support nesting typekits (microsoft#7108)

Fixes microsoft#7094

The caveat to this change is that you shouldn't have typekits that use
regular fields.

For example - `$.foo.type` <-- if this is a regular field that contains
an object, then that object will be wrapped in a Proxy, breaking object
identity.

However, we follow the pattern of using `get` descriptors for this
use-case instead, which would not break object identity.

---------

Co-authored-by: Christopher Radek <Christopher.Radek@microsoft.com>

Author: chrisradek

.chronus/changes/tk-nested-ns-2025-3-23-16-4-8.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/compiler"
+---
+
+Adds support for nesting typekits

packages/compiler/src/experimental/typekit/index.ts

@@ -1,6 +1,6 @@
 import type { Program } from "../../core/program.js";
 import { Realm } from "../realm.js";
-import { Typekit, TypekitNamespaceSymbol, TypekitPrototype } from "./define-kit.js";
+import { Typekit, TypekitPrototype } from "./define-kit.js";
 
 export * from "./create-diagnosable.js";
 export * from "./define-kit.js";
@@ -65,9 +65,13 @@ export function createTypekit(realm: Realm): Typekit {
         return proxyWrapper;
       }
 
-      // Only wrap objects marked as Typekit namespaces
-      if (typeof value === "object" && value !== null && isTypekitNamespace(value)) {
-        return new Proxy(value, handler); // Wrap namespace objects
+      // Wrap objects to ensure their functions are bound correctly, avoid wrapping `get` accessors
+      if (
+        typeof value === "object" &&
+        value !== null &&
+        !Reflect.getOwnPropertyDescriptor(target, prop)?.get
+      ) {
+        return new Proxy(value, handler);
       }
 
       return value;
@@ -78,11 +82,6 @@ export function createTypekit(realm: Realm): Typekit {
   return proxy;
 }
 
-// Helper function to check if an object is a Typekit namespace
-function isTypekitNamespace(obj: any): boolean {
-  return obj && !!obj[TypekitNamespaceSymbol];
-}
-
 // #region Default Typekit
 
 const DEFAULT_REALM = Symbol.for("TypeSpec.Typekit.DEFAULT_TYPEKIT_REALM");

packages/compiler/test/experimental/typekit/define-kit.test.ts

@@ -12,3 +12,30 @@ it("can define a kit", async () => {
 
   expect(($(program) as any).test()).toBe(true);
 });
+
+it("supports nested kits", async () => {
+  const { program } = await createContextMock();
+  defineKit({
+    __nestedTest: {
+      get foo() {
+        return this.program.checker.anyType;
+      },
+      nested: {
+        get foo() {
+          return this.program.checker.anyType;
+        },
+        bar() {
+          return this.program.checker.anyType;
+        },
+      } as any,
+    } as any,
+  });
+  const tk = $(program);
+
+  // Ensure program isn't wrapped in a proxy
+  expect(tk.program).toBe(program);
+
+  expect((tk as any).__nestedTest.foo).toBe(program.checker.anyType);
+  expect((tk as any).__nestedTest.nested.foo).toBe(program.checker.anyType);
+  expect((tk as any).__nestedTest.nested.bar()).toBe(program.checker.anyType);
+});