Add g:gitgutter_git_args for args to git when running git-diff.

See #541, #546.

README.mkd

@@ -212,6 +212,7 @@ You can customise:
 * The signs' colours and symbols
 * Line highlights
 * The base of the diff
+* Extra arguments for `git` when running `git diff`
 * Extra arguments for `git diff`
 * Key mappings
 * Whether or not vim-gitgutter is on initially (defaults to on)
@@ -297,6 +298,14 @@ let g:gitgutter_diff_base = '<commit SHA>'
 ```
 
 
+#### Extra arguments for `git` when running `git diff`
+
+If you want to pass extra arguments to `git` when running `git diff`, do so like this:
+
+```viml
+let g:gitgutter_git_args = '--git-dir-""'
+```
+
 #### Extra arguments for `git diff`
 
 If you want to pass extra arguments to `git diff`, for example to ignore whitespace, do so like this:

autoload/gitgutter/diff.vim

@@ -100,7 +100,7 @@ function! gitgutter#diff#run_diff(bufnr, preserve_full_diff) abort
   call s:write_buffer(a:bufnr, buff_file)
 
   " Call git-diff with the temporary files.
-  let cmd .= g:gitgutter_git_executable.' --no-pager'
+  let cmd .= g:gitgutter_git_executable.' --no-pager '.g:gitgutter_git_args
   if s:c_flag
     let cmd .= ' -c "diff.autorefreshindex=0"'
     let cmd .= ' -c "diff.noprefix=false"'

doc/gitgutter.txt

@@ -232,6 +232,7 @@ Most important option:~
 Git:~
 
     |g:gitgutter_git_executable|
+    |g:gitgutter_git_args|
     |g:gitgutter_diff_args|
     |g:gitgutter_diff_base|
 
@@ -270,6 +271,15 @@ Default: 'git'
 This option determines what git binary to use.  Set this if git is not on your
 path.
 
+                                                         *g:gitgutter_git_args*
+Default: empty
+
+Use this option to pass any extra arguments to git when running git-diff.
+For example:
+>
+    let g:gitgutter_git_args = '--git-dir=""'
+<
+
                                                         *g:gitgutter_diff_args*
 Default: empty
 

plugin/gitgutter.vim

@@ -45,6 +45,7 @@ else
 endif
 
 call s:set('g:gitgutter_sign_modified_removed',    '~_')
+call s:set('g:gitgutter_git_args',                   '')
 call s:set('g:gitgutter_diff_args',                  '')
 call s:set('g:gitgutter_diff_base',                  '')
 call s:set('g:gitgutter_map_keys',                    1)