feat(picker): allow custom function actions.open_file.window_picker.picker (#1782)

* feat: allow passing a custom function as a window picker

WIP

* fix: move logic expression to if statement

If `M.window_picker.custom_function()` returns `nil` then `pick_win_id()`
will run (the or part). We don't want that. More verbose, but better.

* feat(open): add window_picker.picker

* feat(open): add window_picker.picker

* style nit

* feat(open): add window_picker.picker

* docs: add window_picker.picker documentation

* docs: add window_picker.picker documentation

Co-authored-by: Alexander Courtis <alex@courtis.org>

lua/nvim-tree.lua

@@ -640,6 +640,7 @@ local DEFAULT_OPTS = { -- BEGIN_DEFAULT_OPTS
       resize_window = true,
       window_picker = {
         enable = true,
+        picker = "default",
         chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890",
         exclude = {
           filetype = { "notify", "packer", "qf", "diff", "fugitive", "fugitiveblame" },
@@ -699,6 +700,7 @@ local FIELD_OVERRIDE_TYPECHECK = {
   on_attach = { ["function"] = true, string = true },
   sort_by = { ["function"] = true, string = true },
   root_folder_label = { ["function"] = true, string = true },
+  picker = { ["function"] = true, string = true },
 }
 
 local function validate_options(conf)

lua/nvim-tree/actions/node/open-file.lua

@@ -175,7 +175,11 @@ local function get_target_winid(mode, win_ids)
     end
   else
     -- pick a window
-    target_winid = pick_win_id()
+    if type(M.window_picker.picker) == "function" then
+      target_winid = M.window_picker.picker()
+    else
+      target_winid = pick_win_id()
+    end
     if target_winid == nil then
       -- pick failed/cancelled
       return