fix(api): win_set_config autocmds crash when moving win to other tabpage

Problem: win_enter autocommands can close new_curwin, crashing if it was the
last window in its tabpage after removing win, or can close parent, crashing
when attempting to split it later.

Solution: remove win first, check that parent is valid after win_enter.

NOTE: This isn't actually quite right, as this means win is not in the window
list or even has a frame when triggering enter autocommands (so it's not
considered valid in the tabpage). This is addressed in later commits.

1 files changed, 21 insertions, 0 deletions

diff --git a/test/functional/api/window_spec.lua b/test/functional/api/window_spec.lua
index 097a546ef2..a812d502eb 100644
--- a/test/functional/api/window_spec.lua
+++ b/test/functional/api/window_spec.lua
@@ -1663,6 +1663,27 @@ describe('API/win', function()
         },
       }, fn.winlayout())
     end)
+
+    it('closing new curwin when moving window to other tabpage works', function()
+      command('split | tabnew')
+      local w = api.nvim_get_current_win()
+      local t = api.nvim_get_current_tabpage()
+      command('tabfirst | autocmd WinEnter * ++once quit')
+      api.nvim_win_set_config(0, { win = w, split = 'left' })
+      -- New tabpage is now the only one, as WinEnter closed the new curwin in the original.
+      eq(t, api.nvim_get_current_tabpage())
+      eq({ t }, api.nvim_list_tabpages())
+    end)
+
+    it('closing split parent when moving window to other tabpage aborts', function()
+      command('split | tabnew')
+      local w = api.nvim_get_current_win()
+      command('tabfirst | autocmd WinEnter * call nvim_win_close(' .. w .. ', 1)')
+      eq(
+        'Window to split was closed',
+        pcall_err(api.nvim_win_set_config, 0, { win = w, split = 'left' })
+      )
+    end)
   end)
 
   describe('get_config', function()