Add parenthesis around single argument arrow if comments (#573)

Fixes #568

src/printer.js

@@ -261,6 +261,8 @@ function genericPrintNoParens(path, options, print) {
           !n.rest &&
           n.params[0].type === "Identifier" &&
           !n.params[0].typeAnnotation &&
+          !n.params[0].leadingComments &&
+          !n.params[0].trailingComments &&
           !n.predicate &&
           !n.returnType
       ) {

tests/flow_comments/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,29 @@
+exports[`test arrow.js 1`] = `
+"// Error
+const beep = (data/*: Object*/) => {}
+
+// OK
+const beep = (data/*: Object*/, secondData/*: Object*/) => {}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// Error
+const beep = (data: Object) => {};
+
+// OK
+const beep = (data: Object, secondData: Object) => {};
+"
+`;
+
+exports[`test arrow.js 2`] = `
+"// Error
+const beep = (data/*: Object*/) => {}
+
+// OK
+const beep = (data/*: Object*/, secondData/*: Object*/) => {}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// Error
+const beep = (data /*: Object*/) => {};
+
+// OK
+const beep = (data /*: Object*/, secondData /*: Object*/) => {};
+"
+`;

tests/flow_comments/arrow.js

@@ -0,0 +1,5 @@
+// Error
+const beep = (data/*: Object*/) => {}
+
+// OK
+const beep = (data/*: Object*/, secondData/*: Object*/) => {}

tests/flow_comments/jsfmt.spec.js

@@ -0,0 +1,2 @@
+run_spec(__dirname);
+run_spec(__dirname, {parser: 'babylon'});