From 57dc215230302f0abf0789e0e048f8d29a4e8362 Mon Sep 17 00:00:00 2001
From: Sanzhar Kuandyk <92693103+SanzharKuandyk@users.noreply.github.com>
Date: Thu, 23 Jul 2026 16:57:19 +0500
Subject: [PATCH] refactor(:restart): unnecessary console allocation on Windows
 #40919
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Problem:
`:restart` on Windows always forces `AllocConsole`, even though we could
reuse old server's existing console + unnecessary env.

Analysis:
After d5516daf121aa718e79bcd423ee24c24492893c0 changed the restart
lifecycle and 789741bb83d1f31b7162cd8944bc2d846fa2fa51 separated the
Windows console paths, we no longer need to force `AllocConsole()` for
`:restart`. The `:detach` path now allocates its own console when it
actually runs.

Solution:
Try to attach the replacement server to its parent’s console and fall
back to `AllocConsole()` if attachment fails. Drop the restart-specific
env that forced allocation.

As documented by Microsoft, [“A console is closed when the last process
attached to it terminates or calls
`FreeConsole`.”](https://learn.microsoft.com/en-us/windows/console/attachconsole)

Btw, this way we can preserve `io.stdout:write()`, though if for some
reason `AttachConsole` would fail then it won't work; but now at least
it's not always not rendering on `:restart`.
---
 src/nvim/channel.c  | 16 +++++-----------
 src/nvim/ex_docmd.c |  3 ---
 src/nvim/os/os.h    |  1 -
 3 files changed, 5 insertions(+), 15 deletions(-)

diff --git a/src/nvim/channel.c b/src/nvim/channel.c
index dcd422aa13..203bdbe680 100644
--- a/src/nvim/channel.c
+++ b/src/nvim/channel.c
@@ -563,19 +563,13 @@ uint64_t channel_from_stdio(bool rpc, CallbackReader on_output, const char **err
   if (embedded_mode && os_has_conpty_working()) {
     stdin_dup_fd = os_dup_cloexec(STDIN_FILENO);
     stdout_dup_fd = os_dup_cloexec(STDOUT_FILENO);
-    // :restart spawns a replacement server that must not borrow the parent
-    // Nvim process console, because that parent process will soon exit.
-    const bool restart_alloc_console = os_env_exists(ENV_RESTART_ALLOC_CONSOLE, true);
-    if (restart_alloc_console) {
-      os_unsetenv(ENV_RESTART_ALLOC_CONSOLE);
-    }
     if (!GetConsoleWindow()) {
       // Borrow the parent's console so CONOUT$ resolves to the real terminal,
-      // preserving io.stdout rendering (e.g. SIXEL/Kitty images). Only fall
-      // back to a hidden AllocConsole when there is no parent console (e.g.
-      // launched from a non-console parent), or for the replacement server
-      // spawned by :restart, because the parent Nvim process will soon exit.
-      if (restart_alloc_console || !AttachConsole(ATTACH_PARENT_PROCESS)) {
+      // preserving io.stdout rendering (e.g. SIXEL/Kitty images). A replacement
+      // server started by :restart can reuse the current server's console.
+      // Only fall back to a hidden console when the parent has no console.
+      if (!AttachConsole(ATTACH_PARENT_PROCESS)) {
+        ILOG("parent console attach failed: %lu; allocating hidden console", GetLastError());
         AllocConsole();
         ShowWindow(GetConsoleWindow(), SW_HIDE);
       }
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index 6cb539deb7..7dd4a108f5 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -5079,9 +5079,6 @@ static void ex_restart(exarg_T *eap)
 
   dict_T *env = create_environment(NULL, false, false, false, NULL);
   tv_dict_add_str(env, S_LEN(ENV_STARTREASON), startreason);
-#ifdef MSWIN
-  tv_dict_add_str(env, S_LEN(ENV_RESTART_ALLOC_CONSOLE), "1");
-#endif
 
   CallbackReader on_err = CALLBACK_READER_INIT;
 #ifdef MSWIN
diff --git a/src/nvim/os/os.h b/src/nvim/os/os.h
index d9677cb58b..af8872a8a5 100644
--- a/src/nvim/os/os.h
+++ b/src/nvim/os/os.h
@@ -27,6 +27,5 @@ extern char *default_lib_dir;
 #define ENV_LOGFILE "NVIM_LOG_FILE"
 #define ENV_LOGFILE_WANT "__NVIM_LOG_FILE_WANT"
 #define ENV_NVIM "NVIM"
-#define ENV_RESTART_ALLOC_CONSOLE "__NVIM_RESTART_ALLOC_CONSOLE"
 #define ENV_STARTREASON "__NVIM_STARTREASON"
 #define ENV_TEST_LOG "__NVIM_TEST_LOG"