fugitive compatibility for viewing commits in PlugDiff

[cpmsmith]

In :PlugDiff, it's possible to hit enter on a given commit to view its content:

fugitive.vim has a very similar feature for viewing commits, but with extra features like being able to browse to other commits and files, and with rhubarb.vim and others, to open the equivalent forge URL e.g. on GitHub.

It'd be cool if vim-plug used fugitive to view commits when it's available.

NVIM v0.9.5
Build type: Release
LuaJIT 2.1.1703358377

   system vimrc file: "$VIM/sysinit.vim"
  fall-back for $VIM: "/opt/homebrew/Cellar/neovim/0.9.5/share/nvim"

• Type:
  • [ ] Bug
  • [x] Enhancement
  • [x] Feature Request
  • [ ] Question
• OS:
  • [x] All/Other
  • [ ] Linux
  • [ ] macOS
  • [ ] Windows
• Vim:
  • [x] Terminal Vim
  • [x] GVim
  • [x] Neovim

[junegunn]

Need some more testing, but this should do the trick.

diff --git a/plug.vim b/plug.vim
index 940811a..4c3a081 100644
--- a/plug.vim
+++ b/plug.vim
@@ -2683,6 +2683,11 @@ function! s:preview_commit()
     return
   endif

+  let use_fugitive = exists('*FugitiveFind') && len(sha)
+  if use_fugitive
+    let title = FugitiveFind(sha, g:plugs[name].dir . '/.git')
+  endif
+
   if !s:is_preview_window_open()
     execute get(g:, 'plug_pwindow', 'vertical rightbelow new')
     execute 'e' title
@@ -2691,6 +2696,12 @@ function! s:preview_commit()
     wincmd P
   endif
   setlocal previewwindow filetype=git buftype=nofile bufhidden=wipe nobuflisted modifiable
+  nnoremap <silent> <buffer> q :q<cr>
+  if use_fugitive
+    wincmd p
+    return
+  endif
+
   let batchfile = ''
   try
     let [sh, shellcmdflag, shrd] = s:chsh(1)
@@ -2706,7 +2717,6 @@ function! s:preview_commit()
     endif
   endtry
   setlocal nomodifiable
-  nnoremap <silent> <buffer> q :q<cr>
   wincmd p
 endfunction

[junegunn]

The patch works. But it's considerably slower to open a commit, so users who don't need additional features of Fugitive may not like it.