Allow plugins to assert that a specific babel version has loaded the plugin. (#7450)

packages/babel-plugin-transform-react-jsx/src/index.js

@@ -1,8 +1,11 @@
+import { declare } from "@babel/helper-plugin-utils";
 import jsx from "@babel/plugin-syntax-jsx";
 import helper from "@babel/helper-builder-react-jsx";
 import { types as t } from "@babel/core";
 
-export default function(api, options) {
+export default declare((api, options) => {
+  api.assertVersion(7);
+
   const THROW_IF_NAMESPACE =
     options.throwIfNamespace === undefined ? true : !!options.throwIfNamespace;
 
@@ -91,4 +94,4 @@ export default function(api, options) {
     inherits: jsx,
     visitor,
   };
-}
+});