Don't print an extra line break for arrow function with type parameter in assignment (#16586)

* Dont print extra softline

* Update snapshot

* Add changelog

changelog_unreleased/typescript/16586.md

@@ -0,0 +1,28 @@
+#### Don't print an extra line break for arrow function with type parameter in assignment (#16586 by @sosukesuzuki)
+
+There was a bug where an extra line was inserted when assigning a chained arrow function with type parameters to a variable if there was a line comment above it.
+
+This change ensures that the extra line is no longer inserted.
+
+<!-- prettier-ignore -->
+```tsx
+// Input
+const foo1 = 
+  // comment
+  <T,>() => () => 1;
+
+// Prettier stable
+const foo1 =
+  // comment
+
+    <T,>() =>
+    () =>
+      1;
+
+// Prettier main
+const foo1 =
+  // comment
+  <T,>() =>
+    () =>
+      1;
+```

src/language-js/print/arrow-function.js

@@ -16,6 +16,7 @@ import {
 import getNextNonSpaceNonCommentCharacterIndex from "../../utils/get-next-non-space-non-comment-character-index.js";
 import { locEnd } from "../loc.js";
 import {
+  CommentCheckFlags,
   getFunctionParameters,
   hasComment,
   hasLeadingOwnLineComment,
@@ -119,8 +120,9 @@ function printArrowFunction(path, options, print, args = {}) {
     signatureDocs,
     shouldBreak: shouldBreakChain,
   });
-  let shouldBreakSignatures;
+  let shouldBreakSignatures = false;
   let shouldIndentSignatures = false;
+  let shouldPrintSoftlineInIndent = false;
   if (
     shouldPrintAsChain &&
     (isCallee ||
@@ -128,6 +130,13 @@ function printArrowFunction(path, options, print, args = {}) {
       args.assignmentLayout)
   ) {
     shouldIndentSignatures = true;
+    // If the arrow function has a leading line comment, there should be a hardline above it
+    // so we should not print a softline in indent call
+    // https://github.com/prettier/prettier/issues/16067
+    shouldPrintSoftlineInIndent = !hasComment(
+      path.node,
+      CommentCheckFlags.Leading & CommentCheckFlags.Line,
+    );
     shouldBreakSignatures =
       args.assignmentLayout === "chain-tail-arrow-chain" ||
       (isCallee && !shouldPutBodyOnSameLine);
@@ -143,7 +152,7 @@ function printArrowFunction(path, options, print, args = {}) {
   return group([
     group(
       shouldIndentSignatures
-        ? indent([softline, signaturesDoc])
+        ? indent([shouldPrintSoftlineInIndent ? softline : "", signaturesDoc])
         : signaturesDoc,
       { shouldBreak: shouldBreakSignatures, id: chainGroupId },
     ),

tests/format/typescript/arrow/16067.ts

@@ -0,0 +1,35 @@
+const foo1 = 
+  // comment
+  <T>() => () => 1;
+
+const foo2 = 
+  // comment
+  () => () => 1;
+
+const foo3 = 
+  // comment
+  <T>() => 1;
+
+foo(
+  // comment
+  <T>() => () => 1,
+);
+
+a ||
+  // comment
+  (<T>() => () => 1);
+
+void
+  // comment
+  (<T>() => () => 1);
+
+cond ?
+  // comment
+  <T>() => () => 1
+  :
+  // comment
+  <T>() => () => 1;
+
+foo4 = 
+  // comment
+  <T>() => () => 1;

tests/format/typescript/arrow/__snapshots__/format.test.js.snap

@@ -1,5 +1,198 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`16067.ts - {"semi":false} format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+semi: false
+                                                                                | printWidth
+=====================================input======================================
+const foo1 = 
+  // comment
+  <T>() => () => 1;
+
+const foo2 = 
+  // comment
+  () => () => 1;
+
+const foo3 = 
+  // comment
+  <T>() => 1;
+
+foo(
+  // comment
+  <T>() => () => 1,
+);
+
+a ||
+  // comment
+  (<T>() => () => 1);
+
+void
+  // comment
+  (<T>() => () => 1);
+
+cond ?
+  // comment
+  <T>() => () => 1
+  :
+  // comment
+  <T>() => () => 1;
+
+foo4 = 
+  // comment
+  <T>() => () => 1;
+
+=====================================output=====================================
+const foo1 =
+  // comment
+  <T>() =>
+    () =>
+      1
+
+const foo2 =
+  // comment
+  () => () => 1
+
+const foo3 =
+  // comment
+  <T>() => 1
+
+foo(
+  // comment
+  <T>() =>
+    () =>
+      1,
+)
+
+a ||
+  // comment
+  (<T>() =>
+    () =>
+      1)
+
+void (
+  // comment
+  (<T>() =>
+    () =>
+      1)
+)
+
+cond
+  ? // comment
+    <T>() =>
+      () =>
+        1
+  : // comment
+    <T>() =>
+      () =>
+        1
+
+foo4 =
+  // comment
+  <T>() =>
+    () =>
+      1
+
+================================================================================
+`;
+
+exports[`16067.ts format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+const foo1 = 
+  // comment
+  <T>() => () => 1;
+
+const foo2 = 
+  // comment
+  () => () => 1;
+
+const foo3 = 
+  // comment
+  <T>() => 1;
+
+foo(
+  // comment
+  <T>() => () => 1,
+);
+
+a ||
+  // comment
+  (<T>() => () => 1);
+
+void
+  // comment
+  (<T>() => () => 1);
+
+cond ?
+  // comment
+  <T>() => () => 1
+  :
+  // comment
+  <T>() => () => 1;
+
+foo4 = 
+  // comment
+  <T>() => () => 1;
+
+=====================================output=====================================
+const foo1 =
+  // comment
+  <T>() =>
+    () =>
+      1;
+
+const foo2 =
+  // comment
+  () => () => 1;
+
+const foo3 =
+  // comment
+  <T>() => 1;
+
+foo(
+  // comment
+  <T>() =>
+    () =>
+      1,
+);
+
+a ||
+  // comment
+  (<T>() =>
+    () =>
+      1);
+
+void (
+  // comment
+  (<T>() =>
+    () =>
+      1)
+);
+
+cond
+  ? // comment
+    <T>() =>
+      () =>
+        1
+  : // comment
+    <T>() =>
+      () =>
+        1;
+
+foo4 =
+  // comment
+  <T>() =>
+    () =>
+      1;
+
+================================================================================
+`;
+
 exports[`arrow_regression.ts - {"semi":false} format 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]