chore: Extract codegen case 'Stringish' into a single emitStringish function (#34936)

Summary:
This PR extracts the content of the codegen case `'Stringish'` into a single `emitStringish` function inside the `parsers-primitives.js` file and uses it in both Flow and TypeScript parsers as requested on https://github.com/facebook/react-native/issues/34872. This also adds unit tests to the new `emitStringish` function.

## Changelog

[Internal] [Changed] - Extract the content of the case 'Stringish' into a single emitStringish function

Pull Request resolved: https://github.com/facebook/react-native/pull/34936

Test Plan:
Run `yarn jest react-native-codegen` and ensure CI is green

![image](https://user-images.githubusercontent.com/11707729/194987664-b588b82b-a9e0-49a9-a3cc-a03cb0a230e6.png)

Reviewed By: cipolleschi

Differential Revision: D40255921

Pulled By: rshest

fbshipit-source-id: 9c08f81f12c93995bb6ba032fabcd6451b8dc7c1

packages/react-native-codegen/src/parsers/__tests__/parsers-primitives-test.js

@@ -20,6 +20,7 @@ const {
   emitPromise,
   emitRootTag,
   emitVoid,
+  emitStringish,
   typeAliasResolution,
 } = require('../parsers-primitives.js');
 
@@ -127,6 +128,33 @@ describe('emitRootTag', () => {
   });
 });
 
+describe('emitStringish', () => {
+  describe('when nullable is true', () => {
+    it('returns nullable type annotation', () => {
+      const result = emitStringish(true);
+      const expected = {
+        type: 'NullableTypeAnnotation',
+        typeAnnotation: {
+          type: 'StringTypeAnnotation',
+        },
+      };
+
+      expect(result).toEqual(expected);
+    });
+  });
+
+  describe('when nullable is false', () => {
+    it('returns non nullable type annotation', () => {
+      const result = emitStringish(false);
+      const expected = {
+        type: 'StringTypeAnnotation',
+      };
+
+      expect(result).toEqual(expected);
+    });
+  });
+});
+
 describe('emitDouble', () => {
   describe('when nullable is true', () => {
     it('returns nullable type annotation', () => {

packages/react-native-codegen/src/parsers/flow/modules/index.js

@@ -46,6 +46,7 @@ const {
   emitPromise,
   emitRootTag,
   emitVoid,
+  emitStringish,
   typeAliasResolution,
 } = require('../../parsers-primitives');
 const {
@@ -203,9 +204,7 @@ function translateTypeAnnotation(
           return wrapNullable(nullable || isParamNullable, paramType);
         }
         case 'Stringish': {
-          return wrapNullable(nullable, {
+          return emitStringish(nullable);
-            type: 'StringTypeAnnotation',
-          });
         }
         case 'Int32': {
           return emitInt32(nullable);

packages/react-native-codegen/src/parsers/parsers-primitives.js

@@ -24,6 +24,7 @@ import type {
   ObjectTypeAnnotation,
   NativeModulePromiseTypeAnnotation,
   VoidTypeAnnotation,
+  StringTypeAnnotation,
 } from '../CodegenSchema';
 import type {ParserType} from './errors';
 import type {TypeAliasResolutionStatus} from './utils';
@@ -72,6 +73,12 @@ function emitVoid(nullable: boolean): Nullable<VoidTypeAnnotation> {
   });
 }
 
+function emitStringish(nullable: boolean): Nullable<StringTypeAnnotation> {
+  return wrapNullable(nullable, {
+    type: 'StringTypeAnnotation',
+  });
+}
+
 function typeAliasResolution(
   typeAliasResolutionStatus: TypeAliasResolutionStatus,
   objectTypeAnnotation: ObjectTypeAnnotation<
@@ -160,5 +167,6 @@ module.exports = {
   emitPromise,
   emitRootTag,
   emitVoid,
+  emitStringish,
   typeAliasResolution,
 };

packages/react-native-codegen/src/parsers/typescript/modules/index.js

@@ -46,6 +46,7 @@ const {
   emitPromise,
   emitRootTag,
   emitVoid,
+  emitStringish,
   typeAliasResolution,
 } = require('../../parsers-primitives');
 const {
@@ -236,9 +237,7 @@ function translateTypeAnnotation(
           );
         }
         case 'Stringish': {
-          return wrapNullable(nullable, {
+          return emitStringish(nullable);
-            type: 'StringTypeAnnotation',
-          });
         }
         case 'Int32': {
           return emitInt32(nullable);