fix(transforms): classify TypeScript references in the server-exports strip

extensions/ext-parser-babel/src/parser-only.test.ts

@@ -28,6 +28,30 @@ describe("BabelParseOnlyParser", () => {
     assertEquals(decorated.type, "File");
   });
 
+  it("parses compiled JSX under a Markdown or MDX path", async () => {
+    // Markdown and MDX reach the parser as compiled JSX. Choosing the Babel
+    // plugins from the authored extension would leave JSX off and the markup
+    // would parse as a regular expression.
+    const compiled = "export default function MDXContent() { return <h1>Title</h1>; }";
+
+    const parsed = await Promise.all(
+      ["page.mdx", "page.md", "page.MDX"].map((filePath) =>
+        parser.parse({ code: compiled, filePath })
+      ),
+    );
+
+    assertEquals(parsed.map((ast) => ast.type), ["File", "File", "File"]);
+  });
+
+  it("keeps `<T>x` a type assertion for a `.ts` path", async () => {
+    const asserted = await parser.parse({
+      code: "const value = <string> input;",
+      filePath: "module.ts",
+    });
+
+    assertEquals(asserted.type, "File");
+  });
+
   it("preserves Babel syntax-error identity and location metadata", async () => {
     let thrown: unknown;
     try {

extensions/ext-parser-babel/src/parser-only.ts

@@ -18,6 +18,21 @@ export interface BabelParseOnlyParserContract {
   parse(options: ParseOptions): Promise<ASTNode>;
 }
 
+/**
+ * The path the plugin choice reasons about.
+ *
+ * Markdown and MDX can reach this parser as compiled JSX, and the authored
+ * `.md` or `.mdx` extension would switch JSX off, so the emitted markup parses
+ * as a regular expression and throws "Unterminated regular expression". Map
+ * them onto a `.tsx` path for the plugin choice only. Nothing else reads this
+ * value, and `.ts` keeps `<T>x` a type assertion because only Markdown paths
+ * are rewritten.
+ */
+function parseablePath(filePath?: string): string | undefined {
+  if (filePath === undefined) return undefined;
+  return filePath.replace(/\.mdx?$/i, ".tsx");
+}
+
 function pickPlugins(filePath?: string): parser.ParserPlugin[] {
   const normalizedPath = filePath?.toLowerCase() ?? "";
   const supportsJsx = !filePath ||
@@ -53,7 +68,7 @@ export class BabelParseOnlyParser implements BabelParseOnlyParserContract {
       sourceType: "unambiguous",
       allowReturnOutsideFunction: options.allowReturnOutsideFunction === true ||
         /\.(?:cjs|js)$/.test(filePath),
-      plugins: pickPlugins(options.filePath),
+      plugins: pickPlugins(parseablePath(options.filePath)),
     });
     const node: { type: string } = ast;
     return Promise.resolve(node as ASTNode);