Flow: Fix generating arrow functions with param

packages/babel-generator/src/generators/methods.js

@@ -77,8 +77,14 @@ export function ArrowFunctionExpression(node: Object) {
     this.space();
   }
 
-  if (node.params.length === 1 && t.isIdentifier(node.params[0])) {
-    this.print(node.params[0], node);
+  let param;
+
+  if (
+    node.params.length === 1
+    && t.isIdentifier(param = node.params[0])
+    && !(node.typeParameters || node.returnType || param.typeAnnotation || param.optional || param.trailingComments)
+  ) {
+    this.print(param, node);
   } else {
     this._params(node);
   }

packages/babel-generator/test/fixtures/flow/arrow-functions/actual.js

@@ -0,0 +1,7 @@
+const bar1 = (x: number): string => {};
+const bar2 = (x?) => {};
+const bar3 = (x?: string) => {};
+const bar4 = x => {};
+const bar5 = (x): string => {};
+const bar6 = (x: number) => {};
+const bar7 = <T>(x) => {};

packages/babel-generator/test/fixtures/flow/arrow-functions/expected.js

@@ -0,0 +1,7 @@
+const bar1 = (x: number): string => {};
+const bar2 = (x?) => {};
+const bar3 = (x?: string) => {};
+const bar4 = x => {};
+const bar5 = (x): string => {};
+const bar6 = (x: number) => {};
+const bar7 = <T>(x) => {};

packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/arrow-single-optional-param/actual.js

@@ -0,0 +1 @@
+const x = (foo?) => {}

packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/arrow-single-optional-param/expected.js

@@ -0,0 +1 @@
+const x = (foo /*:: ?*/) => {};

packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/arrow-single-param-type/actual.js

@@ -0,0 +1 @@
+const x = (foo: string) => {};

packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/arrow-single-param-type/expected.js

@@ -0,0 +1 @@
+const x = (foo /*: string*/) => {};