fix(window): don't enter unfocusable or hidden prevwin (#34486)

Problem:  When closing a floating window, the next window to be entered
          may be unfocusable or hidden.
Solution: Don't enter prevwin when it is unfocusable or hidden. Enter
          firstwin instead (like for when prevwin is no longer valid).
(cherry picked from commit 0d658660c2)

src/nvim/window.c

@@ -2741,15 +2741,7 @@ 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).
-    if (!win->w_floating) {
+    wp = win->w_floating ? win_float_find_altwin(win, NULL) : frame2win(win_altframe(win, NULL));
-      wp = frame2win(win_altframe(win, NULL));
-    } else {
-      if (win_valid(prevwin) && prevwin != win) {
-        wp = prevwin;
-      } else {
-        wp = firstwin;
-      }
-    }
 
     // Be careful: If autocommands delete the window or cause this window
     // to be the last one left, return now.

src/nvim/winfloat.c

@@ -367,13 +367,15 @@ win_T *win_float_find_preview(void)
 win_T *win_float_find_altwin(const win_T *win, const tabpage_T *tp)
   FUNC_ATTR_NONNULL_ARG(1)
 {
+  win_T *wp = prevwin;
   if (tp == NULL) {
-    return (win_valid(prevwin) && prevwin != win) ? prevwin : firstwin;
+    return (win_valid(wp) && wp != win && wp->w_config.focusable
+            && !wp->w_config.hide) ? wp : firstwin;
   }
 
   assert(tp != curtab);
-  return (tabpage_win_valid(tp, tp->tp_prevwin) && tp->tp_prevwin != win) ? tp->tp_prevwin
+  wp = tabpage_win_valid(tp, tp->tp_prevwin) ? tp->tp_prevwin : tp->tp_firstwin;
-                                                                          : tp->tp_firstwin;
+  return (wp->w_config.focusable && !wp->w_config.hide) ? wp : tp->tp_firstwin;
 }
 
 /// Inline helper function for handling errors and cleanup in win_float_create.

test/functional/api/window_spec.lua

@@ -745,6 +745,32 @@ describe('API/win', function()
       eq(prevwin, api.nvim_tabpage_get_win(tab))
       assert_alive()
     end)
+
+    it('closing a float does not enter unfocusable or hidden prevwin', function()
+      local firstwin = api.nvim_get_current_win()
+      local wins = {} ---@type integer[]
+      for _ = 1, 4 do
+        wins[#wins + 1] = api.nvim_open_win(0, true, {
+          relative = 'editor',
+          row = 10,
+          col = 10,
+          width = 50,
+          height = 10,
+        })
+      end
+      api.nvim_win_set_config(wins[3], { hide = true })
+      api.nvim_win_close(0, false)
+      eq(firstwin, api.nvim_get_current_win())
+      api.nvim_set_current_win(wins[2])
+      api.nvim_set_current_win(wins[3])
+      api.nvim_win_set_config(wins[2], { focusable = false })
+      api.nvim_win_close(0, false)
+      eq(firstwin, api.nvim_get_current_win())
+      api.nvim_set_current_win(wins[1])
+      api.nvim_set_current_win(wins[2])
+      api.nvim_win_close(0, false)
+      eq(wins[1], api.nvim_get_current_win())
+    end)
   end)
 
   describe('hide', function()