Fix parens in inferred function return types with extends (#13289)

GlebDolzhikov · web-flow · commit f2244bdc8621 · 2022-08-17T18:36:25.000+03:00
Co-authored-by: Gleb Dolzhikov &lt;9276677@gmail.com&gt;
diff --git a/changelog_unreleased/typescript/13289.md b/changelog_unreleased/typescript/13289.md
@@ -0,0 +1,13 @@
+#### Fix parens in inferred function return types with `extends` (#13289 by @GlebDolzhikov)
+
+<!-- prettier-ignore -->
+```ts
+// Input
+type Foo<T> = T extends (...a: any[]) => (infer R extends string) ? R : never;
+
+// Prettier stable
+type Foo<T> = T extends (...a: any[]) => infer R extends string ? R : never;
+
+// Prettier main
+type Foo<T> = T extends ((...a: any[]) => infer R extends string) ? R : never;
+```
diff --git a/src/language-js/needs-parens.js b/src/language-js/needs-parens.js
@@ -412,6 +412,16 @@ function needsParens(path, options) {
     // fallthrough
     case "TSFunctionType":
     case "TSConstructorType":
+      if (name === "extendsType" && parent.type === "TSConditionalType") {
+        const returnTypeAnnotation = (node.returnType || node.typeAnnotation)
+          .typeAnnotation;
+        if (
+          returnTypeAnnotation.type === "TSInferType" &&
+          returnTypeAnnotation.typeParameter.constraint
+        ) {
+          return true;
+        }
+      }
       if (name === "checkType" && parent.type === "TSConditionalType") {
         return true;
       }
diff --git a/tests/format/typescript/conditional-types/__snapshots__/jsfmt.spec.js.snap b/tests/format/typescript/conditional-types/__snapshots__/jsfmt.spec.js.snap
@@ -278,6 +278,20 @@ type Unpacked<T> = T extends (infer U)[]
 ================================================================================
 `;
 
+exports[`issue-13275.ts format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+type Foo<T> = T extends ((...a: any[]) => infer R extends string) ? R : never;
+
+=====================================output=====================================
+type Foo<T> = T extends ((...a: any[]) => infer R extends string) ? R : never;
+
+================================================================================
+`;
+
 exports[`nested-in-condition.ts format 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]
diff --git a/tests/format/typescript/conditional-types/issue-13275.ts b/tests/format/typescript/conditional-types/issue-13275.ts
@@ -0,0 +1 @@
+type Foo<T> = T extends ((...a: any[]) => infer R extends string) ? R : never;

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+type Foo<T> = T extends ((...a: any[]) => infer R extends string) ? R : never;`