From 58c6b42aa80ea8681c3b8aaaf8f891c9e4f15e51 Mon Sep 17 00:00:00 2001
From: Georgii Dolzhykov <thorn.mailbox@gmail.com>
Date: Sat, 9 Nov 2019 12:47:54 +0200
Subject: [PATCH] fix formatting of union type as arrow function return type
 (#6896)

---
 changelog_unreleased/typescript/pr-6896.md    | 22 +++++++++++++
 src/language-js/printer-estree.js             |  3 ++
 .../__snapshots__/jsfmt.spec.js.snap          | 33 +++++++++++++++++++
 tests/typescript_generic/arrow-return-type.ts | 12 +++++++
 4 files changed, 70 insertions(+)
 create mode 100644 changelog_unreleased/typescript/pr-6896.md
 create mode 100644 tests/typescript_generic/arrow-return-type.ts

diff --git a/changelog_unreleased/typescript/pr-6896.md b/changelog_unreleased/typescript/pr-6896.md
new file mode 100644
index 000000000000..e5cfea359fa5
--- /dev/null
+++ b/changelog_unreleased/typescript/pr-6896.md
@@ -0,0 +1,22 @@
+#### Fix formatting of union type as arrow function return type ([#6896](https://github.com/prettier/prettier/pull/6896) by [@thorn0](https://github.com/thorn0))
+
+<!-- prettier-ignore -->
+```jsx
+// Input
+export const getVehicleDescriptor = async (
+  vehicleId: string,
+): Promise<Collections.Parts.PrintedCircuitBoardAssembly['attributes'] | undefined> => {}
+
+// Prettier stable
+export const getVehicleDescriptor = async (
+  vehicleId: string
+): Promise<| Collections.Parts.PrintedCircuitBoardAssembly["attributes"]
+| undefined> => {};
+
+// Prettier master
+export const getVehicleDescriptor = async (
+  vehicleId: string
+): Promise<
+  Collections.Parts.PrintedCircuitBoardAssembly["attributes"] | undefined
+> => {};
+```
diff --git a/src/language-js/printer-estree.js b/src/language-js/printer-estree.js
index 82967e586c71..14a3fa9dacd1 100644
--- a/src/language-js/printer-estree.js
+++ b/src/language-js/printer-estree.js
@@ -4587,10 +4587,13 @@ function printTypeParameters(path, options, print, paramsKey) {
         (n[paramsKey][0].type === "TSTypeReference" &&
           shouldHugType(n[paramsKey][0].typeName)) ||
         n[paramsKey][0].type === "NullableTypeAnnotation" ||
+        // See https://github.com/prettier/prettier/pull/6467 for the context.
         (greatGreatGrandParent &&
           greatGreatGrandParent.type === "VariableDeclarator" &&
           grandparent &&
           grandparent.type === "TSTypeAnnotation" &&
+          n[paramsKey][0].type !== "TSUnionType" &&
+          n[paramsKey][0].type !== "UnionTypeAnnotation" &&
           n[paramsKey][0].type !== "TSConditionalType" &&
           n[paramsKey][0].type !== "TSMappedType")));
 
diff --git a/tests/typescript_generic/__snapshots__/jsfmt.spec.js.snap b/tests/typescript_generic/__snapshots__/jsfmt.spec.js.snap
index 3009a3eb7513..30c3a0efaba7 100644
--- a/tests/typescript_generic/__snapshots__/jsfmt.spec.js.snap
+++ b/tests/typescript_generic/__snapshots__/jsfmt.spec.js.snap
@@ -1,5 +1,38 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`arrow-return-type.ts 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+export const getVehicleDescriptor = async (
+  vehicleId: string,
+): Promise<
+  Descriptor | undefined
+> => {}
+
+
+export const getVehicleDescriptor = async (
+  vehicleId: string,
+): Promise<
+  Collections.Parts.PrintedCircuitBoardAssembly['attributes'] | undefined
+> => {}
+
+=====================================output=====================================
+export const getVehicleDescriptor = async (
+  vehicleId: string
+): Promise<Descriptor | undefined> => {};
+
+export const getVehicleDescriptor = async (
+  vehicleId: string
+): Promise<
+  Collections.Parts.PrintedCircuitBoardAssembly["attributes"] | undefined
+> => {};
+
+================================================================================
+`;
+
 exports[`object-method.ts 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]
diff --git a/tests/typescript_generic/arrow-return-type.ts b/tests/typescript_generic/arrow-return-type.ts
new file mode 100644
index 000000000000..0d05ca494782
--- /dev/null
+++ b/tests/typescript_generic/arrow-return-type.ts
@@ -0,0 +1,12 @@
+export const getVehicleDescriptor = async (
+  vehicleId: string,
+): Promise<
+  Descriptor | undefined
+> => {}
+
+
+export const getVehicleDescriptor = async (
+  vehicleId: string,
+): Promise<
+  Collections.Parts.PrintedCircuitBoardAssembly['attributes'] | undefined
+> => {}