Add pre-transform that replaces nullable types with undefined for object types

scripts/build/build-types/transforms/__tests__/replaceNullablePropertiesWithUndefined-test.js

@@ -0,0 +1,59 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+const replaceNullablePropertiesWithUndefined = require('../replaceNullablePropertiesWithUndefined.js');
+const {parse, print} = require('hermes-transform');
+
+const prettierOptions = {parser: 'babel'};
+
+async function translate(code: string): Promise<string> {
+  const parsed = await parse(code);
+  const result = await replaceNullablePropertiesWithUndefined(parsed);
+  return print(result.ast, result.mutatedCode, prettierOptions);
+}
+
+describe('replaceNullablePropertiesWithUndefined', () => {
+  test('should not replace nullable with undefined outside object type definition', async () => {
+    const code = `function foo(arg: ?string) {}`;
+    const result = await translate(code);
+    expect(result).toMatchInlineSnapshot(`
+      "function foo(arg: ?string) {}
+      "
+    `);
+  });
+
+  test('should replace nullable with undefined inside object type definition', async () => {
+    const code = `type Foo = {bar: ?string};`;
+    const result = await translate(code);
+    expect(result).toMatchInlineSnapshot(`
+      "type Foo = { bar: string | undefined };
+      "
+    `);
+  });
+
+  test('should replace nullable with undefined inside nested object type definition', async () => {
+    const code = `type Foo = {bar: {baz: ?string}};`;
+    const result = await translate(code);
+    expect(result).toMatchInlineSnapshot(`
+      "type Foo = { bar: { baz: string | undefined } };
+      "
+    `);
+  });
+
+  test('should replace nullable with undefined in function inside object type definition', async () => {
+    const code = `type Foo = {bar: (?string) => void};`;
+    const result = await translate(code);
+    expect(result).toMatchInlineSnapshot(`
+      "type Foo = { bar: (string | undefined) => void };
+      "
+    `);
+  });
+});

scripts/build/build-types/transforms/replaceNullablePropertiesWithUndefined.js

@@ -0,0 +1,62 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+import type {ESNode, TypeAnnotationType} from 'hermes-estree';
+import type {TransformVisitor} from 'hermes-transform';
+import type {ParseResult} from 'hermes-transform/dist/transform/parse';
+import type {TransformASTResult} from 'hermes-transform/dist/transform/transformAST';
+
+const {transformAST} = require('hermes-transform/dist/transform/transformAST');
+
+function isInsideObjectTypeProperty(node: TypeAnnotationType) {
+  let current: ESNode = node;
+  while (current) {
+    if (current.type === 'ObjectTypeProperty') {
+      return true;
+    }
+    current = current.parent;
+  }
+  return false;
+}
+
+const visitors: TransformVisitor = context => ({
+  NullableTypeAnnotation(node): void {
+    if (!isInsideObjectTypeProperty(node)) {
+      return;
+    }
+
+    // $FlowExpectedError[incompatible-call] - UnionTypeAnnotation is not assignable to NullableTypeAnnotation
+    context.replaceNode(node, {
+      type: 'UnionTypeAnnotation',
+      types: [
+        node.typeAnnotation,
+        {
+          type: 'GenericTypeAnnotation',
+          id: {
+            type: 'Identifier',
+            name: 'undefined',
+          },
+        },
+      ],
+    });
+  },
+});
+
+/**
+ * Replaces all Stringish type references with string
+ */
+async function replaceNullablePropertiesWithUndefined(
+  source: ParseResult,
+): Promise<TransformASTResult> {
+  return transformAST(source, visitors);
+}
+
+module.exports = replaceNullablePropertiesWithUndefined;

scripts/build/build-types/translateSourceFile.js

@@ -25,6 +25,7 @@ const preTransforms: Array<PreTransformFn> = [
   require('./transforms/replaceRequiresWithImports'),
   require('./transforms/replaceEmptyWithNever'),
   require('./transforms/replaceStringishWithString'),
+  require('./transforms/replaceNullablePropertiesWithUndefined'),
 ];
 const postTransforms: Array<PluginObj<mixed>> = [];
 const prettierOptions = {parser: 'babel'};