From 6bc99db278c8acf5b0c12eb37527cb5e4a429c84 Mon Sep 17 00:00:00 2001
From: fisker Cheung <lionkay@gmail.com>
Date: Mon, 21 Sep 2026 23:20:48 +0800
Subject: [PATCH] Prevent comment after head of member chain move around
 (#20125)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
---
 changelog_unreleased/javascript/20125.md      | 15 +++++++++++
 src/language-js/print/member-chain.js         | 11 ++++----
 .../__snapshots__/format.test.js.snap         | 27 +++++++++++++++++++
 tests/format/js/method-chain/issue-18523.js   |  8 ++++++
 4 files changed, 56 insertions(+), 5 deletions(-)
 create mode 100644 changelog_unreleased/javascript/20125.md
 create mode 100644 tests/format/js/method-chain/issue-18523.js

diff --git a/changelog_unreleased/javascript/20125.md b/changelog_unreleased/javascript/20125.md
new file mode 100644
index 000000000..80231abd1
--- /dev/null
+++ b/changelog_unreleased/javascript/20125.md
@@ -0,0 +1,15 @@
+#### Prevent comment after head of member chain move around (#20125 by @fisker)
+
+<!-- prettier-ignore -->
+```jsx
+// Input
+x // comment
+  .foo()
+
+// Prettier stable
+x.foo(); // comment
+
+// Prettier main
+x // comment
+  .foo();
+```
diff --git a/src/language-js/print/member-chain.js b/src/language-js/print/member-chain.js
index 284025500..d43be4f57 100644
--- a/src/language-js/print/member-chain.js
+++ b/src/language-js/print/member-chain.js
@@ -293,11 +293,12 @@ function printMemberChain(path, options, print) {
     if (groups[0].length === 1) {
       const firstNode = groups[0][0].node;
       return (
-        firstNode.type === "ThisExpression" ||
-        (firstNode.type === "Identifier" &&
-          (isFactory(firstNode.name) ||
-            (isExpressionStatement && isShort(firstNode.name)) ||
-            hasComputed))
+        (firstNode.type === "ThisExpression" ||
+          (firstNode.type === "Identifier" &&
+            (isFactory(firstNode.name) ||
+              (isExpressionStatement && isShort(firstNode.name)) ||
+              hasComputed))) &&
+        !hasComment(firstNode, CommentCheckFlags.Trailing)
       );
     }
 
diff --git a/tests/format/js/method-chain/__snapshots__/format.test.js.snap b/tests/format/js/method-chain/__snapshots__/format.test.js.snap
index e920577c9..4132e915e 100644
--- a/tests/format/js/method-chain/__snapshots__/format.test.js.snap
+++ b/tests/format/js/method-chain/__snapshots__/format.test.js.snap
@@ -1281,6 +1281,33 @@ s.get(u)?.trigger({
 ================================================================================
 `;
 
+exports[`issue-18523.js format 1`] = `
+====================================options=====================================
+parsers: ["babel", "flow", "typescript"]
+                                                      printWidth: 80 (default) |
+=====================================input======================================
+a //
+  .bla()
+
+abc //
+  .bla()
+
+this //
+  .bla()
+
+=====================================output=====================================
+a //
+  .bla();
+
+abc //
+  .bla();
+
+this //
+  .bla();
+
+================================================================================
+`;
+
 exports[`logical.js format 1`] = `
 ====================================options=====================================
 parsers: ["babel", "flow", "typescript"]
diff --git a/tests/format/js/method-chain/issue-18523.js b/tests/format/js/method-chain/issue-18523.js
new file mode 100644
index 000000000..b341df910
--- /dev/null
+++ b/tests/format/js/method-chain/issue-18523.js
@@ -0,0 +1,8 @@
+a //
+  .bla()
+
+abc //
+  .bla()
+
+this //
+  .bla()