Don't add () in JSX attributes with elements (#3640)

src/language-js/printer-estree.js

@@ -4477,6 +4477,7 @@ function maybeWrapJSXElementInParens(path, elem) {
 
   const NO_WRAP_PARENTS = {
     ArrayExpression: true,
+    JSXAttribute: true,
     JSXElement: true,
     JSXExpressionContainer: true,
     JSXFragment: true,

tests/jsx-attr-element/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,20 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`attr-element.js 1`] = `
+<Foo prop=<Bar><Baz /></Bar> />;
+<Foo prop=<><Bar><Baz /></Bar></> />;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+<Foo
+  prop=<Bar>
+    <Baz />
+  </Bar>
+/>;
+<Foo
+  prop=<>
+    <Bar>
+      <Baz />
+    </Bar>
+  </>
+/>;
+
+`;

tests/jsx-attr-element/attr-element.js

@@ -0,0 +1,2 @@
+<Foo prop=<Bar><Baz /></Bar> />;
+<Foo prop=<><Bar><Baz /></Bar></> />;

tests/jsx-attr-element/jsfmt.spec.js

@@ -0,0 +1,2 @@
+// Flow and TypeScript don't support JSX elements as attribute values
+run_spec(__dirname, ["babylon"]);