = path.resolve(__dirname, "fixtures");
 	let cwd;
 
 	before(() => {
 		cwd = process.cwd();
+		process.chdir(root);
 	});
 
 	after(() => {
 		process.chdir(cwd);
 	});
 
 	it("resolves file paths for local modules and third-party packages", () => {
-		let root = path.resolve(__dirname, "fixtures");
-		process.chdir(root);
-
 		let { resolvePath } = new AssetManager(root);
 
 		let filepath = resolvePath("dummy/src.js");

test/test_manifest.js

@@ -0,0 +1,42 @@
+/* global describe, before, after, it */
+"use strict";
+
+let Manifest = require("../lib/manifest");
+let path = require("path");
+let assert = require("assert");
+
+let assertSame = assert.strictEqual;
+
+describe("manifest", _ => {
+	let root = path.resolve(__dirname, "fixtures");
+	let cwd;
+
+	before(() => {
+		cwd = process.cwd();
+		process.chdir(root);
+	});
+
+	after(() => {
+		process.chdir(cwd);
+	});
+
+	it("maps original to actual file names with deterministic serialization", () => {
+		let manifest = new Manifest(root);
+		return manifest.set("foo.png", "foo-abc123.png").
+			then(_ => { // eslint-disable-next-line quotes
+				assertSame(manifest.toJSON(), `{"foo.png":"/foo-abc123.png"}\n`);
+
+				return manifest.set("bar.css", "bar-def456.css");
+			}).
+			then(_ => {
+				assertSame(manifest.toJSON(), // eslint-disable-next-line quotes
+						`{"bar.css":"/bar-def456.css","foo.png":"/foo-abc123.png"}\n`);
+
+				return manifest.set("xox.js", "xox-ghi789.js");
+			}).
+			then(_ => {
+				assertSame(manifest.toJSON(), // eslint-disable-next-line quotes
+						`{"bar.css":"/bar-def456.css","foo.png":"/foo-abc123.png","xox.js":"/xox-ghi789.js"}\n`);
+			});
+	});
+});