fix: track compile errors and send hmr update when returning to working state

.changeset/nervous-jobs-remain.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/vite-plugin-svelte': patch
+---
+
+fix hmr not updating a component when returning to the last working state from an error state

packages/vite-plugin-svelte/src/handle-hot-update.ts

@@ -15,33 +15,39 @@ export async function handleHotUpdate(
 	cache: VitePluginSvelteCache,
 	options: ResolvedOptions
 ): Promise<ModuleNode[] | void> {
-	const { read, server } = ctx;
-
-	const cachedJS = cache.getJS(svelteRequest);
-	if (!cachedJS) {
+	if (!cache.has(svelteRequest)) {
 		// file hasn't been requested yet (e.g. async component)
-		log.debug(`handleHotUpdate first call ${svelteRequest.id}`);
+		log.debug(`handleHotUpdate called before initial transform for ${svelteRequest.id}`);
 		return;
 	}
+	const { read, server } = ctx;
+
+	const cachedJS = cache.getJS(svelteRequest);
 	const cachedCss = cache.getCSS(svelteRequest);
 
 	const content = await read();
-	const compileData: CompileData = await compileSvelte(svelteRequest, content, options);
-	cache.update(compileData);
+	let compileData: CompileData;
+	try {
+		compileData = await compileSvelte(svelteRequest, content, options);
+		cache.update(compileData);
+	} catch (e) {
+		cache.setError(svelteRequest, e);
+		throw e;
+	}
 
 	const affectedModules = new Set<ModuleNode | undefined>();
 
 	const cssModule = server.moduleGraph.getModuleById(svelteRequest.cssId);
 	const mainModule = server.moduleGraph.getModuleById(svelteRequest.id);
 	const cssUpdated = cssModule && cssChanged(cachedCss, compileData.compiled.css);
 	if (cssUpdated) {
-		log.debug('handleHotUpdate css changed');
+		log.debug(`handleHotUpdate css changed for ${svelteRequest.cssId}`);
 		affectedModules.add(cssModule);
 	}
 	const jsUpdated =
 		mainModule && jsChanged(cachedJS, compileData.compiled.js, svelteRequest.filename);
 	if (jsUpdated) {
-		log.debug('handleHotUpdate js changed');
+		log.debug(`handleHotUpdate js changed for ${svelteRequest.id}`);
 		affectedModules.add(mainModule);
 	}
 

packages/vite-plugin-svelte/src/index.ts

@@ -183,6 +183,7 @@ export function svelte(inlineOptions?: Partial<Options>): Plugin[] {
 				try {
 					compileData = await compileSvelte(svelteRequest, code, options);
 				} catch (e) {
+					cache.setError(svelteRequest, e);
 					throw toRollupError(e, options);
 				}
 				logCompilerWarnings(compileData.compiled.warnings, options);
@@ -209,7 +210,11 @@ export function svelte(inlineOptions?: Partial<Options>): Plugin[] {
 				}
 				const svelteRequest = requestParser(ctx.file, false, ctx.timestamp);
 				if (svelteRequest) {
-					return handleHotUpdate(compileSvelte, ctx, svelteRequest, cache, options);
+					try {
+						return handleHotUpdate(compileSvelte, ctx, svelteRequest, cache, options);
+					} catch (e) {
+						throw toRollupError(e, options);
+					}
 				}
 			}
 		}

packages/vite-plugin-svelte/src/utils/vite-plugin-svelte-cache.ts

@@ -7,13 +7,27 @@ export class VitePluginSvelteCache {
 	private _dependencies = new Map<string, string[]>();
 	private _dependants = new Map<string, Set<string>>();
 	private _resolvedSvelteFields = new Map<string, string>();
+	private _errors = new Map<string, any>();
 
 	public update(compileData: CompileData) {
+		this._errors.delete(compileData.normalizedFilename);
 		this.updateCSS(compileData);
 		this.updateJS(compileData);
 		this.updateDependencies(compileData);
 	}
 
+	public has(svelteRequest: SvelteRequest) {
+		const id = svelteRequest.normalizedFilename;
+		return this._errors.has(id) || this._js.has(id) || this._css.has(id);
+	}
+
+	public setError(svelteRequest: SvelteRequest, error: any) {
+		// keep dependency info, otherwise errors in dependants would not trigger an update after fixing
+		// because they are no longer watched
+		this.remove(svelteRequest, true);
+		this._errors.set(svelteRequest.normalizedFilename, error);
+	}
+
 	private updateCSS(compileData: CompileData) {
 		this._css.set(compileData.normalizedFilename, compileData.compiled.css);
 	}
@@ -43,26 +57,32 @@ export class VitePluginSvelteCache {
 		});
 	}
 
-	public remove(svelteRequest: SvelteRequest): boolean {
+	public remove(svelteRequest: SvelteRequest, keepDependencies: boolean = false): boolean {
 		const id = svelteRequest.normalizedFilename;
 		let removed = false;
+		if (this._errors.delete(id)) {
+			removed = true;
+		}
 		if (this._js.delete(id)) {
 			removed = true;
 		}
 		if (this._css.delete(id)) {
 			removed = true;
 		}
-		const dependencies = this._dependencies.get(id);
-		if (dependencies) {
-			removed = true;
-			dependencies.forEach((d) => {
-				const dependants = this._dependants.get(d);
-				if (dependants && dependants.has(svelteRequest.filename)) {
-					dependants.delete(svelteRequest.filename);
-				}
-			});
-			this._dependencies.delete(id);
+		if (!keepDependencies) {
+			const dependencies = this._dependencies.get(id);
+			if (dependencies) {
+				removed = true;
+				dependencies.forEach((d) => {
+					const dependants = this._dependants.get(d);
+					if (dependants && dependants.has(svelteRequest.filename)) {
+						dependants.delete(svelteRequest.filename);
+					}
+				});
+				this._dependencies.delete(id);
+			}
 		}
+
 		return removed;
 	}
 
@@ -77,6 +97,10 @@ export class VitePluginSvelteCache {
 		}
 	}
 
+	public getError(svelteRequest: SvelteRequest) {
+		return this._errors.get(svelteRequest.normalizedFilename);
+	}
+
 	public getDependants(path: string): string[] {
 		const dependants = this._dependants.get(path);
 		return dependants ? [...dependants] : [];