From c5a3c5f8ce539a23e4ad14a6cdd9461ade79b748 Mon Sep 17 00:00:00 2001
From: Tim Pope <code@tpope.net>
Date: Sat, 21 Jun 2014 08:18:46 -0400
Subject: [PATCH] Smart choice of vertical or horizontal diff

---
 doc/fugitive.txt    | 10 ++++++----
 plugin/fugitive.vim | 12 +++++++++++-
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/doc/fugitive.txt b/doc/fugitive.txt
index 6397209..5e0a3a4 100644
--- a/doc/fugitive.txt
+++ b/doc/fugitive.txt
@@ -149,14 +149,16 @@ that are part of Git repositories).
                         index is used (which means a three-way diff during a
                         merge conflict, making it a git-mergetool
                         alternative).  The newer of the two files is placed
-                        to the right.  Use |do| and |dp| and write to the
-                        index file to simulate "git add --patch".
+                        to the right or bottom, depending on 'diffopt' and
+                        the width of the window relative to 'textwidth'.  Use
+                        |do| and |dp| and write to the index file to simulate
+                        "git add --patch".
 
                                                 *fugitive-:Gsdiff*
-:Gsdiff [revision]      Like |:Gdiff|, but split horizontally.
+:Gsdiff [revision]      Like |:Gdiff|, but always split horizontally.
 
                                                 *fugitive-:Gvdiff*
-:Gvdiff [revision]      Identical to |:Gdiff|.  For symmetry with |:Gsdiff|.
+:Gvdiff [revision]      Like |:Gdiff|, but always split vertically.
 
                                                 *fugitive-:Gmove*
 :Gmove {destination}    Wrapper around git-mv that renames the buffer
diff --git a/plugin/fugitive.vim b/plugin/fugitive.vim
index cbb7b71..4d0edd1 100644
--- a/plugin/fugitive.vim
+++ b/plugin/fugitive.vim
@@ -1386,7 +1386,7 @@ endfunction
 " }}}1
 " Gdiff {{{1
 
-call s:command("-bang -bar -nargs=* -complete=customlist,s:EditComplete Gdiff :execute s:Diff(<bang>0,<f-args>)")
+call s:command("-bang -bar -nargs=* -complete=customlist,s:EditComplete Gdiff :execute s:Diff(s:diff_horizontal(),<f-args>)")
 call s:command("-bar -nargs=* -complete=customlist,s:EditComplete Gvdiff :execute s:Diff(0,<f-args>)")
 call s:command("-bar -nargs=* -complete=customlist,s:EditComplete Gsdiff :execute s:Diff(1,<f-args>)")
 
@@ -1406,6 +1406,16 @@ augroup fugitive_diff
         \ endif
 augroup END
 
+function! s:diff_horizontal() abort
+  if &diffopt =~# 'horizontal' && &diffopt !~# 'vertical'
+    return 1
+  elseif &diffopt =~# 'vertical'
+    return 0
+  else
+    return winwidth(0) <= 2 * (&tw ? &tw : 80)
+  endif
+endfunction
+
 function! s:diff_window_count() abort
   let c = 0
   for nr in range(1,winnr('$'))