From ae43bcf68c905f7f911a3ad03ca2dbfa3f0b690c Mon Sep 17 00:00:00 2001
From: fisker Cheung <lionkay@gmail.com>
Date: Sat, 11 Oct 2025 02:58:57 +0800
Subject: [PATCH] Add tests to close issue 16121 (#18040)

---
 tests/format/typescript/comments/16121.ts     | 38 +++++++++
 .../__snapshots__/format.test.js.snap         | 85 +++++++++++++++++++
 2 files changed, 123 insertions(+)
 create mode 100644 tests/format/typescript/comments/16121.ts

diff --git a/tests/format/typescript/comments/16121.ts b/tests/format/typescript/comments/16121.ts
new file mode 100644
index 000000000..54c275371
--- /dev/null
+++ b/tests/format/typescript/comments/16121.ts
@@ -0,0 +1,38 @@
+export type IntersectionType =
+  & FirstPart
+  // Presence of comment makes this non-idempotent
+  & {
+    an: string,
+    object: string,
+    type: string,
+  }
+
+
+export type IntersectionType =
+  & FirstPart
+  // Comment Line 1
+  // Comment Line 2
+  & {
+    an: string,
+    object: string,
+    type: string,
+  }
+
+export type IntersectionType =
+  | FirstPart
+  // Presence of comment is not a problem
+  | {
+      an: string;
+      object: string;
+      type: string;
+    };
+
+export type IntersectionType =
+  | FirstPart
+  // Comment Line 1
+  // Comment Line 2
+  | {
+      an: string;
+      object: string;
+      type: string;
+    };
diff --git a/tests/format/typescript/comments/__snapshots__/format.test.js.snap b/tests/format/typescript/comments/__snapshots__/format.test.js.snap
index fb6fbbe9c..a355bf9b9 100644
--- a/tests/format/typescript/comments/__snapshots__/format.test.js.snap
+++ b/tests/format/typescript/comments/__snapshots__/format.test.js.snap
@@ -250,6 +250,91 @@ class Foo {
 ================================================================================
 `;
 
+exports[`16121.ts format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+export type IntersectionType =
+  & FirstPart
+  // Presence of comment makes this non-idempotent
+  & {
+    an: string,
+    object: string,
+    type: string,
+  }
+
+
+export type IntersectionType =
+  & FirstPart
+  // Comment Line 1
+  // Comment Line 2
+  & {
+    an: string,
+    object: string,
+    type: string,
+  }
+
+export type IntersectionType =
+  | FirstPart
+  // Presence of comment is not a problem
+  | {
+      an: string;
+      object: string;
+      type: string;
+    };
+
+export type IntersectionType =
+  | FirstPart
+  // Comment Line 1
+  // Comment Line 2
+  | {
+      an: string;
+      object: string;
+      type: string;
+    };
+
+=====================================output=====================================
+export type IntersectionType = FirstPart &
+  // Presence of comment makes this non-idempotent
+  {
+    an: string;
+    object: string;
+    type: string;
+  };
+
+export type IntersectionType = FirstPart &
+  // Comment Line 1
+  // Comment Line 2
+  {
+    an: string;
+    object: string;
+    type: string;
+  };
+
+export type IntersectionType =
+  | FirstPart
+  // Presence of comment is not a problem
+  | {
+      an: string;
+      object: string;
+      type: string;
+    };
+
+export type IntersectionType =
+  | FirstPart
+  // Comment Line 1
+  // Comment Line 2
+  | {
+      an: string;
+      object: string;
+      type: string;
+    };
+
+================================================================================
+`;
+
 exports[`16207.ts format 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]