fix(files): ensure current win is within explorer after closing any win

Details:
- Closing the current window will temporarily switch focus to some other
  window (probably the first "normal" window in the tabpage). This can
  be a problem since it triggers all relevant events (like `BufEnter`).
  This can manifest in directory buffer being unexpectedly closed if
  current window is at depth that will be not shown
  (`go_in`+`go_in`+`trim_left`).

  A general rule of thumb is that current window should be set before
  closing any window.

- This also removes a window close logic in explorer normalization since
  it seems to be redundant: an overlapping actions will be done later
  during explorer refresh.

Resolve #2478

Co-authored-by: abeldekat <58370433+abeldekat@users.noreply.github.com>

Author: echasnovski

lua/mini/files.lua

@@ -1569,17 +1569,18 @@ H.explorer_refresh = function(explorer, opts)
     cur_win_col = cur_win_col + cur_width + 2
   end
 
+  -- Focus on target window. Do this before closing windows to keep current
+  -- window within the explorer.
+  local win_focus_count = explorer.depth_focus - depth_range.from + 1
+  local win_id_focused = explorer.windows[win_focus_count]
+  H.window_focus(win_id_focused)
+
   -- Close possibly opened window that don't fit (like after `VimResized`)
   for depth = cur_win_count + 1, #explorer.windows do
     H.window_close(explorer.windows[depth])
     explorer.windows[depth] = nil
   end
 
-  -- Focus on proper window
-  local win_focus_count = explorer.depth_focus - depth_range.from + 1
-  local win_id_focused = explorer.windows[win_focus_count]
-  H.window_focus(win_id_focused)
-
   -- Register as currently opened
   explorer.tabpage_id = vim.api.nvim_win_get_tabpage(win_id_focused)
   H.opened_explorers[explorer.tabpage_id] = explorer
@@ -1634,17 +1635,8 @@ H.explorer_normalize = function(explorer)
     table.insert(norm_branch, path)
   end
 
-  local cur_max_depth = #norm_branch
-
   explorer.branch = norm_branch
-  explorer.depth_focus = math.min(math.max(explorer.depth_focus, 1), cur_max_depth)
-
-  -- Close all guaranteed to be unnecessary windows. NOTE: some windows might
-  -- still get outdated later if branch is too deep to fit into Neovim's width.
-  for i = cur_max_depth + 1, #explorer.windows do
-    H.window_close(explorer.windows[i])
-    explorer.windows[i] = nil
-  end
+  explorer.depth_focus = math.min(math.max(explorer.depth_focus, 1), #norm_branch)
 
   -- Compute if explorer is corrupted and should not operate further
   for _, win_id in pairs(explorer.windows) do

tests/test_files.lua

@@ -6369,6 +6369,29 @@ T['Default explorer']['handles forcing other window as current'] = function()
   if child.fn.has('nvim-0.10') == 1 then eq(child.api.nvim_get_current_win(), init_win_id) end
 end
 
+T['Default explorer']['keeps directory buffer open when number of windows decreases'] = function()
+  child.set_size(5, 90)
+  local validate = function(fn_str)
+    local test_path = make_test_path('nested')
+    child.cmd('edit ' .. test_path)
+    local dir_buf_id = child.fn.bufnr(test_path)
+
+    go_in()
+    go_in()
+    child.lua(fn_str)
+
+    -- Directory buffer should still present
+    eq(child.api.nvim_buf_is_valid(dir_buf_id), true)
+
+    -- Closing explorer should always wipeout directory buffer
+    close()
+    eq(child.api.nvim_buf_is_valid(dir_buf_id), false)
+  end
+
+  validate('MiniFiles.refresh({ windows = { max_number = 1 } })')
+  validate('MiniFiles.trim_left()')
+end
+
 T['Internal helpers'] = new_set()
 
 T['Internal helpers']['path normalization works'] = function()