Fix name minifying (#10252)

Author: timotheeguerin

.chronus/changes/fix-bundler-name-minify-2026-3-2-18-14-15.md

@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: fix
+packages:
+  - "@typespec/bundler"
+---
+
+Fix name minifying

packages/bundler/src/bundler.ts

@@ -239,6 +239,7 @@ async function createEsBuildContext(
     format: "esm",
     target: "es2024",
     minify,
+    keepNames: minify,
     plugins: [virtualPlugin, nodeModulesPolyfillPlugin({}), ...plugins],
   });
 }

packages/bundler/test/test.test.ts

@@ -1,8 +1,54 @@
-import { ok } from "assert";
-import { describe, it } from "vitest";
+import { mkdtemp, rm, writeFile } from "fs/promises";
+import { tmpdir } from "os";
+import { join } from "path";
+import { describe, expect, it } from "vitest";
+import { createTypeSpecBundle } from "../src/bundler.js";
 
 describe("bundler", () => {
-  it("works", () => {
-    ok(true);
+  /**
+   * Regression test: TypeSpec decorator functions are identified by their `.name` property
+   * at runtime (e.g., `d.decorator.name === "$armResourceOperations"`).
+   * When esbuild minifies library bundles, it can rename functions, changing their `.name`.
+   * The bundler must use `keepNames: true` to preserve function names in minified output.
+   */
+  it("preserves function names when minifying", async () => {
+    const tmpDir = await mkdtemp(join(tmpdir(), "typespec-bundler-test-"));
+    try {
+      // Create a minimal TypeSpec library with named decorator function exports
+      await writeFile(
+        join(tmpDir, "package.json"),
+        JSON.stringify({
+          name: "test-lib",
+          version: "1.0.0",
+          main: "index.js",
+          tspMain: "main.tsp",
+          peerDependencies: {},
+        }),
+      );
+      await writeFile(
+        join(tmpDir, "main.tsp"),
+        ['import "./index.js";', "namespace TestLib;"].join("\n"),
+      );
+      await writeFile(
+        join(tmpDir, "index.js"),
+        [
+          "export function $testDecorator(context, target) { }",
+          "export function $anotherDecorator(context, target) { }",
+        ].join("\n"),
+      );
+
+      const bundle = await createTypeSpecBundle(tmpDir, { minify: true });
+      const indexFile = bundle.files.find((f) => f.filename === "index.js");
+      expect(indexFile, "index.js should be in bundle output").toBeDefined();
+
+      // The bundle's jsSourceFiles should contain modules where the function
+      // .name property is preserved. With keepNames, esbuild emits a helper
+      // that restores the original name via Object.defineProperty.
+      // We verify the original function names appear as string literals in the output.
+      expect(indexFile!.content).toContain('"$testDecorator"');
+      expect(indexFile!.content).toContain('"$anotherDecorator"');
+    } finally {
+      await rm(tmpDir, { recursive: true });
+    }
   });
 });