feat: remove experimental.generateMissingPreprocessorSourcemaps (#514)

.changeset/funny-dryers-do.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/vite-plugin-svelte': patch
+---
+
+remove experimental.generateMissingPreprocessorSourcemaps

docs/config.md

@@ -251,13 +251,6 @@ export default {
 
   Use extra preprocessors that delegate style and TypeScript preprocessing to native Vite plugins. TypeScript will be transformed with esbuild. Styles will be transformed using [Vite's CSS plugin](https://vitejs.dev/guide/features.html#css), which handles `@imports`, `url()` references, PostCSS, CSS Modules, and `.scss`/`.sass`/`.less`/`.styl`/`.stylus` files. Do not use together with TypeScript or style preprocessors from `svelte-preprocess` as attempts to transform the content twice will fail!
 
-### generateMissingPreprocessorSourcemaps
-
-- **Type:** `boolean`
-- **Default:** `false`
-
-  If a preprocessor does not provide a sourcemap, a best-effort fallback sourcemap will be provided. This option requires [diff-match-patch](https://github.com/google/diff-match-patch) to be installed as a peer dependency.
-
 ### dynamicCompileOptions
 
 - **Type:**

packages/vite-plugin-svelte/package.json

@@ -53,19 +53,11 @@
     "vitefu": "^0.2.2"
   },
   "peerDependencies": {
-    "diff-match-patch": "^1.0.5",
     "svelte": "^3.44.0",
     "vite": "^3.0.0"
   },
-  "peerDependenciesMeta": {
-    "diff-match-patch": {
-      "optional": true
-    }
-  },
   "devDependencies": {
     "@types/debug": "^4.1.7",
-    "@types/diff-match-patch": "^1.0.32",
-    "diff-match-patch": "^1.0.5",
     "esbuild": "^0.15.16",
     "rollup": "^2.79.1",
     "svelte": "^3.53.1",

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

@@ -315,6 +315,9 @@ function handleDeprecatedOptions(options: ResolvedOptions) {
 			'experimental.prebundleSvelteLibraries is no longer experimental and has moved to prebundleSvelteLibraries'
 		);
 	}
+	if ((options.experimental as any)?.generateMissingPreprocessorSourcemaps) {
+		log.warn('experimental.generateMissingPreprocessorSourcemaps has been removed.');
+	}
 }
 
 // vite passes unresolved `root`option to config hook but we need the resolved value, so do it here
@@ -693,15 +696,6 @@ export interface ExperimentalOptions {
 	 */
 	useVitePreprocess?: boolean;
 
-	/**
-	 * If a preprocessor does not provide a sourcemap, a best-effort fallback sourcemap will be provided.
-	 * This option requires `diff-match-patch` to be installed as a peer dependency.
-	 *
-	 * @see https://github.com/google/diff-match-patch
-	 * @default false
-	 */
-	generateMissingPreprocessorSourcemaps?: boolean;
-
 	/**
 	 * A function to update `compilerOptions` before compilation
 	 *

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

@@ -1,9 +1,8 @@
 import type { ResolvedConfig, Plugin } from 'vite';
 import MagicString from 'magic-string';
 import { preprocess } from 'svelte/compiler';
-import { PreprocessorGroup, Processed, ResolvedOptions } from './options';
+import { PreprocessorGroup, ResolvedOptions } from './options';
 import { log } from './log';
-import { buildSourceMap } from './sourcemap';
 import path from 'path';
 import { vitePreprocess } from '../preprocess';
 
@@ -117,67 +116,4 @@ export function addExtraPreprocessors(options: ResolvedOptions, config: Resolved
 			options.preprocess = [...prependPreprocessors, options.preprocess, ...appendPreprocessors];
 		}
 	}
-	const generateMissingSourceMaps = !!options.experimental?.generateMissingPreprocessorSourcemaps;
-	if (options.preprocess && generateMissingSourceMaps) {
-		options.preprocess = Array.isArray(options.preprocess)
-			? options.preprocess.map((p, i) => validateSourceMapOutputWrapper(p, i))
-			: validateSourceMapOutputWrapper(options.preprocess, 0);
-	}
-}
-
-function validateSourceMapOutputWrapper(group: PreprocessorGroup, i: number): PreprocessorGroup {
-	const wrapper: PreprocessorGroup = {};
-
-	for (const [processorType, processorFn] of Object.entries(group) as Array<
-		// eslint-disable-next-line no-unused-vars
-		[keyof PreprocessorGroup, (options: { filename?: string; content: string }) => Processed]
-	>) {
-		wrapper[processorType] = async (options) => {
-			const result = await processorFn(options);
-
-			if (result && result.code !== options.content) {
-				let invalidMap = false;
-				if (!result.map) {
-					invalidMap = true;
-					log.warn.enabled &&
-						log.warn.once(
-							`preprocessor at index ${i} did not return a sourcemap for ${processorType} transform`,
-							{
-								filename: options.filename,
-								type: processorType,
-								processor: processorFn.toString()
-							}
-						);
-				} else if ((result.map as any)?.mappings === '') {
-					invalidMap = true;
-					log.warn.enabled &&
-						log.warn.once(
-							`preprocessor at index ${i} returned an invalid empty sourcemap for ${processorType} transform`,
-							{
-								filename: options.filename,
-								type: processorType,
-								processor: processorFn.toString()
-							}
-						);
-				}
-				if (invalidMap) {
-					try {
-						const map = await buildSourceMap(options.content, result.code, options.filename);
-						if (map) {
-							log.debug.enabled &&
-								log.debug(
-									`adding generated sourcemap to preprocesor result for ${options.filename}`
-								);
-							result.map = map;
-						}
-					} catch (e) {
-						log.error(`failed to build sourcemap`, e);
-					}
-				}
-			}
-			return result;
-		};
-	}
-
-	return wrapper;
 }