Fix assert false type parameter variables

packages/babel-plugin-flow-runtime/src/__tests__/__fixtures__/bugs/180-assert-false-type-parameter.js

@@ -0,0 +1,30 @@
+/* @flow */
+
+export const input = `
+function foo<X>() {
+  let bar: X;
+}
+`;
+
+export const expected = `
+import t from "flow-runtime";
+
+function foo() {
+  const X = t.typeParameter("X");
+  let _barType = X,
+      bar;
+}
+`;
+
+export const annotated = `
+import t from "flow-runtime";
+
+function foo() {
+  let bar;
+}
+
+t.annotate(foo, t.function(_fn => {
+  const X = _fn.typeParameter("X");
+  return [];
+}));
+`;

packages/babel-plugin-flow-runtime/src/transformVisitors.js

@@ -216,16 +216,17 @@ export default function transformVisitors (context: ConversionContext): Object {
       if (!id.has('typeAnnotation')) {
         return;
       }
+      if (!shouldCheck) {
+        return;
+      }
       if (!id.isIdentifier()) {
         invariant(id.isArrayPattern() || id.isObjectPattern());
         const init = path.get('init');
         let wrapped = init.node;
-        if (shouldCheck) {
-          wrapped = context.assert(
-            convert(context, id.get('typeAnnotation')),
-            wrapped
-          );
-        }
+        wrapped = context.assert(
+          convert(context, id.get('typeAnnotation')),
+          wrapped
+        );
         if (wrapped !== init.node) {
           context.replacePath(init, wrapped);
         }