Mark 'React' symbol as used and error if it doesn't exist

Author: RyanCavanaugh

src/compiler/checker.ts

@@ -7299,6 +7299,16 @@ namespace ts {
             checkGrammarJsxElement(node);
             checkJsxPreconditions(node);
 
+            // If we're compiling under --jsx react, the symbol 'React' should
+            // be marked as 'used' so we don't incorrectly elide its import. And if there
+            // is no 'React' symbol in scope, we should issue an error.
+            if(compilerOptions.jsx === JsxEmit.React) {
+                let reactSym = resolveName(node.tagName, 'React', SymbolFlags.Value, Diagnostics.Cannot_find_name_0, 'React');
+                if (reactSym) {
+                    getSymbolLinks(reactSym).referenced = true;
+                }
+            }
+
             let targetAttributesType = getJsxElementAttributesType(node);
 
             if (getNodeLinks(node).jsxFlags & JsxFlags.ClassElement) {

tests/baselines/reference/tsxElementResolution19.js

@@ -31,6 +31,6 @@ define(["require", "exports"], function (require, exports) {
     exports.MyClass = MyClass;
 });
 //// [file2.js]
-define(["require", "exports", './file1'], function (require, exports, file1_1) {
+define(["require", "exports", 'react', './file1'], function (require, exports, React, file1_1) {
     React.createElement(file1_1.MyClass, null);
 });