fix(vite-plugin): keep watching config changes after a failed restart

.changeset/config-watch-failed-restart.md

@@ -0,0 +1,9 @@
+---
+"@cloudflare/vite-plugin": patch
+---
+
+Keep watching config changes after a failed dev server restart
+
+Previously, when a config change made the dev server restart fail — for example because the updated Worker config was invalid — the plugin stopped watching config changes entirely: the change handler (covering the Worker config files, local dev vars, and the assets configuration) removed itself before restarting, and only a successfully created server would register a fresh one. Since Vite keeps the current server running when a restart fails, every subsequent config change (including the one that fixes the config) was silently ignored for the rest of the session.
+
+The handler now stays registered and guards against re-entrant restarts instead, so fixing the config restarts the dev server as expected.

packages/vite-plugin-cloudflare/playground/config-changes/__tests__/config-changes.spec.ts

@@ -70,4 +70,53 @@ describe("config-changes", () => {
 			}, WAIT_FOR_OPTIONS);
 		}
 	);
+
+	test.runIf(!isBuild)(
+		"applies further Worker config changes after a broken config update",
+		async ({ expect }) => {
+			await vi.waitFor(
+				async () =>
+					expect(await getTextResponse()).toContain(
+						'The value of MY_VAR is "one"'
+					),
+				WAIT_FOR_OPTIONS
+			);
+
+			mockFileChange(path.join(__dirname, "../wrangler.json"), (content) =>
+				JSON.stringify({
+					...JSON.parse(content),
+					main: "./src/missing-after-broken-update.ts",
+				})
+			);
+
+			await vi.waitFor(
+				() =>
+					expect(serverLogs.errors.join()).toContain(
+						"missing-after-broken-update"
+					),
+				WAIT_FOR_OPTIONS
+			);
+
+			// The restart triggered by the broken config fails and keeps the
+			// current server running. A subsequent config change must still be
+			// picked up.
+			mockFileChange(path.join(__dirname, "../wrangler.json"), (content) =>
+				JSON.stringify({
+					...JSON.parse(content),
+					main: "./src/index.ts",
+					vars: {
+						MY_VAR: "three",
+					},
+				})
+			);
+
+			await vi.waitFor(
+				async () =>
+					expect(await getTextResponse()).toContain(
+						'The value of MY_VAR is "three"'
+					),
+				WAIT_FOR_OPTIONS
+			);
+		}
+	);
 });

packages/vite-plugin-cloudflare/src/plugins/config.ts

@@ -113,9 +113,22 @@ export const configPlugin = createPlugin("config", (ctx) => {
 			ctx.setHasShownWorkerConfigWarnings(false);
 		},
 		configureServer(viteDevServer) {
+			// This variable is used to guard against config changes triggering
+			// a restart while another restart is already in flight. Note that we are
+			// deliberately not calling `watcher.off` since on failed restarts
+			// (e.g. the changed config is invalid) vite would resolve without replacing
+			// the server, so a removed handler would never be re-registered and
+			// config changes, including the one that fixes the config, would be
+			// ignored for the rest of the session.
+			let restartInFlight = false;
+
 			const configChangedHandler = async (changedFilePath: string) => {
 				assertIsNotPreview(ctx);
 
+				if (restartInFlight) {
+					return;
+				}
+
 				if (
 					ctx.resolvedPluginConfig.configPaths.has(changedFilePath) ||
 					hasLocalDevVarsFileChanged(
@@ -129,9 +142,13 @@ export const configPlugin = createPlugin("config", (ctx) => {
 					)
 				) {
 					debuglog("Config changed: " + changedFilePath);
-					viteDevServer.watcher.off("change", configChangedHandler);
+					restartInFlight = true;
 					debuglog("Restarting dev server and aborting previous setup");
-					await viteDevServer.restart();
+					try {
+						await viteDevServer.restart();
+					} finally {
+						restartInFlight = false;
+					}
 				}
 			};