Add support for sapling SCM

This adds the ability for GFiles to return a list of files from
sapling (https://sapling-scm.org), rather than from git.

This extends git support, rather than adding a separate API for it
because the two can interoperate and it comes handy not to have to think
about the repository type of your project.

Author: ktf

autoload/fzf/vim.vim

@@ -699,11 +699,66 @@ function! s:git_version_requirement(...)
   return s:version_requirement(s:git_version, a:000)
 endfunction
 
+" Get the rootdir of sapling, i.e. the first path that contains a .sl 
+" directory.
+function! s:get_sapling_root(dir)
+  let dir = len(a:dir) ? a:dir : substitute(split(expand('%:p:h'), '[/\\]\.sl\([/\\]\|$\)')[0], '^fugitive://', '', '')
+  let root = systemlist('cd ' . fzf#shellescape(dir) . ' && sl root')[0]
+  return v:shell_error ? '' : (len(a:dir) ? fnamemodify(a:dir, ':p') : root)
+endfunction
+
+" Get the list of files from sapling
+function! s:sapling_gitfiles(args, ...)
+  let dir = get(get(a:, 1, {}), 'dir', '')
+  let root = s:get_sapling_root(dir)
+  if empty(root)
+    return s:warn('Not in git / sapling repository')
+  endif
+  if a:args != '?'
+    let prefix = 'cd ' . fzf#shellescape(root) . ' && sl '
+    echo(a:args)
+    echo(prefix)
+    let source = prefix . 'files -0 ' . a:args
+    echo(source)
+    return s:fzf('gfiles', {
+    \ 'source':  source,
+    \ 'dir':     root,
+    \ 'options': '-m --read0 --prompt "SlFiles> "'
+    \}, a:000)
+  endif
+
+  " Here be dragons!
+  " We're trying to access the common sink function that fzf#wrap injects to
+  " the options dictionary.
+  let bar = s:is_win ? '^|' : '|'
+  let diff_prefix = 'cd ' . s:escape_for_bash(root) . ' && sl '
+  let preview = printf(
+    \ s:bash() . ' -c "if [[ {1} =~ M ]]; then %s; else %s {-1}; fi"',
+    \ executable('delta')
+      \ ? diff_prefix . 'diff -- {-1} ' . bar . ' delta --width $FZF_PREVIEW_COLUMNS --file-style=omit ' . bar . ' sed 1d'
+      \ : diff_prefix . 'diff --color=always -- {-1} ' . bar . ' sed 1,4d',
+    \ s:escape_for_bash(s:bin.preview))
+  let wrapped = fzf#wrap({
+  \ 'source':  prefix . '-c color.status=always status --short --untracked-files=all',
+  \ 'dir':     root,
+  \ 'options': ['--ansi', '--multi', '--nth', '2..,..', '--tiebreak=index', '--prompt', 'GitFiles?> ', '--preview', preview]
+  \})
+  call s:remove_layout(wrapped)
+  let wrapped.common_sink = remove(wrapped, 'sink*')
+  function! wrapped.newsink(lines)
+    let lines = extend(a:lines[0:0], map(a:lines[1:], 'substitute(v:val[3:], ".* -> ", "", "")'))
+    return self.common_sink(lines)
+  endfunction
+  let wrapped['sink*'] = remove(wrapped, 'newsink')
+  return s:fzf('gfiles-diff', wrapped, a:000)
+endfunction
+
 function! fzf#vim#gitfiles(args, ...)
   let dir = get(get(a:, 1, {}), 'dir', '')
   let root = s:get_git_root(dir)
   if empty(root)
-    return s:warn('Not in git repo')
+    " Try with sapling instead
+    return call('s:sapling_gitfiles', [a:args] + a:000)
   endif
   let prefix = 'git -C ' . fzf#shellescape(root) . ' '
   if a:args != '?'