fix(dir): custom 3P directory-browser #40725

Problem:
Third-party directory browsers do not have a documented way to take over local
directory buffers from nvim.dir.

Solution:
Document deleting the nvim.dir augroup and handling FileType directory as the
after-startup handoff, and avoid installing the built-in buffer-local "-" mapping
when "-" is already mapped.

1 files changed, 8 insertions, 1 deletions

diff --git a/runtime/lua/nvim/dir.lua b/runtime/lua/nvim/dir.lua
index 3448fb3eab..daf5bd7a09 100644
--- a/runtime/lua/nvim/dir.lua
+++ b/runtime/lua/nvim/dir.lua
@@ -185,8 +185,15 @@ local function set_maps(buf)
       vim.keymap.set('n', lhs, plug, { buffer = buf, silent = true })
     end
   end
+  ---@param lhs string
+  ---@param plug string
+  local function default_map(lhs, plug)
+    if vim.fn.mapcheck(lhs, 'n') == '' and vim.fn.hasmapto(plug, 'n') == 0 then
+      vim.keymap.set('n', lhs, plug, { buffer = buf, silent = true })
+    end
+  end
   map('<CR>', '<Plug>(nvim-dir-open)')
-  map('-', '<Plug>(nvim-dir-up)')
+  default_map('-', '<Plug>(nvim-dir-up)')
   map('R', '<Plug>(nvim-dir-reload)')
 end