Allow HMR status handlers to return a Promise

The HMR system will wait until the promise settles before continuing.

lib/hmr/HotModuleReplacement.runtime.js

@@ -9,6 +9,7 @@ var $interceptModuleExecution$ = undefined;
 var $moduleCache$ = undefined;
 // eslint-disable-next-line no-unused-vars
 var $hmrModuleData$ = undefined;
+/** @type {() => Promise}  */
 var $hmrDownloadManifest$ = undefined;
 var $hmrDownloadUpdateHandlers$ = undefined;
 var $hmrInvalidateModuleHandlers$ = undefined;
@@ -209,8 +210,12 @@ module.exports = function () {
 
 	function setStatus(newStatus) {
 		currentStatus = newStatus;
+		var results = [];
+
 		for (var i = 0; i < registeredStatusHandlers.length; i++)
-			registeredStatusHandlers[i].call(null, newStatus);
+			results[i] = registeredStatusHandlers[i].call(null, newStatus);
+
+		return Promise.all(results);
 	}
 
 	function trackBlockingPromise(promise) {
@@ -219,7 +224,7 @@ module.exports = function () {
 				setStatus("prepare");
 				blockingPromises.push(promise);
 				waitForBlockingPromises(function () {
-					setStatus("ready");
+					return setStatus("ready");
 				});
 				return promise;
 			case "prepare":
@@ -243,15 +248,14 @@ module.exports = function () {
 		if (currentStatus !== "idle") {
 			throw new Error("check() is only allowed in idle status");
 		}
-		setStatus("check");
+		return setStatus("check")
-		return $hmrDownloadManifest$().then(function (update) {
+			.then($hmrDownloadManifest$)
+			.then(function (update) {
 				if (!update) {
-				setStatus(applyInvalidatedModules() ? "ready" : "idle");
+					return setStatus(applyInvalidatedModules() ? "ready" : "idle");
-				return null;
 				}
 
-			setStatus("prepare");
+				return setStatus("prepare").then(function () {
-
 					var updatedModules = [];
 					blockingPromises = [];
 					currentUpdateApplyHandlers = [];
@@ -277,13 +281,14 @@ module.exports = function () {
 							if (applyOnUpdate) {
 								return internalApply(applyOnUpdate);
 							} else {
-						setStatus("ready");
+								return setStatus("ready").then(function () {
-
 									return updatedModules;
+								});
 							}
 						});
 					});
 				});
+			});
 	}
 
 	function hotApply(options) {
@@ -312,22 +317,19 @@ module.exports = function () {
 			.filter(Boolean);
 
 		if (errors.length > 0) {
-			setStatus("abort");
+			return setStatus("abort").then(function () {
-			return Promise.resolve().then(function () {
 				throw errors[0];
 			});
 		}
 
 		// Now in "dispose" phase
-		setStatus("dispose");
+		return setStatus("dispose").then(function () {
-
 			results.forEach(function (result) {
 				if (result.dispose) result.dispose();
 			});
 
 			// Now in "apply" phase
-		setStatus("apply");
+			return setStatus("apply").then(function () {
-
 				var error;
 				var reportError = function (err) {
 					if (!error) error = err;
@@ -347,8 +349,7 @@ module.exports = function () {
 
 				// handle errors in accept handlers and self accepted module load
 				if (error) {
-			setStatus("fail");
+					return setStatus("fail").then(function () {
-			return Promise.resolve().then(function () {
 						throw error;
 					});
 				}
@@ -362,8 +363,11 @@ module.exports = function () {
 					});
 				}
 
-		setStatus("idle");
+				return setStatus("idle").then(function () {
-		return Promise.resolve(outdatedModules);
+					return outdatedModules;
+				});
+			});
+		});
 	}
 
 	function applyInvalidatedModules() {

test/HotTestCases.template.js

@@ -250,7 +250,7 @@ const describeCases = config => {
 												return JSON.parse(fs.readFileSync(p, "utf-8"));
 											} else {
 												const fn = vm.runInThisContext(
-													"(function(require, module, exports, __dirname, __filename, it, beforeEach, afterEach, expect, self, window, fetch, document, importScripts, Worker, EventSource, NEXT, STATS) {" +
+													"(function(require, module, exports, __dirname, __filename, it, beforeEach, afterEach, expect, jest, self, window, fetch, document, importScripts, Worker, EventSource, NEXT, STATS) {" +
 														"global.expect = expect;" +
 														'function nsObj(m) { Object.defineProperty(m, Symbol.toStringTag, { value: "Module" }); return m; }' +
 														fs.readFileSync(p, "utf-8") +
@@ -271,6 +271,7 @@ const describeCases = config => {
 													_beforeEach,
 													_afterEach,
 													expect,
+													jest,
 													window,
 													window,
 													window.fetch,

test/hotCases/invalidate/during-idle/index.js

@@ -11,9 +11,10 @@ it("should allow to invalidate and reload a file", () => {
 	expect(module.hot.status()).toBe("ready");
 	c.invalidate();
 	expect(module.hot.status()).toBe("ready");
-	module.hot.apply();
+	module.hot.apply().then(function () {
 		expect(module.hot.status()).toBe("idle");
 		expect(a.value).not.toBe(oldA);
 		expect(b.value).not.toBe(oldB);
 		expect(c.value).toBe(oldC);
+	});
 });

test/hotCases/status/accept/file.js

@@ -0,0 +1,3 @@
+module.exports = 1;
+---
+module.exports = 2;

test/hotCases/status/accept/index.js

@@ -0,0 +1,21 @@
+var value = require("./file");
+
+it("should wait until promises returned by status handlers are fulfilled", (done) => {
+	var handler = jest.fn(status => {
+		return Promise.resolve().then(() => {
+			expect(status).toBe(module.hot.status());
+		});
+	});
+	module.hot.addStatusHandler(handler);
+	module.hot.accept("./file", () => {
+		value = require("./file");
+		done();
+	});
+	NEXT(require("../../update")(done, undefined, () => {
+		expect(module.hot.status()).toBe("idle");
+		
+		expect(handler.mock.calls).toBe([['check'], ['prepare'], ['dispose'], ['apply'], ['idle']]);
+		done();
+}));
+});
+