Use "react-server" convention to enforce that writer is only loaded i…

…n a server

packages/react-server-dom-webpack/npm/writer.js

@@ -1,3 +1,6 @@
 'use strict';
 
-module.exports = require('./writer.node.server');
+throw new Error(
+  'The React Server Writer cannot be used outside a react-server environment. ' +
+    'You must configure Node.js using the `--conditions react-server` flag.'
+);

packages/react-server-dom-webpack/package.json

@@ -25,9 +25,15 @@
   "exports": {
     ".": "./index.js",
     "./plugin": "./plugin.js",
-    "./writer": "./writer.js",
-    "./writer.browser.server": "./writer.browser.server.js",
+    "./writer": {
+      "react-server": {
+        "node": "./writer.node.server.js",
+        "browser": "./writer.browser.server.js"
+      },
+      "default": "./writer.js"
+    },
     "./writer.node.server": "./writer.node.server.js",
+    "./writer.browser.server": "./writer.browser.server.js",
     "./node-loader": "./esm/react-server-dom-webpack-node-loader.js",
     "./node-register": "./node-register.js",
     "./package.json": "./package.json"

packages/react-server-dom-webpack/src/__tests__/ReactFlightDOM-test.js

@@ -40,7 +40,7 @@ describe('ReactFlightDOM', () => {
     Stream = require('stream');
     React = require('react');
     ReactDOM = require('react-dom');
-    ReactServerDOMWriter = require('react-server-dom-webpack/writer');
+    ReactServerDOMWriter = require('react-server-dom-webpack/writer.node.server');
     ReactServerDOMReader = require('react-server-dom-webpack');
   });
 

packages/react-server-dom-webpack/writer.js

@@ -7,4 +7,7 @@
  * @flow
  */
 
-export * from './writer.node.server';
+throw new Error(
+  'The React Server Writer cannot be used outside a react-server environment. ' +
+    'You must configure Node.js using the `--conditions react-server` flag.',
+);