RN: Enforce flow-typed Signatures

Summary:
Creates a new `valid-flow-typed-signature` ESLint rule that validates the `flow-typed` signatures at the top of each file.

This lint rule will discourage contributors from locally forking the `flow-typed` definitions. Instead, any changes should be submitted as patches to the upstream definition in: https://github.com/flow-typed/flow-typed

Changelog:
[Internal]

Reviewed By: rickhanlonii

Differential Revision: D39868721

fbshipit-source-id: e5e3ffe7568dbe52c9b598b53110b0fcbcad3e38

.eslintignore

@@ -2,7 +2,6 @@
 **/staticBundle.js
 docs/generatedComponentApiDocs.js
 flow/
-flow-typed/
 Libraries/Renderer/*
 Libraries/vendor/**/*
 node_modules/

.eslintrc.js

@@ -49,6 +49,8 @@ module.exports = {
     {
       files: ['flow-typed/**/*.js'],
       rules: {
+        'lint/valid-flow-typed-signature': 2,
+        'no-unused-vars': 0,
         quotes: 0,
       },
     },

tools/eslint/rules/__tests__/valid-flow-typed-signature-test.js

@@ -0,0 +1,48 @@
+/**
+ * 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.
+ *
+ * @format
+ */
+
+'use strict';
+
+const rule = require('../valid-flow-typed-signature.js');
+const {RuleTester} = require('eslint');
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('hermes-eslint'),
+  parserOptions: {
+    ecmaVersion: 6,
+    sourceType: 'module',
+  },
+});
+
+ruleTester.run('valid-flow-typed-signature', rule, {
+  valid: [
+    {
+      code: `// ...`,
+    },
+    {
+      code: [
+        `// flow-typed signature: 9333721862f426d869c32ea6f7cecfda`,
+        `// flow-typed version: 123456/xyz_v1.x.x/flow_>=v0.83.x`,
+        ``,
+        `declare module "xyz" {}`,
+      ].join('\n'),
+    },
+  ],
+  invalid: [
+    {
+      code: [
+        `// flow-typed signature: 90affbd9a1954ec9ff029b7ad7183a16`,
+        `// flow-typed version: 123456/xyz_v1.x.x/flow_>=v0.83.x`,
+        ``,
+        `declare module "xyz" {}`,
+      ].join('\n'),
+      errors: [{messageId: 'invalidSignature'}],
+    },
+  ],
+});

tools/eslint/rules/valid-flow-typed-signature.js

@@ -0,0 +1,71 @@
+/**
+ * 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.
+ *
+ * @format
+ */
+
+'use strict';
+
+const crypto = require('node:crypto');
+
+// @see https://github.com/flow-typed/flow-typed
+const HASH_COMMENT_RE = /\/\/ flow-typed signature: (.*)$/;
+
+module.exports = {
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'Require valid flow-typed signatures',
+      recommended: true,
+    },
+    messages: {
+      invalidSignature:
+        'Invalid flow-typed signature; avoid local modifications',
+    },
+    schema: [],
+  },
+
+  create(context) {
+    return {
+      Program() {
+        const sourceText = context.getSourceCode().getText();
+
+        const firstLineEndIndex = sourceText.indexOf('\n');
+        const firstLine = sourceText.substr(0, firstLineEndIndex);
+
+        const match = firstLine.match(HASH_COMMENT_RE);
+        if (match == null) {
+          // Not a signed flow-typed definition file.
+          return;
+        }
+
+        const hash = match[1];
+        const versionedCode = sourceText.substr(firstLineEndIndex + 1);
+        if (md5(versionedCode) === hash) {
+          return;
+        }
+
+        context.report({
+          loc: {
+            start: {
+              line: 1,
+              column: firstLine.length - hash.length,
+            },
+            end: {
+              line: 1,
+              column: firstLine.length,
+            },
+          },
+          messageId: 'invalidSignature',
+        });
+      },
+    };
+  },
+};
+
+function md5(string) {
+  return crypto.createHash('md5').update(string).digest('hex');
+}