Fix Swift formatter detection when version is main

## Summary:

Fixes #59598. Some Swift toolchains report `main` for `swift format --version`, so the formatter is skipped even when the toolchain meets the minimum version. When `swift format` reports `main`, check `swift --version` and use it to enforce the existing minimum version. Other formatter candidates still require a parseable formatter version.

## Changelog:

[INTERNAL] [FIXED] - Detect the Swift toolchain version when `swift format` reports `main`.

## Test Plan:

- Ran `NODE_PATH=/Volumes/SSD512/Work/mobile/force-mobile/node_modules /Volumes/SSD512/Work/mobile/force-mobile/node_modules/.bin/jest scripts/__tests__/format-swift-test.js --runInBand --config '{"rootDir":"/tmp/react-native-contribution","testEnvironment":"node","transform":{}}'`: 2 tests passed. The Swift 6.4 case failed before the change; the Swift 6.2 case remains rejected.
- Ran `git diff --check`: passed.
- Xcode 27.1 was not available for an end-to-end check. The test simulates its reported version output. Full repository checks were not run.

Differential Revision: D128394284

Pull Request resolved: #59623

Author: LuisPeixoto

scripts/__tests__/format-swift-test.js

@@ -0,0 +1,63 @@
+/**
+ * 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.
+ *
+ * @noflow
+ * @format
+ */
+
+'use strict';
+
+jest.mock('../format-utils', () => ({
+  IS_META_CHECKOUT: false,
+  commandVersion: jest.fn(),
+  findMetaTool: jest.fn(() => null),
+}));
+jest.mock('tinyglobby', () => ({globSync: jest.fn(() => [])}));
+
+const originalSwiftFormat = process.env.SWIFT_FORMAT;
+
+beforeEach(() => {
+  delete process.env.SWIFT_FORMAT;
+});
+
+afterEach(() => {
+  if (originalSwiftFormat === undefined) {
+    delete process.env.SWIFT_FORMAT;
+  } else {
+    process.env.SWIFT_FORMAT = originalSwiftFormat;
+  }
+  jest.resetModules();
+  jest.clearAllMocks();
+  jest.restoreAllMocks();
+});
+
+test.each([
+  ['6.4', true],
+  ['6.2', false],
+])(
+  'checks the Swift toolchain version when the formatter reports main (%s)',
+  (version, accepted) => {
+    const {commandVersion} = require('../format-utils');
+    const {globSync} = require('tinyglobby');
+    commandVersion.mockImplementation((command, args) => {
+      if (command === 'swift' && args?.[0] === 'format') {
+        return {status: 0, output: 'main'};
+      }
+      if (command === 'swift') {
+        return {
+          status: 0,
+          output: `Apple Swift version ${version} (swiftlang)`,
+        };
+      }
+      return {status: 1, output: ''};
+    });
+    jest.spyOn(console, 'warn').mockImplementation(() => {});
+
+    require('../format-swift');
+
+    expect(globSync).toHaveBeenCalledTimes(accepted ? 1 : 0);
+  },
+);

scripts/format-swift.js

@@ -81,7 +81,20 @@ function findSwiftFormat() {
   }
   for (const [command, prefixArguments] of candidates) {
     const result = commandVersion(command, prefixArguments);
-    const version = parseSwiftFormatVersion(result.output);
+    let version = parseSwiftFormatVersion(result.output);
+    if (
+      result.status === 0 &&
+      version == null &&
+      result.output.trim() === 'main' &&
+      command === 'swift' &&
+      prefixArguments.length === 1 &&
+      prefixArguments[0] === 'format'
+    ) {
+      const toolchain = commandVersion(command);
+      if (toolchain.status === 0) {
+        version = parseSwiftFormatVersion(toolchain.output);
+      }
+    }
     if (
       result.status === 0 &&
       version != null &&