fix: preprocess error reporting

.changeset/pretty-hairs-press.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/vite-plugin-svelte': patch
+---
+
+include stack and filename in error reporting for svelte preprocess errors

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

@@ -170,7 +170,7 @@ export function svelte(inlineOptions?: Partial<Options>): Plugin {
 			try {
 				compileData = await compileSvelte(svelteRequest, code, options);
 			} catch (e) {
-				throw toRollupError(e);
+				throw toRollupError(e, options);
 			}
 			logCompilerWarnings(compileData.compiled.warnings, options);
 			cache.update(compileData);

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

@@ -37,7 +37,13 @@ const _createCompileSvelte = (makeHot: Function) =>
 		let preprocessed;
 
 		if (options.preprocess) {
-			preprocessed = await preprocess(code, options.preprocess, { filename });
+			try {
+				preprocessed = await preprocess(code, options.preprocess, { filename });
+			} catch (e) {
+				e.message = `Error while preprocessing ${filename}${e.message ? ` - ${e.message}` : ''}`;
+				throw e;
+			}
+
 			if (preprocessed.dependencies) dependencies.push(...preprocessed.dependencies);
 			if (preprocessed.map) compileOptions.sourcemap = preprocessed.map;
 		}

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

@@ -1,5 +1,5 @@
 import { RollupError } from 'rollup';
-import { Warning } from './options';
+import { ResolvedOptions, Warning } from './options';
 import { buildExtendedLogMessage } from './log';
 import { PartialMessage } from 'esbuild';
 
@@ -8,15 +8,15 @@ import { PartialMessage } from 'esbuild';
  * @param error a svelte compiler error, which is a mix of Warning and an error
  * @returns {RollupError} the converted error
  */
-export function toRollupError(error: Warning & Error): RollupError {
-	const { filename, frame, start, code, name } = error;
+export function toRollupError(error: Warning & Error, options: ResolvedOptions): RollupError {
+	const { filename, frame, start, code, name, stack } = error;
 	const rollupError: RollupError = {
 		name, // needed otherwise sveltekit coalesce_to_error turns it into a string
 		id: filename,
 		message: buildExtendedLogMessage(error), // include filename:line:column so that it's clickable
 		frame: formatFrameForVite(frame),
 		code,
-		stack: ''
+		stack: options.isBuild || options.isDebug || !frame ? stack : ''
 	};
 	if (start) {
 		rollupError.loc = {
@@ -33,8 +33,8 @@ export function toRollupError(error: Warning & Error): RollupError {
  * @param error a svelte compiler error, which is a mix of Warning and an error
  * @returns {PartialMessage} the converted error
  */
-export function toESBuildError(error: Warning & Error): PartialMessage {
-	const { filename, frame, start } = error;
+export function toESBuildError(error: Warning & Error, options: ResolvedOptions): PartialMessage {
+	const { filename, frame, start, stack } = error;
 	const partialMessage: PartialMessage = {
 		text: buildExtendedLogMessage(error)
 	};
@@ -46,6 +46,9 @@ export function toESBuildError(error: Warning & Error): PartialMessage {
 			lineText: lineFromFrame(start.line, frame) // needed to get a meaningful error message on cli
 		};
 	}
+	if (options.isBuild || options.isDebug || !frame) {
+		partialMessage.detail = stack;
+	}
 	return partialMessage;
 }
 

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

@@ -27,7 +27,7 @@ export function esbuildSveltePlugin(options: ResolvedOptions): EsbuildPlugin {
 					const contents = await compileSvelte(options, { filename, code });
 					return { contents };
 				} catch (e) {
-					return { errors: [toESBuildError(e)] };
+					return { errors: [toESBuildError(e, options)] };
 				}
 			});
 		}
@@ -73,7 +73,12 @@ async function compileSvelte(
 	let preprocessed;
 
 	if (options.preprocess) {
-		preprocessed = await preprocess(code, options.preprocess, { filename });
+		try {
+			preprocessed = await preprocess(code, options.preprocess, { filename });
+		} catch (e) {
+			e.message = `Error while preprocessing ${filename}${e.message ? ` - ${e.message}` : ''}`;
+			throw e;
+		}
 		if (preprocessed.map) compileOptions.sourcemap = preprocessed.map;
 	}
 

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

@@ -164,7 +164,10 @@ export function buildExtendedLogMessage(w: Warning) {
 		parts.push(':', w.start.line, ':', w.start.column);
 	}
 	if (w.message) {
-		parts.push(' ', w.message);
+		if (parts.length > 0) {
+			parts.push(' ');
+		}
+		parts.push(w.message);
 	}
 	return parts.join('');
 }

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

@@ -82,7 +82,8 @@ export async function preResolveOptions(
 		// extras
 		root: viteConfigWithResolvedRoot.root!,
 		isBuild: viteEnv.command === 'build',
-		isServe: viteEnv.command === 'serve'
+		isServe: viteEnv.command === 'serve',
+		isDebug: process.env.DEBUG != null
 	};
 	// configFile of svelteConfig contains the absolute path it was loaded from,
 	// prefer it over the possibly relative inline path
@@ -491,6 +492,7 @@ export interface PreResolvedOptions extends Options {
 	root: string;
 	isBuild: boolean;
 	isServe: boolean;
+	isDebug: boolean;
 }
 
 export interface ResolvedOptions extends PreResolvedOptions {