Create a transform for sorting types inside a union (#50468)

Summary:
Pull Request resolved: #50468

Changelog: [Internal]

Reviewed By: huntie

Differential Revision: D72381049

fbshipit-source-id: 9b72f6617b8ac090be9bfd3503d66d89bb701029

Author: j-piasecki

scripts/build/build-types/transforms/__fixtures__/sortUnions.d.ts

@@ -0,0 +1,19 @@
+/**
+ * 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.
+ */
+
+type AFoo = unknown;
+type BFoo = unknown;
+type CFoo = unknown;
+type DFoo = unknown;
+
+type A = string | number;
+type B = DFoo | CFoo | BFoo | AFoo;
+type C = AFoo | BFoo | CFoo | DFoo;
+type D = BFoo | string | number | BFoo;
+type E = string | number | BFoo | AFoo | { foo: string } | { bar: string };
+type F = "D" | "C" | "B" | "A";
+type G = 3 | 2 | 1 | 0 | "D" | "C" | "B" | "A";

scripts/build/build-types/transforms/__tests__/__snapshots__/sortUnions-test.js.snap

@@ -0,0 +1,26 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`sortUnions should sort union members 1`] = `
+"/**
+ * 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.
+ */
+
+type AFoo = unknown;
+type BFoo = unknown;
+type CFoo = unknown;
+type DFoo = unknown;
+type A = number | string;
+type B = AFoo | BFoo | CFoo | DFoo;
+type C = AFoo | BFoo | CFoo | DFoo;
+type D = BFoo | BFoo | number | string;
+type E = AFoo | BFoo | number | string | {
+  bar: string;
+} | {
+  foo: string;
+};
+type F = \\"A\\" | \\"B\\" | \\"C\\" | \\"D\\";
+type G = \\"A\\" | \\"B\\" | \\"C\\" | \\"D\\" | 0 | 1 | 2 | 3;"
+`;

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

@@ -0,0 +1,34 @@
+/**
+ * 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 sortUnionsVisitor = require('../sortUnions.js');
+const babel = require('@babel/core');
+const {promises: fs} = require('fs');
+const path = require('path');
+
+async function translate(code: string): Promise<string> {
+  const result = await babel.transformAsync(code, {
+    plugins: ['@babel/plugin-syntax-typescript', sortUnionsVisitor],
+  });
+
+  return result.code;
+}
+
+describe('sortUnions', () => {
+  test('should sort union members', async () => {
+    const code = await fs.readFile(
+      path.join(__dirname, '../__fixtures__/sortUnions.d.ts'),
+      'utf-8',
+    );
+    const result = await translate(code);
+    expect(result).toMatchSnapshot();
+  });
+});

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

@@ -0,0 +1,38 @@
+/**
+ * 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 {PluginObj} from '@babel/core';
+
+import generate from '@babel/generator';
+import * as t from '@babel/types';
+
+const visitor: PluginObj<mixed> = {
+  visitor: {
+    TSUnionType(path) {
+      path.node.types.sort((a, b) => {
+        // push literal types to the end of the union
+        if (t.isTSTypeLiteral(a) && !t.isTSTypeLiteral(b)) {
+          return 1;
+        } else if (!t.isTSTypeLiteral(a) && t.isTSTypeLiteral(b)) {
+          return -1;
+        }
+
+        // get string representation of the types to correctly handle literals
+        const aString = generate(a).code;
+        const bString = generate(b).code;
+
+        return aString.localeCompare(bString);
+      });
+    },
+  },
+};
+
+module.exports = visitor;