From e28c8ac612e2a39147b92cfd97307469a007ab44 Mon Sep 17 00:00:00 2001
From: Brian Ng <bng412@gmail.com>
Date: Fri, 11 Oct 2019 20:22:42 -0500
Subject: [PATCH] Fix generator missing parens around an arrow returning
 function type (#10519)

---
 packages/babel-generator/src/node/parentheses.js     | 12 ++++++++++--
 .../test/fixtures/flow/arrow-functions/input.js      |  1 +
 .../test/fixtures/flow/arrow-functions/output.js     |  4 +++-
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/packages/babel-generator/src/node/parentheses.js b/packages/babel-generator/src/node/parentheses.js
index 8c38fa627239..0a1ab115c529 100644
--- a/packages/babel-generator/src/node/parentheses.js
+++ b/packages/babel-generator/src/node/parentheses.js
@@ -35,14 +35,22 @@ export function NullableTypeAnnotation(node: Object, parent: Object): boolean {
   return t.isArrayTypeAnnotation(parent);
 }
 
-export function FunctionTypeAnnotation(node: Object, parent: Object): boolean {
+export function FunctionTypeAnnotation(
+  node: Object,
+  parent: Object,
+  printStack: Array<Object>,
+): boolean {
   return (
     // (() => A) | (() => B)
     t.isUnionTypeAnnotation(parent) ||
     // (() => A) & (() => B)
     t.isIntersectionTypeAnnotation(parent) ||
     // (() => A)[]
-    t.isArrayTypeAnnotation(parent)
+    t.isArrayTypeAnnotation(parent) ||
+    // <T>(A: T): (T => T[]) => B => [A, B]
+    (t.isTypeAnnotation(parent) &&
+      // Check grandparent
+      t.isArrowFunctionExpression(printStack[printStack.length - 3]))
   );
 }
 
diff --git a/packages/babel-generator/test/fixtures/flow/arrow-functions/input.js b/packages/babel-generator/test/fixtures/flow/arrow-functions/input.js
index a3d11b136d6b..5719c2dbf087 100644
--- a/packages/babel-generator/test/fixtures/flow/arrow-functions/input.js
+++ b/packages/babel-generator/test/fixtures/flow/arrow-functions/input.js
@@ -5,3 +5,4 @@ const bar4 = x => {};
 const bar5 = (x): string => {};
 const bar6 = (x: number) => {};
 const bar7 = <T>(x) => {};
+const bar8 = <T>(x: T): (T => T[]) => y => [x, y];
diff --git a/packages/babel-generator/test/fixtures/flow/arrow-functions/output.js b/packages/babel-generator/test/fixtures/flow/arrow-functions/output.js
index 8b1f78020541..d132971e4bcf 100644
--- a/packages/babel-generator/test/fixtures/flow/arrow-functions/output.js
+++ b/packages/babel-generator/test/fixtures/flow/arrow-functions/output.js
@@ -10,4 +10,6 @@ const bar5 = (x): string => {};
 
 const bar6 = (x: number) => {};
 
-const bar7 = <T>(x) => {};
\ No newline at end of file
+const bar7 = <T>(x) => {};
+
+const bar8 = <T>(x: T): ((T) => T[]) => y => [x, y];