vim-patch:9.1.0116: win_split_ins may not check available room

Problem:  win_split_ins has no check for E36 when moving an existing
          window
Solution: check for room and fix the issues in f_win_splitmove()
          (Sean Dewar)

0fd44a5ad8

Omit WSP_FORCE_ROOM, as it's not needed for Nvim's autocmd window, which is
floating. Shouldn't be difficult to port later if it's used for anything else.

Make win_splitmove continue working for turning floating windows into splits.
Move the logic for "unfloating" a float to win_split_ins; unlike splits, no
changes to the window layout are needed before calling it, as floats take no
room in the window layout and cannot affect the e_noroom check.

Add missing tp_curwin-fixing logic for turning external windows into splits, and
add a test.
NOTE: there are other issues with the way "tabpage independence" is implemented
for external windows; namely, some things assume that tp_curwin is indeed a
window within that tabpage, and as such, functions like tabpage_winnr and
nvim_tabpage_get_win currently don't always work for external windows (with the
latter aborting!)

Use last_status over frame_add_statusline, as Nvim's last_status already does
this for all windows in the current tabpage. Adjust restore_full_snapshot_rec to
handle this.
This "restore everything" approach is changed in a future commit anyway, so only
ensure it's robust enough to just pass tests.

Keep check_split_disallowed's current doc comment, as it's actually a bit more
accurate here. (I should probably PR Vim to use this one)

Allow f_win_splitmove to move a floating "wp" into a split; Nvim supports this.
Continue to disallow it from moving the autocommand window into a split (funnily
enough, the check wasn't reachable before, as moving a float was disallowed),
but now return -1 in that case (win_splitmove also returns FAIL for this, but
handling it in f_win_splitmove avoids us needing to switch windows first).

Cherry-pick Test_window_split_no_room fix from v9.1.0121.

Update nvim_win_set_config to handle win_split_ins failure in later commits.

test/functional/ui/float_spec.lua

@@ -550,6 +550,43 @@ describe('float window', function()
     eq({ w0 }, api.nvim_list_wins())
   end)
 
+  it('win_splitmove() can move float into a split', function()
+    command('split')
+    eq({'col', {{'leaf', 1001}, {'leaf', 1000}}}, fn.winlayout())
+
+    local win1 = api.nvim_open_win(0, true, {relative = 'editor', row = 1, col = 1, width = 5, height = 5})
+    fn.win_splitmove(win1, 1001, {vertical = true})
+    eq({'col', {{'row', {{'leaf', win1}, {'leaf', 1001}}}, {'leaf', 1000}}}, fn.winlayout())
+    eq('', api.nvim_win_get_config(win1).relative)
+
+    -- Should be unable to create a split relative to a float, though.
+    local win2 = api.nvim_open_win(0, true, {relative = 'editor', row = 1, col = 1, width = 5, height = 5})
+    eq('Vim:E957: Invalid window number', pcall_err(fn.win_splitmove, win1, win2, {vertical = true}))
+  end)
+
+  it('tp_curwin updated if external window is moved into split', function()
+    local screen = Screen.new(20, 7)
+    screen:attach { ext_multigrid = true }
+
+    command('tabnew')
+    local external_win = api.nvim_open_win(0, true, {external = true, width = 5, height = 5})
+    eq(external_win, api.nvim_get_current_win())
+    eq(2, fn.tabpagenr())
+    command('tabfirst')
+    api.nvim_set_current_win(external_win)
+    eq(external_win, api.nvim_get_current_win())
+    eq(1, fn.tabpagenr())
+
+    command('wincmd J')
+    eq(external_win, api.nvim_get_current_win())
+    eq(false, api.nvim_win_get_config(external_win).external)
+    command('tabnext')
+    eq(2, fn.tabpagenr())
+    neq(external_win, api.nvim_get_current_win())
+
+    screen:detach()
+  end)
+
   describe('with only one tabpage,', function()
     local float_opts = {relative = 'editor', row = 1, col = 1, width = 1, height = 1}
     local old_buf, old_win
@@ -9101,6 +9138,22 @@ describe('float window', function()
         ]]}
       end
     end)
+
+    it('attempt to turn into split with no room', function()
+      eq('Vim(split):E36: Not enough room', pcall_err(command, 'execute "split |"->repeat(&lines)'))
+      command('vsplit | wincmd | | wincmd p')
+      api.nvim_open_win(0, true, {relative = "editor", row = 0, col = 0, width = 5, height = 5})
+      local config = api.nvim_win_get_config(0)
+      eq('editor', config.relative)
+
+      local layout = fn.winlayout()
+      local restcmd = fn.winrestcmd()
+      eq('Vim(wincmd):E36: Not enough room', pcall_err(command, 'wincmd K'))
+      eq('Vim(wincmd):E36: Not enough room', pcall_err(command, 'wincmd J'))
+      eq(layout, fn.winlayout())
+      eq(restcmd, fn.winrestcmd())
+      eq(config, api.nvim_win_get_config(0))
+    end)
   end
 
   describe('with ext_multigrid', function()