[WIP] allow passing a custom function as a window picker

doc/nvim-tree-lua.txt

@@ -348,6 +348,7 @@ Subsequent calls to setup will replace the previous configuration.
           resize_window = true,
           window_picker = {
             enable = true,
+            picker = "default",
             chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890",
             exclude = {
               filetype = { "notify", "packer", "qf", "diff", "fugitive", "fugitiveblame" },
@@ -999,6 +1000,16 @@ Configuration for various actions.
             from which you last opened the tree.
               Type: `boolean`, Default: `true`
 
+            *nvim-tree.actions.open_file.window_picker.picker*
+            Change the default window picker, can be a string `"default"` or a function.
+            The function should return the window id that will open the node,
+            or `nil` if an invalid window is picked or user cancelled the action.
+              Type: `string` | `function`, Default: `"default"`
+              e.g. s1n7ax/nvim-window-picker plugin: >
+                window_picker = {
+                  enable = true,
+                  picker = require('window-picker').pick_window,
+<
             *nvim-tree.actions.open_file.window_picker.chars*
             A string of chars used as identifiers by the window picker.
               Type: `string`, Default: `"ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"`

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