feat: replace svelte-preprocess with barebones TS preprocessor (#2452)

Removes the need for a dependency on svelte-preprocess in svelte-language-server, since that was all we used it for.

closes:
- #1683 and #1259, because the situation no longer arises (because we no longer have svelte-preprocess inside the VS Code extension)
- #2391

packages/language-server/package.json

@@ -55,7 +55,6 @@
         "prettier": "~3.2.5",
         "prettier-plugin-svelte": "^3.2.2",
         "svelte": "^3.57.0",
-        "svelte-preprocess": "^5.1.3",
         "svelte2tsx": "workspace:~",
         "typescript": "^5.5.2",
         "typescript-auto-import-cache": "^0.3.3",

packages/language-server/src/importPackage.ts

@@ -1,7 +1,6 @@
 import { dirname, resolve } from 'path';
 import * as prettier from 'prettier';
 import * as svelte from 'svelte/compiler';
-import sveltePreprocess from 'svelte-preprocess';
 import { Logger } from './logger';
 
 /**
@@ -25,11 +24,15 @@ function dynamicRequire(dynamicFileToRequire: string): any {
     return require(dynamicFileToRequire);
 }
 
-export function getPackageInfo(packageName: string, fromPath: string) {
-    const paths = [__dirname];
+export function getPackageInfo(packageName: string, fromPath: string, use_fallback = true) {
+    const paths: string[] = [];
     if (isTrusted) {
-        paths.unshift(fromPath);
+        paths.push(fromPath);
     }
+    if (use_fallback) {
+        paths.push(__dirname);
+    }
+
     const packageJSONPath = require.resolve(`${packageName}/package.json`, {
         paths
     });
@@ -73,8 +76,13 @@ export function importSvelte(fromPath: string): typeof svelte {
     }
 }
 
-export function importSveltePreprocess(fromPath: string): typeof sveltePreprocess {
-    const pkg = getPackageInfo('svelte-preprocess', fromPath);
+/** Can throw because no fallback guaranteed */
+export function importSveltePreprocess(fromPath: string): any {
+    const pkg = getPackageInfo(
+        'svelte-preprocess',
+        fromPath,
+        false // svelte-language-server doesn't have a dependency on svelte-preprocess so we can't provide a fallback
+    );
     const main = resolve(pkg.path);
     Logger.debug('Using svelte-preprocess v' + pkg.version.full, 'from', main);
     return dynamicRequire(main);

packages/language-server/src/lib/documents/configLoader.ts

@@ -9,6 +9,7 @@ import _path from 'path';
 import _fs from 'fs';
 import { pathToFileURL, URL } from 'url';
 import { FileMap } from './fileCollection';
+import ts from 'typescript';
 
 export type InternalPreprocessorGroup = PreprocessorGroup & {
     /**
@@ -249,24 +250,49 @@ export class ConfigLoader {
     }
 
     private useFallbackPreprocessor(path: string, foundConfig: boolean): SvelteConfig {
-        Logger.log(
-            (foundConfig
-                ? 'Found svelte.config.js but there was an error loading it. '
-                : 'No svelte.config.js found. ') +
-                'Using https://github.com/sveltejs/svelte-preprocess as fallback'
-        );
-        const sveltePreprocess = importSveltePreprocess(path);
-        return {
-            preprocess: sveltePreprocess({
-                // 4.x does not have transpileOnly anymore, but if the user has version 3.x
-                // in his repo, that one is loaded instead, for which we still need this.
-                typescript: <any>{
-                    transpileOnly: true,
-                    compilerOptions: { sourceMap: true, inlineSourceMap: false }
-                }
-            }),
-            isFallbackConfig: true
-        };
+        try {
+            const sveltePreprocess = importSveltePreprocess(path);
+            Logger.log(
+                (foundConfig
+                    ? 'Found svelte.config.js but there was an error loading it. '
+                    : 'No svelte.config.js found. ') +
+                    'Using https://github.com/sveltejs/svelte-preprocess as fallback'
+            );
+            return {
+                preprocess: sveltePreprocess({
+                    // 4.x does not have transpileOnly anymore, but if the user has version 3.x
+                    // in his repo, that one is loaded instead, for which we still need this.
+                    typescript: {
+                        transpileOnly: true,
+                        compilerOptions: { sourceMap: true, inlineSourceMap: false }
+                    }
+                }),
+                isFallbackConfig: true
+            };
+        } catch (e) {
+            // User doesn't have svelte-preprocess installed, provide a barebones TS preprocessor
+            return {
+                preprocess: {
+                    // @ts-ignore name property exists in Svelte 4 onwards
+                    name: 'svelte-language-tools-ts-fallback-preprocessor',
+                    script: ({ content, attributes, filename }) => {
+                        if (attributes.lang !== 'ts') return;
+
+                        const { outputText, sourceMapText } = ts.transpileModule(content, {
+                            fileName: filename,
+                            compilerOptions: {
+                                module: ts.ModuleKind.ESNext,
+                                target: ts.ScriptTarget.ESNext,
+                                sourceMap: true,
+                                verbatimModuleSyntax: true
+                            }
+                        });
+                        return { code: outputText, map: sourceMapText };
+                    }
+                },
+                isFallbackConfig: true
+            };
+        }
     }
 }
 

packages/language-server/src/plugins/svelte/SvelteDocument.ts

@@ -37,6 +37,7 @@ type PositionMapper = Pick<DocumentMapper, 'getGeneratedPosition' | 'getOriginal
 export class SvelteDocument {
     private transpiledDoc: ITranspiledSvelteDocument | undefined;
     private compileResult: SvelteCompileResult | undefined;
+    private svelteVersion: [number, number] | undefined;
 
     public script: TagInformation | null;
     public moduleScript: TagInformation | null;
@@ -69,9 +70,11 @@ export class SvelteDocument {
 
     async getTranspiled(): Promise<ITranspiledSvelteDocument> {
         if (!this.transpiledDoc) {
-            const {
-                version: { major, minor }
-            } = getPackageInfo('svelte', this.getFilePath());
+            if (!this.svelteVersion) {
+                const { major, minor } = getPackageInfo('svelte', this.getFilePath()).version;
+                this.svelteVersion = [major, minor];
+            }
+            const [major, minor] = this.svelteVersion;
 
             if (major > 3 || (major === 3 && minor >= 32)) {
                 this.transpiledDoc = await TranspiledSvelteDocument.create(

packages/language-server/src/plugins/svelte/features/getDiagnostics.ts

@@ -1,5 +1,3 @@
-// @ts-ignore
-import { Warning } from 'svelte/types/compiler/interfaces';
 import {
     CancellationToken,
     Diagnostic,
@@ -63,6 +61,17 @@ async function tryGetDiagnostics(
         if (cancellationToken?.isCancellationRequested) {
             return [];
         }
+
+        let ignoreScriptWarnings = false;
+        let ignoreStyleWarnings = false;
+        let ignoreTemplateWarnings = false;
+        if (!document.config?.preprocess || !!document.config.isFallbackConfig) {
+            ignoreTemplateWarnings = !!document.getLanguageAttribute('template');
+            ignoreStyleWarnings = !!document.getLanguageAttribute('style');
+            const scriptAttr = document.getLanguageAttribute('script');
+            ignoreScriptWarnings = !!scriptAttr && scriptAttr !== 'ts';
+        }
+
         return (res.warnings || [])
             .filter((warning) => settings[warning.code] !== 'ignore')
             .map((warning) => {
@@ -81,7 +90,15 @@ async function tryGetDiagnostics(
             })
             .map((diag) => mapObjWithRangeToOriginal(transpiled, diag))
             .map((diag) => adjustMappings(diag, document))
-            .filter((diag) => isNoFalsePositive(diag, document));
+            .filter((diag) =>
+                isNoFalsePositive(
+                    diag,
+                    document,
+                    ignoreScriptWarnings,
+                    ignoreStyleWarnings,
+                    ignoreTemplateWarnings
+                )
+            );
     } catch (err) {
         return createParserErrorDiagnostic(err, document)
             .map((diag) => mapObjWithRangeToOriginal(transpiled, diag))
@@ -290,8 +307,28 @@ function getErrorMessage(error: any, source: string, hint = '') {
     );
 }
 
-function isNoFalsePositive(diag: Diagnostic, doc: Document): boolean {
-    if (diag.code !== 'unused-export-let') {
+function isNoFalsePositive(
+    diag: Diagnostic,
+    doc: Document,
+    ignoreScriptWarnings: boolean,
+    ignoreStyleWarnings: boolean,
+    ignoreTemplateWarnings: boolean
+): boolean {
+    if (
+        (ignoreTemplateWarnings || ignoreScriptWarnings) &&
+        (typeof diag.code !== 'string' || !diag.code.startsWith('a11y'))
+    ) {
+        return false;
+    }
+
+    if (
+        ignoreStyleWarnings &&
+        (diag.code === 'css-unused-selector' || diag.code === 'css_unused_selector')
+    ) {
+        return false;
+    }
+
+    if (diag.code !== 'unused-export-let' && diag.code !== 'export_let_unused') {
         return true;
     }
 
@@ -328,7 +365,7 @@ function adjustMappings(diag: Diagnostic, doc: Document): Diagnostic {
     diag.range = moveRangeStartToEndIfNecessary(diag.range);
 
     if (
-        diag.code === 'css-unused-selector' &&
+        (diag.code === 'css-unused-selector' || diag.code === 'css_unused_selector') &&
         doc.styleInfo &&
         !isInTag(diag.range.start, doc.styleInfo)
     ) {

packages/language-server/test/plugins/svelte/features/getDiagnostics.test.ts

@@ -31,7 +31,12 @@ describe('SveltePlugin#getDiagnostics', () => {
         docText?: string;
     }) {
         const document = new Document('', docText);
-        const svelteDoc: SvelteDocument = <any>{ getTranspiled, getCompiled, config };
+        const svelteDoc: SvelteDocument = <any>{
+            getTranspiled,
+            getCompiled,
+            config,
+            getSvelteVersion: () => [4, 0]
+        };
         const result = await getDiagnostics(document, svelteDoc, settings);
         return {
             toEqual: (expected: Diagnostic[]) => assert.deepStrictEqual(result, expected)
@@ -298,7 +303,9 @@ describe('SveltePlugin#getDiagnostics', () => {
                             }
                         ]
                     }),
-                config: {}
+                config: {
+                    preprocess: []
+                }
             })
         ).toEqual([
             {
@@ -343,7 +350,9 @@ describe('SveltePlugin#getDiagnostics', () => {
                             ]
                         }
                     }),
-                config: {}
+                config: {
+                    preprocess: []
+                }
             })
         ).toEqual([]);
     });
@@ -372,7 +381,9 @@ describe('SveltePlugin#getDiagnostics', () => {
                             ]
                         }
                     }),
-                config: {}
+                config: {
+                    preprocess: []
+                }
             })
         ).toEqual([]);
     });
@@ -399,7 +410,9 @@ describe('SveltePlugin#getDiagnostics', () => {
                             ]
                         }
                     }),
-                config: {},
+                config: {
+                    preprocess: []
+                },
                 settings: { 123: 'ignore' }
             })
         ).toEqual([]);
@@ -425,7 +438,9 @@ describe('SveltePlugin#getDiagnostics', () => {
                             }
                         ]
                     }),
-                config: {},
+                config: {
+                    preprocess: []
+                },
                 settings: { 123: 'error' }
             })
         ).toEqual([