[react jsx transform] Spread attribute -> Object.assign

Add support for spread attributes. Transforms into an Object.assign just
like jstransform does for spread properties in object literals.

Depends on https://github.com/facebook/esprima/pull/22

vendor/fbtransform/transforms/__tests__/react-test.js

@@ -30,6 +30,26 @@ describe('react jsx', function() {
     );
   };
 
+  // These are placeholder variables in scope that we can use to assert that a
+  // specific variable reference was passed, rather than an object clone of it.
+  var x = 123456;
+  var y = 789012;
+  var z = 345678;
+
+  var HEADER =
+    '/**\n' +
+    ' * @jsx React.DOM\n' +
+    ' */\n';
+
+  var expectObjectAssign = function(code) {
+    var Component = jest.genMockFunction();
+    var Child = jest.genMockFunction();
+    var objectAssignMock = jest.genMockFunction();
+    Object.assign = objectAssignMock;
+    eval(transform(HEADER + code).code);
+    return expect(objectAssignMock);
+  }
+
   it('should convert simple tags', function() {
     var code = [
       '/**@jsx React.DOM*/',
@@ -357,4 +377,54 @@ describe('react jsx', function() {
     expect(() => transform(code)).toThrow();
   });
 
+  it('wraps props in Object.assign for spread attributes', function() {
+    var code = HEADER +
+      '<Component { ... x } y\n={2 } z />';
+    var result = HEADER +
+      'Component(Object.assign({},   x , {y: \n2, z: true}))';
+    expect(transform(code).code).toBe(result);
+  });
+
+  it('does not call Object.assign when there are no spreads', function() {
+    expectObjectAssign(
+      '<Component x={y} />'
+    ).not.toBeCalled();
+  });
+
+  it('calls assign with a new target object for spreads', function() {
+    expectObjectAssign(
+      '<Component {...x} />'
+    ).toBeCalledWith({}, x);
+  });
+
+  it('calls assign with an empty object when the spread is first', function() {
+    expectObjectAssign(
+      '<Component { ...x } y={2} />'
+    ).toBeCalledWith({}, x, { y: 2 });
+  });
+
+  it('coalesces consecutive properties into a single object', function() {
+    expectObjectAssign(
+      '<Component { ... x } y={2} z />'
+    ).toBeCalledWith({}, x, { y: 2, z: true });
+  });
+
+  it('avoids an unnecessary empty object when spread is not first', function() {
+    expectObjectAssign(
+      '<Component x={1} {...y} />'
+    ).toBeCalledWith({x: 1}, y);
+  });
+
+  it('passes the same value multiple times to Object.assign', function() {
+    expectObjectAssign(
+      '<Component x={1} y="2" {...z} {...z}><Child /></Component>'
+    ).toBeCalledWith({x: 1, y: "2"}, z, z);
+  });
+
+  it('evaluates sequences before passing them to Object.assign', function() {
+    expectObjectAssign(
+      '<Component x="1" {...(z = { y: 2 }, z)} z={3}>Text</Component>'
+    ).toBeCalledWith({x: "1"}, { y: 2 }, {z: 3});
+  });
+
 });

vendor/fbtransform/transforms/react.js

@@ -49,6 +49,14 @@ var JSX_ATTRIBUTE_TRANSFORMS = {
   }
 };
 
+/**
+ * Removes all non-whitespace/parenthesis characters
+ */
+var reNonWhiteParen = /([^\s\(\)])/g;
+function stripNonWhiteParen(value) {
+  return value.replace(reNonWhiteParen, '');
+}
+
 function visitReactTag(traverse, object, path, state) {
   var jsxObjIdent = utils.getDocblock(state).jsx;
   var openingElement = object.openingElement;
@@ -57,6 +65,7 @@ function visitReactTag(traverse, object, path, state) {
 
   utils.catchup(openingElement.range[0], state, trimLeft);
 
+
   if (nameObject.type === Syntax.XJSNamespacedName && nameObject.namespace) {
     throw new Error('Namespace tags are not supported. ReactJSX is not XML.');
   }
@@ -75,23 +84,74 @@ function visitReactTag(traverse, object, path, state) {
 
   var hasAttributes = attributesObject.length;
 
+  var hasAtLeastOneSpreadProperty = attributesObject.some(function(attr) {
+    return attr.type === Syntax.XJSSpreadAttribute;
+  });
+
   // if we don't have any attributes, pass in null
-  if (hasAttributes) {
+  if (hasAtLeastOneSpreadProperty) {
+    utils.append('Object.assign({', state);
+  } else if (hasAttributes) {
     utils.append('{', state);
   } else {
     utils.append('null', state);
   }
 
+  // keep track of if the previous attribute was a spread attribute
+  var previousWasSpread = false;
+
   // write attributes
   attributesObject.forEach(function(attr, index) {
+    var isLast = index === attributesObject.length - 1;
+
+    if (attr.type === Syntax.XJSSpreadAttribute) {
+      // Plus 1 to skip `{`.
+      utils.move(attr.range[0] + 1, state);
+
+      // Close the previous object or initial object
+      if (!previousWasSpread) {
+        utils.append('}, ', state);
+      }
+
+      // Move to the expression start, ignoring everything except parenthesis
+      // and whitespace.
+      utils.catchup(attr.argument.range[0], state, stripNonWhiteParen);
+
+      traverse(attr.argument, path, state);
+
+      utils.catchup(attr.argument.range[1], state);
+
+      // Move to the end, ignoring parenthesis and the closing `}`
+      utils.catchup(attr.range[1] - 1, state, stripNonWhiteParen);
+
+      if (!isLast) {
+        utils.append(', ', state);
+      }
+
+      utils.move(attr.range[1], state);
+
+      previousWasSpread = true;
+
+      return;
+    }
+
+    // If the next attribute is a spread, we're effective last in this object
+    if (!isLast) {
+      isLast = attributesObject[index + 1].type === Syntax.XJSSpreadAttribute;
+    }
+
     if (attr.name.namespace) {
       throw new Error(
          'Namespace attributes are not supported. ReactJSX is not XML.');
     }
     var name = attr.name.name;
-    var isLast = index === attributesObject.length - 1;
 
     utils.catchup(attr.range[0], state, trimLeft);
+
+    if (previousWasSpread) {
+      utils.append('{', state);
+    }
+
     utils.append(quoteAttrName(name), state);
     utils.append(': ', state);
 
@@ -119,6 +179,9 @@ function visitReactTag(traverse, object, path, state) {
     }
 
     utils.catchup(attr.range[1], state, trimLeft);
+
+    previousWasSpread = false;
+
   });
 
   if (!openingElement.selfClosing) {
@@ -126,10 +189,14 @@ function visitReactTag(traverse, object, path, state) {
     utils.move(openingElement.range[1], state);
   }
 
-  if (hasAttributes) {
+  if (hasAttributes && !previousWasSpread) {
     utils.append('}', state);
   }
 
+  if (hasAtLeastOneSpreadProperty) {
+    utils.append(')', state);
+  }
+
   // filter out whitespace
   var childrenToRender = object.children.filter(function(child) {
     return !(child.type === Syntax.Literal