Add --porcelain=v2 status parser

New submodule modifiers:

- 'M' if submodule commit is changed, otherwise
- '?' if there is modified or untracked content

Keep using v1 parser for git versions older than 2.11. This will display
'M' for any submodule changes.

Test with https://github.com/odnoletkov/git-status-test-suite

Fixes https://github.com/tpope/vim-fugitive/issues/1204

autoload/fugitive.vim

@@ -1617,48 +1617,95 @@ function! fugitive#BufReadStatus() abort
     if s:cpath(fnamemodify($GIT_INDEX_FILE !=# '' ? $GIT_INDEX_FILE : fugitive#Find('.git/index'), ':p')) !=# s:cpath(amatch)
       let cmd += ['-c', 'GIT_INDEX_FILE=' . amatch]
     endif
-    let cmd += ['status', '--porcelain', '-bz']
-    let [output, message, exec_error] = s:NullError(cmd)
-    if exec_error
-      throw 'fugitive: ' . message
-    endif
-
-    let head = matchstr(output[0], '^## \zs\S\+\ze\%($\| \[\)')
-    let pull = ''
-    if head =~# '\.\.\.'
-      let [head, pull] = split(head, '\.\.\.')
-      let branch = head
-    elseif head ==# 'HEAD' || empty(head)
-      let head = FugitiveHead(11)
-      let branch = ''
-    else
-      let branch = head
-    endif
 
     let b:fugitive_files = {'Staged': {}, 'Unstaged': {}}
     let [staged, unstaged, untracked] = [[], [], []]
-    let i = 0
+
-    while i < len(output)
+    if fugitive#GitVersion(2, 11)
-      let line = output[i]
+      let cmd += ['status', '--porcelain=v2', '-bz']
-      let file = line[3:-1]
+      let [output, message, exec_error] = s:NullError(cmd)
-      let files = file
+      if exec_error
-      let i += 1
+        throw 'fugitive: ' . message
-      if line[2] !=# ' '
-        continue
       endif
-      if line[0:1] =~# '[RC]'
+
-        let files = output[i] . ' -> ' . file
+      let i = match(output, '^[^#]')
+      let head = matchlist(output[:i], '^# branch\.head \zs.*$')[0]
+      let pull = get(matchlist(output[:i], '^# branch\.upstream \zs.*$'), 0, '')
+      if len(pull)
+        let branch = head
+      elseif head ==# '(detached)'
+        let head = matchlist(output[:i], '^# branch\.oid \zs.*$')[0][:10]
+        let branch = ''
+      else
+        let branch = head
+      endif
+
+      while i < len(output)
+        let line = output[i]
+        if line[0] ==# '?'
+          call add(untracked, {'type': 'File', 'status': line[0], 'filename': line[2:-1]})
+        elseif line[0] !=# '#'
+          if line[0] ==# 'u'
+            let file = matchstr(line, '^.\{37\} \x\{40,\} \x\{40,\} \x\{40,\} \zs.*$')
+          else
+            let file = matchstr(line, '^.\{30\} \x\{40,\} \x\{40,\} \zs.*$')
+          endif
+          if line[0] ==# '2'
+            let i += 1
+            let file = output[i] . ' -> ' . matchstr(file, ' \zs.*')
+          endif
+          if line[2] !=# '.'
+            call add(staged, {'type': 'File', 'status': line[2], 'filename': file})
+          endif
+          if line[3] !=# '.'
+            let sub = matchstr(line, '^[12u] .. \zs....')
+            call add(unstaged, {'type': 'File', 'status': get({'C':'M','M':'?','U':'?'}, matchstr(sub, 'S\.*\zs[CMU]'), line[3]), 'filename': file})
+          endif
+        endif
         let i += 1
+      endwhile
+    else " git < 2.11
+      let cmd += ['status', '--porcelain', '-bz']
+      let [output, message, exec_error] = s:NullError(cmd)
+      if exec_error
+        throw 'fugitive: ' . message
       endif
-      if line[0] !~# '[ ?!#]'
+
-        call add(staged, {'type': 'File', 'status': line[0], 'filename': files})
+      let head = matchstr(output[0], '^## \zs\S\+\ze\%($\| \[\)')
+      let pull = ''
+      if head =~# '\.\.\.'
+        let [head, pull] = split(head, '\.\.\.')
+        let branch = head
+      elseif head ==# 'HEAD' || empty(head)
+        let head = FugitiveHead(11)
+        let branch = ''
+      else
+        let branch = head
       endif
-      if line[0:1] ==# '??'
+
-        call add(untracked, {'type': 'File', 'status': line[1], 'filename': files})
+      let i = 0
-      elseif line[1] !~# '[ !#]'
+      while i < len(output)
-        call add(unstaged, {'type': 'File', 'status': line[1], 'filename': files})
+        let line = output[i]
-      endif
+        let file = line[3:-1]
-    endwhile
+        let files = file
+        let i += 1
+        if line[2] !=# ' '
+          continue
+        endif
+        if line[0:1] =~# '[RC]'
+          let files = output[i] . ' -> ' . file
+          let i += 1
+        endif
+        if line[0] !~# '[ ?!#]'
+          call add(staged, {'type': 'File', 'status': line[0], 'filename': files})
+        endif
+        if line[0:1] ==# '??'
+          call add(untracked, {'type': 'File', 'status': line[1], 'filename': files})
+        elseif line[1] !~# '[ !#]'
+          call add(unstaged, {'type': 'File', 'status': line[1], 'filename': files})
+        endif
+      endwhile
+    endif
 
     for dict in staged
       let b:fugitive_files['Staged'][dict.filename] = dict