[compiler] Init react-mcp-server (facebook#32859)

Just trying this out as a small hack for fun. Nothing serious is
planned.

Inits an MCP server that has 1 assistant prompt and two capabilities.

Author: poteto

compiler/packages/react-mcp-server/README.md

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+# React MCP Server (experimental)
+
+An experimental MCP Server for React.
+
+## Development
+
+First, add this file if you're using Claude Desktop: `code ~/Library/Application\ Support/Claude/claude_desktop_config.json`. Copy the absolute path from `which node` and from `react/compiler/react-mcp-server/dist/index.js` and paste, for example:
+
+```json
+{
+  "mcpServers": {
+    "react": {
+      "command": "/Users/<username>/.asdf/shims/node",
+      "args": [
+        "/Users/<username>/code/react/compiler/packages/react-mcp-server/dist/index.js"
+      ]
+    }
+  }
+}
+```
+
+Next, run `yarn workspace react-mcp-server watch` from the `react/compiler` directory and make changes as needed. You will need to restart Claude everytime you want to try your changes.

compiler/packages/react-mcp-server/package.json

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+{
+  "name": "react-mcp-server",
+  "version": "0.0.0",
+  "description": "React MCP Server (experimental)",
+  "bin": {
+    "react-mcp-server": "./dist/index.js"
+  },
+  "scripts": {
+    "build": "rimraf dist && tsup",
+    "test": "echo 'no tests'",
+    "watch": "yarn build --watch"
+  },
+  "dependencies": {
+    "@babel/core": "^7.26.0",
+    "@babel/parser": "^7.26",
+    "@babel/plugin-syntax-typescript": "^7.25.9",
+    "@modelcontextprotocol/sdk": "^1.9.0",
+    "algoliasearch": "^5.23.3",
+    "cheerio": "^1.0.0",
+    "prettier": "^3.3.3",
+    "turndown": "^7.2.0",
+    "zod": "^3.23.8"
+  },
+  "devDependencies": {
+    "@types/turndown": "^5.0.5"
+  },
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/facebook/react.git",
+    "directory": "compiler/packages/react-mcp-server"
+  }
+}

compiler/packages/react-mcp-server/src/compiler/index.ts

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+/**
+ * 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.
+ */
+
+import type * as BabelCore from '@babel/core';
+import {parseAsync, transformFromAstAsync} from '@babel/core';
+import BabelPluginReactCompiler, {
+  type PluginOptions,
+} from 'babel-plugin-react-compiler/src';
+import * as prettier from 'prettier';
+
+export let lastResult: BabelCore.BabelFileResult | null = null;
+
+type CompileOptions = {
+  text: string;
+  file: string;
+  options: Partial<PluginOptions> | null;
+};
+export async function compile({
+  text,
+  file,
+  options,
+}: CompileOptions): Promise<BabelCore.BabelFileResult> {
+  const ast = await parseAsync(text, {
+    sourceFileName: file,
+    parserOpts: {
+      plugins: ['typescript', 'jsx'],
+    },
+    sourceType: 'module',
+  });
+  if (ast == null) {
+    throw new Error('Could not parse');
+  }
+  const plugins =
+    options != null
+      ? [[BabelPluginReactCompiler, options]]
+      : [[BabelPluginReactCompiler]];
+  const result = await transformFromAstAsync(ast, text, {
+    filename: file,
+    highlightCode: false,
+    retainLines: true,
+    plugins,
+    sourceType: 'module',
+    sourceFileName: file,
+  });
+  if (result?.code == null) {
+    throw new Error(
+      `Expected BabelPluginReactCompiler to compile successfully, got ${result}`,
+    );
+  }
+  try {
+    result.code = await prettier.format(result.code, {
+      semi: false,
+      parser: 'babel-ts',
+    });
+    if (result.code != null) {
+      lastResult = result;
+    }
+  } catch (err) {
+    // If prettier failed just log, no need to crash
+    console.error(err);
+  }
+  return result;
+}