From 71a22e20ad150fae7f42ca534e1b77208a51b83d Mon Sep 17 00:00:00 2001
From: phanium <91544758+phanen@users.noreply.github.com>
Date: Wed, 10 Dec 2025 01:32:49 +0800
Subject: [PATCH] fix: vim.ui_attach handles messages during `-l`/`--headless`
 #36884

Problem:
With vim.ui_attach in headless mode, messages are still printed.

Solution:
Don't print to stdout if a vim.ui_attach "messages" handler is defined.
---
 src/nvim/message.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/nvim/message.c b/src/nvim/message.c
index d1ac5b1960..2232784c07 100644
--- a/src/nvim/message.c
+++ b/src/nvim/message.c
@@ -2862,9 +2862,10 @@ static msgchunk_T *disp_sb_line(int row, msgchunk_T *smp)
 /// @return  true when messages should be printed to stdout/stderr:
 ///          - "batch mode" ("silent mode", -es/-Es/-l)
 ///          - no UI and not embedded
+///          - no ext_messages
 int msg_use_printf(void)
 {
-  return !embedded_mode && !ui_active();
+  return !embedded_mode && !ui_active() && !ui_has(kUIMessages);
 }
 
 /// Print a message when there is no valid screen.