fix: Clear outDir if set in tsconfig (#406)

* Clear outDir if set in tsconfig

If outDir is set, Typescript sets directories in the source maps relative to it
which causes problems in `concatSourceMaps` when the paths in the source
point to nonexistent files instead of the virtual modules set up by the
transformer.

Fixes #405

* Unconditionally clear `outDir`

Author: dimfeld

Diff for: src/transformers/typescript.ts

@@ -270,6 +270,8 @@ function getCompilerOptions({
     ...(convertedCompilerOptions as CompilerOptions),
     importsNotUsedAsValues: ts.ImportsNotUsedAsValues.Error,
     allowNonTsExtensions: true,
+    // Clear outDir since it causes source map issues when the files aren't actually written to disk.
+    outDir: undefined,
   };
 
   if (

Diff for: test/fixtures/tsconfig.outdir.json

@@ -0,0 +1,7 @@
+{
+  "compilerOptions": {
+    "module": "es2015",
+    "skipLibCheck": true,
+    "outDir": "dist"
+  }
+}

Diff for: test/transformers/typescript.test.ts

@@ -177,6 +177,20 @@ describe('transformer - typescript', () => {
       expect(map).toHaveProperty('sources', ['App.svelte']);
     });
 
+    it('should work when tsconfig contains outDir', async () => {
+      const opts = sveltePreprocess({
+        typescript: {
+          tsconfigFile: './test/fixtures/tsconfig.outdir.json',
+          handleMixedImports: true,
+        },
+        sourceMap: true,
+      });
+
+      const preprocessed = await preprocess(template, opts);
+
+      expect(preprocessed.toString?.()).toContain(EXPECTED_SCRIPT);
+    });
+
     it('supports extends field', () => {
       const { options } = loadTsconfig({}, getTestAppFilename(), {
         tsconfigFile: './test/fixtures/tsconfig.extends1.json',