Heeds git's "assume unchanged" bit

I.e. does not diff files which should be assumed unchanged.

See:

    git update-index --[no-]assume-unchanged -- <file>
    git ls-files -v

Closes #826.

README.mkd

@@ -18,6 +18,7 @@ Features:
 * Stage partial hunks.
 * Provides a hunk text object.
 * Diffs against index (default) or any commit.
+* Heeds git's "assume unchanged" bit.
 * Allows folding all unchanged text.
 * Provides fold text showing whether folded lines have been changed.
 * Can load all hunk locations into quickfix list or the current window's location list.

autoload/gitgutter.vim

@@ -44,6 +44,8 @@ function! gitgutter#process_buffer(bufnr, force) abort
         let diff = gitgutter#diff#run_diff(a:bufnr, g:gitgutter_diff_relative_to, 0)
       catch /gitgutter not tracked/
         call gitgutter#debug#log('Not tracked: '.gitgutter#utility#file(a:bufnr))
+      catch /gitgutter assume unchanged/
+        call gitgutter#debug#log('Assume unchanged: '.gitgutter#utility#file(a:bufnr))
       catch /gitgutter diff failed/
         call gitgutter#debug#log('Diff failed: '.gitgutter#utility#file(a:bufnr))
         call gitgutter#hunk#reset(a:bufnr)

autoload/gitgutter/diff.vim

@@ -77,6 +77,10 @@ function! gitgutter#diff#run_diff(bufnr, from, preserve_full_diff) abort
     throw 'gitgutter not tracked'
   endif
 
+  if gitgutter#utility#repo_path(a:bufnr, 0) == -3
+    throw 'gitgutter assume unchanged'
+  endif
+
   " Wrap compound commands in parentheses to make Windows happy.
   " bash doesn't mind the parentheses.
   let cmd = '('

autoload/gitgutter/utility.vim

@@ -108,6 +108,7 @@ endfunction
 " * non-empty string - path
 " *               -1 - pending
 " *               -2 - not tracked by git
+" *               -3 - assume unchanged
 function! gitgutter#utility#repo_path(bufnr, shellesc) abort
   let p = gitgutter#utility#getbufvar(a:bufnr, 'path', '')
   return a:shellesc ? gitgutter#utility#shellescape(p) : p
@@ -116,9 +117,13 @@ endfunction
 
 let s:set_path_handler = {}
 
-function! s:set_path_handler.out(buffer, path) abort
-  let path = s:strip_trailing_new_line(a:path)
-  call gitgutter#utility#setbufvar(a:buffer, 'path', path)
+function! s:set_path_handler.out(buffer, listing) abort
+  let [status, path] = split(s:strip_trailing_new_line(a:listing))
+  if status =~ '[[:lower:]]'
+    call gitgutter#utility#setbufvar(a:buffer, 'path', -3)
+  else
+    call gitgutter#utility#setbufvar(a:buffer, 'path', path)
+  endif
 
   if type(self.continuation) == type(function('tr'))
     call self.continuation()
@@ -140,9 +145,10 @@ function! gitgutter#utility#set_repo_path(bufnr, continuation) abort
   " * non-empty string - path
   " *               -1 - pending
   " *               -2 - not tracked by git
+  " *               -3 - assume unchanged
 
   call gitgutter#utility#setbufvar(a:bufnr, 'path', -1)
-  let cmd = gitgutter#utility#cd_cmd(a:bufnr, g:gitgutter_git_executable.' '.g:gitgutter_git_args.' ls-files --error-unmatch --full-name -z -- '.gitgutter#utility#shellescape(s:filename(a:bufnr)))
+  let cmd = gitgutter#utility#cd_cmd(a:bufnr, g:gitgutter_git_executable.' '.g:gitgutter_git_args.' ls-files -v --error-unmatch --full-name -z -- '.gitgutter#utility#shellescape(s:filename(a:bufnr)))
 
   if g:gitgutter_async && gitgutter#async#available() && !has('vim_starting')
     let handler = copy(s:set_path_handler)
@@ -151,11 +157,18 @@ function! gitgutter#utility#set_repo_path(bufnr, continuation) abort
     return 'async'
   endif
 
-  let path = gitgutter#utility#system(cmd)
+  let listing = gitgutter#utility#system(cmd)
+
   if v:shell_error
     call gitgutter#utility#setbufvar(a:bufnr, 'path', -2)
+    return
+  endif
+
+  let [status, path] = split(s:strip_trailing_new_line(listing))
+  if status =~ '[[:lower:]]'
+    call gitgutter#utility#setbufvar(a:bufnr, 'path', -3)
   else
-    call gitgutter#utility#setbufvar(a:bufnr, 'path', s:strip_trailing_new_line(path))
+    call gitgutter#utility#setbufvar(a:bufnr, 'path', path)
   endif
 endfunction
 

test/test_gitgutter.vim

@@ -1126,3 +1126,12 @@ function Test_foldtext()
   call assert_equal(0, gitgutter#fold#is_changed())
   call assert_equal('+-  3 lines: a', gitgutter#fold#foldtext())
 endfunction
+
+
+function Test_assume_unchanged()
+  call system("git update-index --assume-unchanged fixture.txt")
+  unlet b:gitgutter.path  " it was already set when fixture.txt was loaded in SetUp()
+  normal ggo*
+  call s:trigger_gitgutter()
+  call s:assert_signs([], 'fixture.txt')
+endfunction