Make React.__spread warn

scripts/babel/transform-object-assign-require.js

@@ -12,6 +12,20 @@
 module.exports = function autoImporter(babel) {
   const t = babel.types;
 
+  function getAssignIdent(path, file, state) {
+    if (!state.id) {
+      state.id = path.scope.generateUidIdentifier('assign');
+      path.scope.getProgramParent().push({
+        id: state.id,
+        init: t.callExpression(
+          t.identifier('require'),
+          [t.stringLiteral('object-assign')]
+        ),
+      });
+    }
+    return state.id;
+  }
+
   return {
     pre: function() {
       // map from module to generated identifier
@@ -22,17 +36,15 @@ module.exports = function autoImporter(babel) {
       CallExpression: function(path, file) {
         if (path.get('callee').matchesPattern('Object.assign')) {
           // generate identifier and require if it hasn't been already
-          if (!this.id) {
-            this.id = path.scope.generateUidIdentifier('assign');
-            path.scope.getProgramParent().push({
-              id: this.id,
-              init: t.callExpression(
-                t.identifier('require'),
-                [t.stringLiteral('object-assign')]
-              ),
-            });
-          }
-          path.node.callee = this.id;
+          var id = getAssignIdent(path, file, this);
+          path.node.callee = id;
+        }
+      },
+
+      MemberExpression: function(path, file) {
+        if (path.matchesPattern('Object.assign')) {
+          var id = getAssignIdent(path, file, this);
+          path.replaceWith(id);
         }
       },
     },

src/isomorphic/React.js

@@ -21,6 +21,7 @@ var ReactPropTypes = require('ReactPropTypes');
 var ReactVersion = require('ReactVersion');
 
 var onlyChild = require('onlyChild');
+var warning = require('warning');
 
 var createElement = ReactElement.createElement;
 var createFactory = ReactElement.createFactory;
@@ -32,6 +33,23 @@ if (__DEV__) {
   cloneElement = ReactElementValidator.cloneElement;
 }
 
+var __spread = Object.assign;
+
+if (__DEV__) {
+  var warned = false;
+  __spread = function() {
+    warning(
+      warned,
+      'React.__spread is deprecated and should not be used. Use ' +
+      'Object.assign directly or another helper function with similar ' +
+      'semantics. You may be seeing this warning due to your compiler. ' +
+      'See https://fb.me/react-spread-deprecation for more details.'
+    );
+    warned = true;
+    return Object.assign.apply(null, arguments);
+  };
+}
+
 var React = {
 
   // Modern
@@ -66,8 +84,8 @@ var React = {
 
   version: ReactVersion,
 
-  // Hook for JSX spread, don't use this for anything else.
-  __spread: Object.assign,
+  // Deprecated hook for JSX spread, don't use this for anything.
+  __spread: __spread,
 };
 
 module.exports = React;