[GF?] Use delta to format git diff if available

Close #1202

README.md

@@ -52,6 +52,8 @@ so you can omit it if you use a plugin manager that doesn't support hooks.
 
 - [fzf][fzf-main] 0.23.0 or above
 - For syntax-highlighted preview, install [bat](https://github.com/sharkdp/bat)
+- `:GF?` will use [delta](https://github.com/dandavison/delta) if available
+  to format `git diff` output
 - `Ag` requires [The Silver Searcher (ag)][ag]
 - `Rg` requires [ripgrep (rg)][rg]
 - `Tags` and `Helptags` require Perl

autoload/fzf/vim.vim

@@ -623,10 +623,16 @@ function! fzf#vim#gitfiles(args, ...)
   " Here be dragons!
   " We're trying to access the common sink function that fzf#wrap injects to
   " the options dictionary.
+  let preview = printf(
+    \ 'sh -c "if [[ {1} =~ M ]]; then %s; else %s {-1}; fi"',
+    \ executable('delta')
+      \ ? 'git diff -- {-1} | delta --file-style=omit | sed 1d'
+      \ : 'git diff --color=always -- {-1} | sed 1,4d',
+    \ s:bin.preview)
   let wrapped = fzf#wrap({
   \ 'source':  'git -c color.status=always status --short --untracked-files=all',
   \ 'dir':     root,
-  \ 'options': ['--ansi', '--multi', '--nth', '2..,..', '--tiebreak=index', '--prompt', 'GitFiles?> ', '--preview', 'sh -c "(git diff --color=always -- {-1} | sed 1,4d; cat {-1}) | head -1000"']
+  \ 'options': ['--ansi', '--multi', '--nth', '2..,..', '--tiebreak=index', '--prompt', 'GitFiles?> ', '--preview', preview]
   \})
   call s:remove_layout(wrapped)
   let wrapped.common_sink = remove(wrapped, 'sink*')

doc/fzf-vim.txt

@@ -1,4 +1,4 @@
-fzf-vim.txt	fzf-vim	Last change: October 22 2020
+fzf-vim.txt	fzf-vim	Last change: December 12 2020
 FZF-VIM - TABLE OF CONTENTS                                *fzf-vim* *fzf-vim-toc*
 ==============================================================================
 
@@ -92,14 +92,16 @@ so you can omit it if you use a plugin manager that doesn't support hooks.
 
  - {fzf}{1} 0.23.0 or above
  - For syntax-highlighted preview, install {bat}{5}
- - `Ag` requires {The Silver Searcher (ag)}{6}
+ - `:GF?` will use {delta}{6} if available to format `git diff` output
- - `Rg` requires {ripgrep (rg)}{7}
+ - `Ag` requires {The Silver Searcher (ag)}{7}
+ - `Rg` requires {ripgrep (rg)}{8}
  - `Tags` and `Helptags` require Perl
 
                              {1} https://github.com/junegunn/fzf
                              {5} https://github.com/sharkdp/bat
-                             {6} https://github.com/ggreer/the_silver_searcher
+                             {6} https://github.com/dandavison/delta
-                             {7} https://github.com/BurntSushi/ripgrep
+                             {7} https://github.com/ggreer/the_silver_searcher
+                             {8} https://github.com/BurntSushi/ripgrep
 
 
 COMMANDS                                                      *fzf-vim-commands*
@@ -117,8 +119,8 @@ COMMANDS                                                      *fzf-vim-commands*
   `:GFiles?`         | Git files ( `git status` )
   `:Buffers`         | Open buffers
   `:Colors`          | Color schemes
-  `:Ag [PATTERN]`    | {ag}{6} search result ( `ALT-A`  to select all,  `ALT-D`  to deselect all)
+  `:Ag [PATTERN]`    | {ag}{7} search result ( `ALT-A`  to select all,  `ALT-D`  to deselect all)
-  `:Rg [PATTERN]`    | {rg}{7} search result ( `ALT-A`  to select all,  `ALT-D`  to deselect all)
+  `:Rg [PATTERN]`    | {rg}{8} search result ( `ALT-A`  to select all,  `ALT-D`  to deselect all)
   `:Lines [QUERY]`   | Lines in loaded buffers
   `:BLines [QUERY]`  | Lines in the current buffer
   `:Tags [QUERY]`    | Tags in the project ( `ctags -R` )
@@ -129,8 +131,8 @@ COMMANDS                                                      *fzf-vim-commands*
   `:History`         |  `v:oldfiles`  and open buffers
   `:History:`        | Command history
   `:History/`        | Search history
-  `:Snippets`        | Snippets ({UltiSnips}{8})
+  `:Snippets`        | Snippets ({UltiSnips}{9})
-  `:Commits`         | Git commits (requires {fugitive.vim}{9})
+  `:Commits`         | Git commits (requires {fugitive.vim}{10})
   `:BCommits`        | Git commits for the current buffer
   `:Commands`        | Commands
   `:Maps`            | Normal mode mappings
@@ -146,14 +148,14 @@ COMMANDS                                                      *fzf-vim-commands*
  - You can set `g:fzf_command_prefix` to give the same prefix to the commands
    - e.g. `let g:fzf_command_prefix = 'Fzf'` and you have `FzfFiles`, etc.
 
-(1: `Helptags` will shadow the command of the same name from {pathogen}{10}.
+(1: `Helptags` will shadow the command of the same name from {pathogen}{11}.
 But its functionality is still available via `call pathogen#helptags()`.)
 
-                             {6} https://github.com/ggreer/the_silver_searcher
+                             {7} https://github.com/ggreer/the_silver_searcher
-                             {7} https://github.com/BurntSushi/ripgrep
+                             {8} https://github.com/BurntSushi/ripgrep
-                             {8} https://github.com/SirVer/ultisnips
+                             {9} https://github.com/SirVer/ultisnips
-                             {9} https://github.com/tpope/vim-fugitive
+                             {10} https://github.com/tpope/vim-fugitive
-                             {10} https://github.com/tpope/vim-pathogen
+                             {11} https://github.com/tpope/vim-pathogen
 
 
 CUSTOMIZATION                                            *fzf-vim-customization*
@@ -268,7 +270,7 @@ Want a preview window?
         \ call fzf#vim#files(<q-args>, {'options': ['--layout=reverse', '--info=inline', '--preview', 'cat {}']}, <bang>0)
 <
 It kind of works, but you probably want a nicer previewer program than `cat`.
-fzf.vim ships {a versatile preview script}{11} you can readily use. It
+fzf.vim ships {a versatile preview script}{12} you can readily use. It
 internally executes {bat}{5} for syntax highlighting, so make sure to install
 it.
 >
@@ -289,7 +291,7 @@ You can just omit the spec argument if you only want the previewer.
     command! -bang -nargs=? -complete=dir Files
         \ call fzf#vim#files(<q-args>, fzf#vim#with_preview(), <bang>0)
 <
-                                            {11} bin/preview.sh
+                                            {12} bin/preview.sh
                                             {5} https://github.com/sharkdp/bat
 
 
@@ -303,7 +305,7 @@ predefined `Ag` or `Rg` using `fzf#vim#grep`.
    not print column numbers.
  - We set the base directory to git root by setting `dir` attribute in spec
    dictionary.
- - {The preview script}{11} supports `grep` format (`FILE_PATH:LINE_NO:...`), so
+ - {The preview script}{12} supports `grep` format (`FILE_PATH:LINE_NO:...`), so
    we can just wrap the spec with `fzf#vim#with_preview` as before to enable
    previewer.
 >
@@ -312,7 +314,7 @@ predefined `Ag` or `Rg` using `fzf#vim#grep`.
       \   'git grep --line-number -- '.shellescape(<q-args>), 0,
       \   fzf#vim#with_preview({'dir': systemlist('git rev-parse --show-toplevel')[0]}), <bang>0)
 <
-                                                           {11} bin/preview.sh
+                                                           {12} bin/preview.sh
 
 
 Example: Rg command with preview window~
@@ -456,10 +458,10 @@ following exceptions:
 STATUS LINE OF TERMINAL BUFFER          *fzf-vim-status-line-of-terminal-buffer*
 ==============================================================================
 
-When fzf starts in a terminal buffer (see {fzf/README-VIM.md}{12}), you may
+When fzf starts in a terminal buffer (see {fzf/README-VIM.md}{13}), you may
 want to customize the statusline of the containing buffer.
 
-{12} https://github.com/junegunn/fzf/blob/master/README-VIM.md#fzf-inside-terminal-buffer
+{13} https://github.com/junegunn/fzf/blob/master/README-VIM.md#fzf-inside-terminal-buffer
 
 
 < Hide statusline >___________________________________________________________~