Introduce helper to normalize to backslashes on win32

FugitiveVimPath() is intended to potentially convert between UNIX and
Windows paths in mixed environments.  Let's separate uses that require
that from those that simply normalize slashes.

autoload/fugitive.vim

@@ -139,15 +139,29 @@ function! s:Mods(mods, ...) abort
 endfunction
 
 if exists('+shellslash')
+
   let s:dir_commit_file = '\c^fugitive://\%(/\a\@=\)\=\(.\{-\}\)//\%(\(\x\{40,\}\|[0-3]\)\(/.*\)\=\)\=$'
+
   function! s:Slash(path) abort
     return tr(a:path, '\', '/')
   endfunction
+
+  function! s:VimSlash(path) abort
+    return tr(a:path, '\/', &shellslash ? '//' : '\\')
+  endfunction
+
 else
+
   let s:dir_commit_file = '\c^fugitive://\(.\{-\}\)//\%(\(\x\{40,\}\|[0-3]\)\(/.*\)\=\)\=$'
+
   function! s:Slash(path) abort
     return a:path
   endfunction
+
+  function! s:VimSlash(path) abort
+    return a:path
+  endfunction
+
 endif
 
 function! s:AbsoluteVimPath(...) abort
@@ -169,7 +183,7 @@ endfunction
 function! s:Resolve(path) abort
   let path = resolve(a:path)
   if has('win32')
-    let path = FugitiveVimPath(fnamemodify(fnamemodify(path, ':h'), ':p') . fnamemodify(path, ':t'))
+    let path = s:VimSlash(fnamemodify(fnamemodify(path, ':h'), ':p') . fnamemodify(path, ':t'))
   endif
   return path
 endfunction
@@ -181,9 +195,9 @@ endfunction
 
 function! s:cpath(path, ...) abort
   if s:FileIgnoreCase(0)
-    let path = FugitiveVimPath(tolower(a:path))
+    let path = s:VimSlash(tolower(a:path))
   else
-    let path = FugitiveVimPath(a:path)
+    let path = s:VimSlash(a:path)
   endif
   return a:0 ? path ==# s:cpath(a:1) : path
 endfunction
@@ -433,7 +447,7 @@ endfunction
 
 function! s:UserCommandCwd(dir) abort
   let tree = s:Tree(a:dir)
-  return len(tree) ? FugitiveVimPath(tree) : getcwd()
+  return len(tree) ? s:VimSlash(tree) : getcwd()
 endfunction
 
 function! s:UserCommandList(...) abort
@@ -728,7 +742,7 @@ function! fugitive#PrepareJob(...) abort
     let dict.cwd = getcwd()
     call extend(cmd, ['--git-dir=' . FugitiveGitPath(dir)], 'keep')
   else
-    let dict.cwd = FugitiveVimPath(tree)
+    let dict.cwd = s:VimSlash(tree)
     call extend(cmd, ['-C', FugitiveGitPath(tree)], 'keep')
     if !s:cpath(tree . '/.git', dir) || len($GIT_DIR)
       call extend(cmd, ['--git-dir=' . FugitiveGitPath(dir)], 'keep')
@@ -1674,7 +1688,7 @@ function! fugitive#Real(url) abort
   let [dir, commit, file] = s:DirCommitFile(a:url)
   if len(dir)
     let tree = s:Tree(dir)
-    return FugitiveVimPath((len(tree) ? tree : s:GitDir(dir)) . file)
+    return s:VimSlash((len(tree) ? tree : s:GitDir(dir)) . file)
   endif
   let pre = substitute(matchstr(a:url, '^\a\a\+\ze:'), '^.', '\u&', '')
   if len(pre) && pre !=? 'fugitive' && exists('*' . pre . 'Real')
@@ -1682,7 +1696,7 @@ function! fugitive#Real(url) abort
   else
     let url = fnamemodify(a:url, ':p' . (a:url =~# '[\/]$' ? '' : ':s?[\/]$??'))
   endif
-  return FugitiveVimPath(empty(url) ? a:url : url)
+  return s:VimSlash(empty(url) ? a:url : url)
 endfunction
 
 function! fugitive#Path(url, ...) abort
@@ -1742,17 +1756,17 @@ endfunction
 function! fugitive#Find(object, ...) abort
   if type(a:object) == type(0)
     let name = bufname(a:object)
-    return FugitiveVimPath(name =~# '^$\|^/\|^\a\+:' ? name : getcwd() . '/' . name)
+    return s:VimSlash(name =~# '^$\|^/\|^\a\+:' ? name : getcwd() . '/' . name)
   elseif a:object =~# '^[~$]'
     let prefix = matchstr(a:object, '^[~$]\i*')
     let owner = expand(prefix)
-    return FugitiveVimPath((len(owner) ? owner : prefix) . strpart(a:object, len(prefix)))
+    return s:VimSlash(FugitiveVimPath((len(owner) ? owner : prefix) . strpart(a:object, len(prefix))))
   endif
   let rev = s:Slash(a:object)
   if rev =~# '^$\|^/\|^\%(\a\a\+:\).*\%(//\|::\)' . (has('win32') ? '\|^\a:/' : '')
-    return FugitiveVimPath(a:object)
+    return s:VimSlash(a:object)
   elseif rev =~# '^\.\.\=\%(/\|$\)'
-    return FugitiveVimPath(simplify(getcwd() . '/' . a:object))
+    return s:VimSlash(simplify(getcwd() . '/' . a:object))
   endif
   let dir = call('s:GitDir', a:000)
   if empty(dir)
@@ -1778,7 +1792,7 @@ function! fugitive#Find(object, ...) abort
     elseif cdir !=# fdir && (
           \ f =~# '^\%(config\|hooks\|info\|logs/refs\|objects\|refs\|worktrees\)\%(/\|$\)' ||
           \ f !~# '^\%(index$\|index\.lock$\|\w*MSG$\|\w*HEAD$\|logs/\w*HEAD$\|logs$\|rebase-\w\+\)\%(/\|$\)' &&
-          \ getftime(FugitiveVimPath(fdir . f)) < 0 && getftime(FugitiveVimPath(cdir . f)) >= 0)
+          \ getftime(fdir . f) < 0 && getftime(cdir . f) >= 0)
       let f = simplify(cdir . f)
     else
       let f = simplify(fdir . f)
@@ -1859,7 +1873,7 @@ function! fugitive#Find(object, ...) abort
       endif
     endif
   endif
-  return FugitiveVimPath(f)
+  return s:VimSlash(f)
 endfunction
 
 function! s:Generate(object, ...) abort
@@ -1868,10 +1882,10 @@ function! s:Generate(object, ...) abort
   if !empty(f)
     return f
   elseif a:object ==# ':/'
-    return len(dir) ? FugitiveVimPath(s:DirUrlPrefix(dir) . '0') : '.'
+    return len(dir) ? s:VimSlash(s:DirUrlPrefix(dir) . '0') : '.'
   endif
   let file = matchstr(a:object, '^\%(:\d:\|[^:]*:\)\zs.*')
-  return fnamemodify(FugitiveVimPath(len(file) ? file : a:object), ':p')
+  return fnamemodify(s:VimSlash(len(file) ? file : a:object), ':p')
 endfunction
 
 function! s:DotRelative(path, ...) abort
@@ -2126,11 +2140,11 @@ function! fugitive#simplify(url) abort
     if len(tree)
       let path = simplify(tree . file)
       if strpart(path . '/', 0, len(tree) + 1) !=# tree . '/'
-        return FugitiveVimPath(path)
+        return s:VimSlash(path)
       endif
     endif
   endif
-  return FugitiveVimPath('fugitive://' . simplify(dir) . '//' . commit . simplify(file))
+  return s:VimSlash('fugitive://' . simplify(dir) . '//' . commit . simplify(file))
 endfunction
 
 function! fugitive#resolve(url) abort
@@ -2308,7 +2322,7 @@ function! fugitive#glob(url, ...) abort
     call filter(files, 'v:val =~# pattern')
     let prepend = s:DirUrlPrefix(dir) . substitute(commit, '^:', '', '') . '/'
     call sort(files)
-    call map(files, 'FugitiveVimPath(prepend . v:val . append)')
+    call map(files, 's:VimSlash(prepend . v:val . append)')
     call extend(results, files)
   endfor
   if a:0 > 1 && a:2
@@ -3274,8 +3288,8 @@ augroup END
 function! s:AskPassArgs(dir) abort
   if (len($DISPLAY) || len($TERM_PROGRAM) || has('gui_running')) &&
         \ empty($GIT_ASKPASS) && empty($SSH_ASKPASS) && empty(fugitive#ConfigGetAll('core.askpass', a:dir))
-    if s:executable(FugitiveVimPath(s:ExecPath() . '/git-gui--askpass'))
+    if s:executable(s:VimExecPath() . '/git-gui--askpass')
-      return ['-c', 'core.askPass=' . s:ExecPath() . '/git-gui--askpass']
+      return ['-c', 'core.askPass=' . s:ExecPath()[0] . '/git-gui--askpass']
     elseif s:executable('ssh-askpass')
       return ['-c', 'core.askPass=ssh-askpass']
     endif
@@ -3709,8 +3723,8 @@ function! fugitive#Command(line1, line2, range, bang, mods, arg, ...) abort
     return (empty(cmd) ? 'exe' : cmd) . after
   endif
   let alias = FugitiveConfigGet('alias.' . get(args, 0, ''), config)
-  if get(args, 1, '') !=# '--help' && alias !~# '^$\|^!\|[\"'']' && !filereadable(FugitiveVimPath(s:ExecPath() . '/git-' . args[0]))
+  if get(args, 1, '') !=# '--help' && alias !~# '^$\|^!\|[\"'']' && !filereadable(s:VimExecPath() . '/git-' . args[0])
-        \ && !(has('win32') && filereadable(FugitiveVimPath(s:ExecPath() . '/git-' . args[0] . '.exe')))
+        \ && !(has('win32') && filereadable(s:VimExecPath() . '/git-' . args[0] . '.exe'))
     call remove(args, 0)
     call extend(args, split(alias, '\s\+'), 'keep')
   endif
@@ -3923,11 +3937,16 @@ let s:exec_paths = {}
 function! s:ExecPath() abort
   let git = s:GitShellCmd()
   if !has_key(s:exec_paths, git)
-    let s:exec_paths[git] = get(s:JobExecute(s:GitCmd() + ['--exec-path'], {}, [], [], {}).stdout, 0, '')
+    let path = get(s:JobExecute(s:GitCmd() + ['--exec-path'], {}, [], [], {}).stdout, 0, '')
+    let s:exec_paths[git] = [path, FugitiveVimPath(path)]
   endif
   return s:exec_paths[git]
 endfunction
 
+function! s:VimExecPath() abort
+  return s:ExecPath()[1]
+endfunction
+
 let s:subcommands_before_2_5 = [
       \ 'add', 'am', 'apply', 'archive', 'bisect', 'blame', 'branch', 'bundle',
       \ 'checkout', 'cherry', 'cherry-pick', 'citool', 'clean', 'clone', 'commit', 'config',
@@ -3940,7 +3959,7 @@ let s:subcommands_before_2_5 = [
       \ ]
 let s:path_subcommands = {}
 function! s:CompletableSubcommands(dir) abort
-  let c_exec_path = s:cpath(s:ExecPath())
+  let c_exec_path = s:cpath(s:VimExecPath())
   if !has_key(s:path_subcommands, c_exec_path)
     if fugitive#GitVersion(2, 18)
       let [lines, exec_error] = s:LinesError([a:dir, '--list-cmds=list-mainporcelain,nohelpers,list-complete'])
@@ -4035,7 +4054,7 @@ function! fugitive#Cd(path, ...) abort
     exe s:DirCheck(dir)
     let path = (empty(s:Tree(dir)) ? dir : s:Tree(dir)) . '/' . path
   endif
-  return (a:0 && a:1 ? 'lcd ' : 'cd ') . s:fnameescape(FugitiveVimPath(path))
+  return (a:0 && a:1 ? 'lcd ' : 'cd ') . fnameescape(s:VimSlash(path))
 endfunction
 
 " Section: :Gstatus
@@ -4955,13 +4974,13 @@ function! s:StageDelete(lnum1, lnum2, count) abort
         call s:TreeChomp('clean', '-f', '--', info.paths[0])
       elseif a:count == 2
         if get(b:fugitive_files['Staged'], info.filename, {'status': ''}).status ==# 'D'
-          call delete(FugitiveVimPath(info.paths[0]))
+          call delete(info.paths[0])
         else
           call s:TreeChomp('checkout', '--ours', '--', info.paths[0])
         endif
       elseif a:count == 3
         if get(b:fugitive_files['Unstaged'], info.filename, {'status': ''}).status ==# 'D'
-          call delete(FugitiveVimPath(info.paths[0]))
+          call delete(info.paths[0])
         else
           call s:TreeChomp('checkout', '--theirs', '--', info.paths[0])
         endif
@@ -4977,7 +4996,7 @@ function! s:StageDelete(lnum1, lnum2, count) abort
           continue
         endif
       elseif info.status ==# 'U'
-        call delete(FugitiveVimPath(info.paths[0]))
+        call delete(info.paths[0])
       elseif info.status ==# 'A'
         call s:TreeChomp('rm', '-f', '--', info.paths[0])
       elseif info.section ==# 'Unstaged'
@@ -5336,7 +5355,7 @@ function! s:ToolItems(state, from, to, offsets, text, ...) abort
     endif
     let item = {
           \ 'valid': a:0 ? a:1 : 1,
-          \ 'filename': diff.filename . FugitiveVimPath(path),
+          \ 'filename': diff.filename . s:VimSlash(path),
           \ 'lnum': matchstr(get(a:offsets, i), '\d\+'),
           \ 'text': a:text}
     if len(get(diff, 'module', ''))
@@ -5626,7 +5645,7 @@ function! s:GrepOptions(args, dir) abort
   let options = {'name_only': 0, 'name_count': 0, 'line_number': 0}
   let tree = s:Tree(a:dir)
   let prefix = empty(tree) ? fugitive#Find(':0:', a:dir) :
-        \ s:cpath(getcwd(), tree) ? '' : FugitiveVimPath(tree . '/')
+        \ s:cpath(getcwd(), tree) ? '' : s:VimSlash(tree . '/')
   let options.prefix = prefix
   for arg in a:args
     if arg ==# '--'
@@ -5850,7 +5869,7 @@ function! s:LogParse(state, dir, prefix, line) abort
       call add(a:state.queue, {
             \ 'valid': 1,
             \ 'context': context,
-            \ 'filename': FugitiveVimPath(a:state.base . '/' . a:state.to),
+            \ 'filename': s:VimSlash(a:state.base . '/' . a:state.to),
             \ 'module': a:state.base_module . ':' . a:state.to,
             \ 'lnum': offsets[-1],
             \ 'text': a:state.message . matchstr(a:line, ' @@\+ .\+')})
@@ -6551,7 +6570,7 @@ function! fugitive#Diffsplit(autodir, keepfocus, mods, arg, ...) abort
     endif
     let spec = s:Generate(file)
     if spec =~# '^fugitive:' && empty(s:DirCommitFile(spec)[2])
-      let spec = FugitiveVimPath(spec . s:Relative('/'))
+      let spec = s:VimSlash(spec . s:Relative('/'))
     endif
     exe pre
     let restore = s:diff_restore()

plugin/fugitive.vim

@@ -58,7 +58,7 @@ function! FugitiveReal(...) abort
   if type(file) ==# type({})
     let dir = FugitiveGitDir(file)
     let tree = s:Tree(dir)
-    return FugitiveVimPath(empty(tree) ? dir : tree)
+    return s:VimSlash(empty(tree) ? dir : tree)
   elseif file =~# '^\a\a\+:' || a:0 > 1
     return call('fugitive#Real', [file] + a:000[1:-1])
   elseif file =~# '^/\|^\a:\|^$'
@@ -490,28 +490,42 @@ function! FugitiveDetect(...) abort
   return ''
 endfunction
 
-function! FugitiveVimPath(path) abort
-  if exists('+shellslash') && !&shellslash
-    return tr(a:path, '/', '\')
-  else
-    return a:path
-  endif
-endfunction
-
 function! FugitiveGitPath(path) abort
   return s:Slash(a:path)
 endfunction
 
 if exists('+shellslash')
+
   let s:dir_commit_file = '\c^fugitive://\%(/\a\@=\)\=\(.\{-\}\)//\%(\(\x\{40,\}\|[0-3]\)\(/.*\)\=\)\=$'
+
   function! s:Slash(path) abort
     return tr(a:path, '\', '/')
   endfunction
+
+  function! s:VimSlash(path) abort
+    return tr(a:path, '\/', &shellslash ? '//' : '\\')
+  endfunction
+
+  function FugitiveVimPath(path) abort
+    return tr(a:path, '\/', &shellslash ? '//' : '\\')
+  endfunction
+
 else
+
   let s:dir_commit_file = '\c^fugitive://\(.\{-\}\)//\%(\(\x\{40,\}\|[0-3]\)\(/.*\)\=\)\=$'
+
   function! s:Slash(path) abort
     return a:path
   endfunction
+
+  function! s:VimSlash(path) abort
+    return a:path
+  endfunction
+
+  function! FugitiveVimPath(path) abort
+    return a:path
+  endfunction
+
 endif
 
 function! s:ProjectionistDetect() abort