From c14de47f1a12e1479221ab525d224d77f7eb5953 Mon Sep 17 00:00:00 2001
From: Sean Dewar <6256228+seandewar@users.noreply.github.com>
Date: Sun, 4 Jan 2026 13:15:08 +0000
Subject: [PATCH] fix(window): crash closing only non-float if autocmds
 :tabonly (#37218)

Problem: null pointer member access when closing the only non-float in the
current tab page if autocommands after closing all floats also close all other
tab pages. (making it the last window)

Solution: check last_window again after closing the floats.

Also reduce the scope of "wp"; it would be bugprone to use it before it's later
reassigned to the rv of win_free_mem if freed by Buf/WinLeave.
---
 src/nvim/window.c                 | 15 +++++++++++----
 test/functional/ui/float_spec.lua |  5 +++++
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/nvim/window.c b/src/nvim/window.c
index 276b2a44b4..193e4757e4 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -97,6 +97,8 @@ typedef enum {
   WEE_TRIGGER_LEAVE_AUTOCMDS = 0x10,
 } wee_flags_T;
 
+static const char e_cannot_close_last_window[]
+  = N_("E444: Cannot close last window");
 static const char e_cannot_split_window_when_closing_buffer[]
   = N_("E1159: Cannot split a window when closing the buffer");
 
@@ -2710,7 +2712,7 @@ int win_close(win_T *win, bool free_buf, bool force)
   const bool had_diffmode = win->w_p_diff;
 
   if (last_window(win)) {
-    emsg(_("E444: Cannot close last window"));
+    emsg(_(e_cannot_close_last_window));
     return FAIL;
   }
 
@@ -2739,6 +2741,11 @@ int win_close(win_T *win, bool free_buf, bool force)
       if (!win_valid_any_tab(win)) {
         return FAIL;  // window already closed by autocommands
       }
+      // Autocommands may have closed all other tabpages; check again.
+      if (last_window(win)) {
+        emsg(_(e_cannot_close_last_window));
+        return FAIL;
+      }
     } else {
       emsg(e_floatonly);
       return FAIL;
@@ -2769,7 +2776,6 @@ int win_close(win_T *win, bool free_buf, bool force)
     clear_snapshot(curtab, SNAP_QUICKFIX_IDX);
   }
 
-  win_T *wp;
   bool other_buffer = false;
 
   if (win == curwin) {
@@ -2777,7 +2783,8 @@ int win_close(win_T *win, bool free_buf, bool force)
 
     // Guess which window is going to be the new current window.
     // This may change because of the autocommands (sigh).
-    wp = win->w_floating ? win_float_find_altwin(win, NULL) : frame2win(win_altframe(win, NULL));
+    win_T *wp = win->w_floating ? win_float_find_altwin(win, NULL)
+                                : frame2win(win_altframe(win, NULL));
 
     // Be careful: If autocommands delete the window or cause this window
     // to be the last one left, return now.
@@ -2872,7 +2879,7 @@ int win_close(win_T *win, bool free_buf, bool force)
   // Free the memory used for the window and get the window that received
   // the screen space.
   int dir;
-  wp = win_free_mem(win, &dir, NULL);
+  win_T *wp = win_free_mem(win, &dir, NULL);
 
   if (help_window || quickfix_window) {
     // Closing the help window moves the cursor back to the current window
diff --git a/test/functional/ui/float_spec.lua b/test/functional/ui/float_spec.lua
index ff48007543..1414e1df91 100644
--- a/test/functional/ui/float_spec.lua
+++ b/test/functional/ui/float_spec.lua
@@ -524,6 +524,11 @@ describe('float window', function()
       it('if called from non-floating window', function()
         api.nvim_set_current_win(old_win)
         eq('Vim:E444: Cannot close last window', pcall_err(api.nvim_win_close, old_win, false))
+        -- Start with many tab pages, but make autocommands from closing floats leave us with just
+        -- one (where we're now the last window).
+        command('tabnew | autocmd WinClosed * ++once tabonly')
+        api.nvim_open_win(0, false, float_opts)
+        eq('Vim:E444: Cannot close last window', pcall_err(api.nvim_win_close, 0, true))
       end)
       it('if called from floating window', function()
         eq('Vim:E444: Cannot close last window', pcall_err(api.nvim_win_close, old_win, false))