[6.x] [core/public/deepFreeze] fix recursive type for better array su…

…pport (#22904) (#22932)

Backports the following commits to 6.x:
 - [core/public/deepFreeze] fix recursive type for better array support  (#22904)

src/core/public/injected_metadata/__fixtures__/frozen_object_mutation.ts → src/core/public/injected_metadata/__fixtures__/frozen_object_mutation/index.ts

@@ -17,17 +17,34 @@
  * under the License.
  */
 
-import { deepFreeze } from '../deep_freeze';
+import { deepFreeze } from '../../deep_freeze';
 
-const obj = deepFreeze({
-  foo: {
-    bar: {
-      baz: 1,
+deepFreeze(
+  {
+    foo: {
+      bar: {
+        baz: 1,
+      },
     },
-  },
-});
+  }
+).foo.bar.baz = 2;
 
-delete obj.foo;
-obj.foo = 1;
-obj.foo.bar.baz = 2;
-obj.foo.bar.box = false;
+deepFreeze(
+  {
+    foo: [
+      {
+        bar: 1,
+      },
+    ],
+  }
+).foo[0].bar = 2;
+
+deepFreeze(
+  {
+    foo: [1],
+  }
+).foo[0] = 2;
+
+deepFreeze({
+  foo: [1],
+}).foo.push(2);

src/core/public/injected_metadata/__fixtures__/frozen_object_mutation.tsconfig.json → src/core/public/injected_metadata/__fixtures__/frozen_object_mutation/tsconfig.json

@@ -6,8 +6,7 @@
       "esnext"
     ]
   },
-  "include": [
-    "frozen_object_mutation.ts",
-    "../deep_freeze.ts"
+  "files": [
+    "index.ts"
   ]
 }

src/core/public/injected_metadata/deep_freeze.test.ts

@@ -75,28 +75,17 @@ it('prevents reassigning items in a frozen array', () => {
 });
 
 it('types return values to prevent mutations in typescript', async () => {
-  const result = await execa.stdout(
-    'tsc',
-    [
-      '--noEmit',
-      '--project',
-      resolve(__dirname, '__fixtures__/frozen_object_mutation.tsconfig.json'),
-    ],
-    {
-      cwd: resolve(__dirname, '__fixtures__'),
-      reject: false,
-    }
-  );
+  await expect(
+    execa.stdout('tsc', ['--noEmit'], {
+      cwd: resolve(__dirname, '__fixtures__/frozen_object_mutation'),
+    })
+  ).rejects.toThrowErrorMatchingInlineSnapshot(`
+"Command failed: tsc --noEmit
 
-  const errorCodeRe = /\serror\s(TS\d{4}):/g;
-  const errorCodes = [];
-  while (true) {
-    const match = errorCodeRe.exec(result);
-    if (!match) {
-      break;
-    }
-    errorCodes.push(match[1]);
-  }
-
-  expect(errorCodes).toEqual(['TS2704', 'TS2540', 'TS2540', 'TS2339']);
+index.ts(30,11): error TS2540: Cannot assign to 'baz' because it is a constant or a read-only property.
+index.ts(40,10): error TS2540: Cannot assign to 'bar' because it is a constant or a read-only property.
+index.ts(42,1): error TS2542: Index signature in type 'RecursiveReadonlyArray<number>' only permits reading.
+index.ts(50,8): error TS2339: Property 'push' does not exist on type 'RecursiveReadonlyArray<number>'.
+"
+`);
 });

src/core/public/injected_metadata/deep_freeze.ts

@@ -19,9 +19,12 @@
 
 type Freezable = { [k: string]: any } | any[];
 
-type RecursiveReadOnly<T> = T extends Freezable
-  ? Readonly<{ [K in keyof T]: RecursiveReadOnly<T[K]> }>
-  : T;
+// if we define this inside RecursiveReadonly TypeScript complains
+interface RecursiveReadonlyArray<T> extends ReadonlyArray<RecursiveReadonly<T>> {}
+
+type RecursiveReadonly<T> = T extends any[]
+  ? RecursiveReadonlyArray<T[number]>
+  : T extends object ? Readonly<{ [K in keyof T]: RecursiveReadonly<T[K]> }> : T;
 
 export function deepFreeze<T extends Freezable>(object: T) {
   // for any properties that reference an object, makes sure that object is
@@ -32,5 +35,5 @@ export function deepFreeze<T extends Freezable>(object: T) {
     }
   }
 
-  return Object.freeze(object) as RecursiveReadOnly<T>;
+  return Object.freeze(object) as RecursiveReadonly<T>;
 }