chore: support function for compilerOptions

For svelte2tsx we gotta make a compromise - since everything has to be sync, we can only pass the unpreprocessed file. Should be fine in practise because a preprocessor influencing the code in such a way that it in turn influences the compiler options is probably vanishingly rare.

sveltejs/svelte#12415

Author: dummdidumm

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

@@ -23,7 +23,9 @@ export type InternalPreprocessorGroup = PreprocessorGroup & {
 };
 
 export interface SvelteConfig {
-    compilerOptions?: CompileOptions;
+    compilerOptions?:
+        | CompileOptions
+        | ((input: { filename: string; code: string }) => CompileOptions);
     preprocess?: InternalPreprocessorGroup | InternalPreprocessorGroup[];
     loadConfigError?: any;
     isFallbackConfig?: boolean;

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

@@ -98,9 +98,15 @@ export class SvelteDocument {
         return this.compileResult;
     }
 
-    async getCompiledWith(options: CompileOptions = {}): Promise<SvelteCompileResult> {
+    async getCompiledWith(options: SvelteConfig['compilerOptions']): Promise<SvelteCompileResult> {
         const svelte = importSvelte(this.getFilePath());
-        return svelte.compile((await this.getTranspiled()).getText(), options);
+        const code = (await this.getTranspiled()).getText();
+        return svelte.compile(
+            code,
+            typeof options === 'function'
+                ? options({ filename: this.getFilePath(), code })
+                : (options ?? {})
+        );
     }
 
     private getSvelteVersion() {

packages/language-server/src/plugins/typescript/DocumentSnapshot.ts

@@ -200,6 +200,16 @@ function preprocessSvelteFile(document: Document, options: SvelteSnapshotOptions
         : ts.ScriptKind.JS;
 
     try {
+        const compilerOptions =
+            typeof document.config?.compilerOptions === 'function'
+                ? document.config.compilerOptions({
+                      filename: document.getFilePath() ?? '',
+                      // Ideally we could pass the preprocessed text here, but we have to be synchronous here
+                      // and the preprocessed text is only available asynchronously. Most people will only
+                      // branch on filename anyway.
+                      code: text
+                  })
+                : document.config?.compilerOptions;
         const tsx = svelte2tsx(text, {
             parse: options.parse,
             version: options.version,
@@ -208,10 +218,8 @@ function preprocessSvelteFile(document: Document, options: SvelteSnapshotOptions
             mode: 'ts',
             typingsNamespace: options.typingsNamespace,
             emitOnTemplateError: options.transformOnTemplateError,
-            namespace: document.config?.compilerOptions?.namespace,
-            accessors:
-                document.config?.compilerOptions?.accessors ??
-                document.config?.compilerOptions?.customElement
+            namespace: compilerOptions?.namespace,
+            accessors: compilerOptions?.accessors ?? compilerOptions?.customElement
         });
         text = tsx.code;
         tsxMap = tsx.map as EncodedSourceMap;