From aa10aa4b1e42ead7759d0870be8d3be71b0570ae Mon Sep 17 00:00:00 2001
From: fisker Cheung <lionkay@gmail.com>
Date: Thu, 25 Jun 2026 10:34:02 +0800
Subject: [PATCH] Fix comments on right side of "assignment like" (#19456)

---
 src/language-js/comments/handle-comments.js   | 22 +++++++------
 .../__snapshots__/format.test.js.snap         | 32 ++++++-------------
 .../__snapshots__/format.test.js.snap         |  4 +--
 3 files changed, 24 insertions(+), 34 deletions(-)

diff --git a/src/language-js/comments/handle-comments.js b/src/language-js/comments/handle-comments.js
index e737f57b3..797e43af0 100644
--- a/src/language-js/comments/handle-comments.js
+++ b/src/language-js/comments/handle-comments.js
@@ -26,6 +26,7 @@ import {
   isConditionalType,
   isIntersectionType,
   isMemberExpression,
+  isTypeAlias,
   isUnionType,
 } from "../utilities/node-types.js";
 import { stripComments } from "../utilities/strip-comments.js";
@@ -776,16 +777,19 @@ const isComplexExprNode = createTypeCheckFunction([
 /** @param {CommentContext} context */
 function handleAssignmentLikeComments(context) {
   const { comment, enclosingNode, followingNode, options, placement } = context;
-  if (isAssignmentLikeNode(enclosingNode) && followingNode) {
-    if (
-      placement === "endOfLine" &&
-      (isComplexExprNode(followingNode) || isBlockComment(comment))
-    ) {
-      return addLeadingCommentToPossibleUnionType(followingNode, context);
-    }
+  if (
+    isAssignmentLikeNode(enclosingNode) &&
+    followingNode &&
+    placement === "endOfLine" &&
+    (isComplexExprNode(followingNode) || isBlockComment(comment))
+  ) {
+    return addLeadingCommentToPossibleUnionType(followingNode, context);
+  }
 
-    // @ts-expect-error -- Safe
-    const leftSide = enclosingNode.id ?? enclosingNode.left;
+  // Ideally, we should only check cases that the right side is a single-element union or intersection type
+  // We already strip the wrapper, there is no way to know it, so we only check "type alias"
+  if (isTypeAlias(enclosingNode) && followingNode) {
+    const leftSide = enclosingNode.id;
     const equalsTokenIndex = stripComments(options).indexOf(
       "=",
       locEnd(leftSide),
diff --git a/tests/format/js/assignment-comments/__snapshots__/format.test.js.snap b/tests/format/js/assignment-comments/__snapshots__/format.test.js.snap
index a98ccfe86..30e67b19e 100644
--- a/tests/format/js/assignment-comments/__snapshots__/format.test.js.snap
+++ b/tests/format/js/assignment-comments/__snapshots__/format.test.js.snap
@@ -19,8 +19,7 @@ if (true)
     if (true)
       if (true)
         if (true)
-          longVariableName1 =
-            // @ts-ignore
+          longVariableName1 = // @ts-ignore
             (variable01 + veryLongVariableNameNumber2).method();
 
 ================================================================================
@@ -35,8 +34,7 @@ const kochabCooieGameOnOboleUnweave = // ???
       rhubarbRhubarb(annularCooeedSplicesWalksWayWay);
 
 =====================================output=====================================
-const kochabCooieGameOnOboleUnweave =
-  // ???
+const kochabCooieGameOnOboleUnweave = // ???
   rhubarbRhubarb(annularCooeedSplicesWalksWayWay);
 
 ================================================================================
@@ -123,8 +121,7 @@ f3 = (
   a = b, //comment
 ) => {};
 
-f4 =
-  // Comment
+f4 = // Comment
   () => {};
 
 f5 =
@@ -152,8 +149,7 @@ let f3 = (
   a = b, //comment
 ) => {};
 
-let f4 =
-  // Comment
+let f4 = // Comment
   () => {};
 
 let f5 =
@@ -185,12 +181,10 @@ const bifornCringerMoshedPerplexSawder = // !!!
   anodyneCondosMalateOverateRetinol;
 
 =====================================output=====================================
-const kochabCooieGameOnOboleUnweave =
-  // ???
+const kochabCooieGameOnOboleUnweave = // ???
   annularCooeedSplicesWalksWayWay;
 
-const bifornCringerMoshedPerplexSawder =
-  // !!!
+const bifornCringerMoshedPerplexSawder = // !!!
   glimseGlyphsHazardNoopsTieTie +
   averredBathersBoxroomBuggyNurl -
   anodyneCondosMalateOverateRetinol;
@@ -434,14 +428,11 @@ fnString =
   "long" +
   "string";
 
-fnString =
-  // Comment0
+fnString = // Comment0
   // Comment1
   "some" + "long" + "string";
 
-fnString =
-  // Comment
-  "some" + "long" + "string";
+fnString = "some" + "long" + "string"; // Comment
 
 fnString =
   // Comment
@@ -481,14 +472,11 @@ var fnString =
   "long" +
   "string";
 
-var fnString =
-  // Comment0
+var fnString = // Comment0
   // Comment1
   "some" + "long" + "string";
 
-var fnString =
-  // Comment
-  "some" + "long" + "string";
+var fnString = "some" + "long" + "string"; // Comment
 
 ================================================================================
 `;
diff --git a/tests/format/js/comments/assignment/__snapshots__/format.test.js.snap b/tests/format/js/comments/assignment/__snapshots__/format.test.js.snap
index 7786f4462..320f6628f 100644
--- a/tests/format/js/comments/assignment/__snapshots__/format.test.js.snap
+++ b/tests/format/js/comments/assignment/__snapshots__/format.test.js.snap
@@ -50,9 +50,7 @@ let a32 =
   /*
 commment */
   1;
-let a4 =
-  // comment
-  1;
+let a4 = 1; // comment
 let a42 =
   // comment
   1;