vimrc: Use Gundo when -python3 and Undotree when +python3

I got this error today when opening Gundo:

    "__Gundo__" [New File]
    Error detected while processing function gundo#GundoToggle[1]..<SNR>102_GundoToggle[6]..<SNR>102_GundoOpen[31]..<SNR>102_GundoRenderPreview:
    line    2:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "HOME/.vim/bundle/gundo/autoload/gundo.py", line 474, in GundoRenderPreview
        _output_preview_text(_generate_preview_diff(current, node_before, node_after))
      File "HOME/.vim/bundle/gundo/autoload/gundo.py", line 382, in _generate_preview_diff
        before_time, after_time))
      File "/usr/local/opt/python/Frameworks/Python.framework/Versions/3.7/lib/python3.7/difflib.py", line 1177, in unified_diff
        _check_types(a, b, fromfile, tofile, fromfiledate, tofiledate, lineterm)
      File "/usr/local/opt/python/Frameworks/Python.framework/Versions/3.7/lib/python3.7/difflib.py", line 1312, in _check_types
        raise TypeError('all arguments must be str, not: %r' % (arg,))
    TypeError: all arguments must be str, not: 74

Didn't really want to bother investigating, so I tried Undotree and it
worked. Since I have different Vims on different machines, keep Gundo as
before, but use Undotree instead when compiled with +python3.

1 files changed, 11 insertions, 3 deletions

diff --git a/vimrc b/vimrc
index f2c62ab..9265b86 100644
--- a/vimrc
+++ b/vimrc
@@ -419,6 +419,9 @@
 "       * Add `<leader>tc` mapping to close current tab.
 "       * Turn on 'undofile' for persistent undo.
 "
+"   2019.06.03:
+"       * Use Gundo when -python3 and Undotree when +python3.
+"
 
 
 " Pathogen
@@ -605,10 +608,15 @@ if exists('g:colors_name') && g:colors_name ==# 'twilight256'
 endif
 
 
-" Gundo
-nnoremap <leader>gu :GundoToggle<cr>
+" Gundo / Undotree
 if has('python3')
-	let g:gundo_prefer_python3 = 1
+	let loaded_gundo = 1
+
+	nnoremap <leader>gu :UndotreeToggle<cr>
+else
+	let g:loaded_undotree = 1
+
+	nnoremap <leader>gu :GundoToggle<cr>
 endif