Add g:gitgutter_sign_allow_clobber to control clobbering.

I.e. how gitgutter handles non-gitgutter signs.

See #565, #627.

Co-authored-by: Andy Stewart <boss@airbladesoftware.com>

README.mkd

@@ -242,6 +242,7 @@ You can customise:
 
 * The sign column's colours
 * Whether or not the sign column is shown when there aren't any signs (defaults to no)
+* How to handle non-gitgutter signs
 * The signs' colours and symbols
 * Line highlights
 * The base of the diff
@@ -286,6 +287,12 @@ else
 endif
 ```
 
+GitGutter will preserve non-gitgutter signs by default.  If you don't want gitgutter to worry about this (e.g. if you use a NeoVim with an expanding sign column):
+
+```viml
+let g:gitgutter_sign_allow_clobber = 1
+```
+
 
 #### Signs' colours and symbols
 

autoload/gitgutter/sign.vim

@@ -96,7 +96,9 @@ endfunction
 
 function! s:find_current_signs(bufnr) abort
   let gitgutter_signs = {}  " <line_number (string)>: {'id': <id (number)>, 'name': <name (string)>}
+  if !g:gitgutter_sign_allow_clobber
     let other_signs = []      " [<line_number (number),...]
+  endif
   let dummy_sign_placed = 0
 
   redir => signs
@@ -122,14 +124,18 @@ function! s:find_current_signs(bufnr) abort
         endif
         let gitgutter_signs[line_number] = {'id': id, 'name': name}
       else
+        if !g:gitgutter_sign_allow_clobber
           call add(other_signs, line_number)
         endif
+      endif
     end
   endfor
 
   call gitgutter#utility#setbufvar(a:bufnr, 'dummy_sign', dummy_sign_placed)
   call gitgutter#utility#setbufvar(a:bufnr, 'gitgutter_signs', gitgutter_signs)
+  if !g:gitgutter_sign_allow_clobber
     call gitgutter#utility#setbufvar(a:bufnr, 'other_signs', other_signs)
+  endif
 endfunction
 
 
@@ -152,7 +158,7 @@ endfunction
 
 
 function! s:remove_signs(bufnr, sign_ids, all_signs) abort
-  if a:all_signs && s:supports_star && empty(gitgutter#utility#getbufvar(a:bufnr, 'other_signs'))
+  if a:all_signs && s:supports_star && (g:gitgutter_sign_allow_clobber || empty(gitgutter#utility#getbufvar(a:bufnr, 'other_signs')))
     let dummy_sign_present = gitgutter#utility#getbufvar(a:bufnr, 'dummy_sign')
     execute "sign unplace * buffer=" . a:bufnr
     if dummy_sign_present
@@ -167,7 +173,9 @@ endfunction
 
 
 function! s:upsert_new_gitgutter_signs(bufnr, modified_lines) abort
+  if !g:gitgutter_sign_allow_clobber
     let other_signs = gitgutter#utility#getbufvar(a:bufnr, 'other_signs')
+  endif
   let old_gitgutter_signs = gitgutter#utility#getbufvar(a:bufnr, 'gitgutter_signs')
 
   " Handle special case where the first line is the site of two hunks:
@@ -181,7 +189,7 @@ function! s:upsert_new_gitgutter_signs(bufnr, modified_lines) abort
 
   for line in modified_lines
     let line_number = line[0]  " <number>
-    if index(other_signs, line_number) == -1  " don't clobber others' signs
+    if g:gitgutter_sign_allow_clobber || index(other_signs, line_number) == -1  " don't clobber others' signs
       let name = s:highlight_name_for_change(line[1])
       if !has_key(old_gitgutter_signs, line_number)  " insert
         let id = s:next_sign_id()

doc/gitgutter.txt

@@ -376,6 +376,12 @@ signs, so to avoid slowing down the GUI the number of signs is capped.  When
 the number of changed lines exceeds this value, the plugin removes all signs
 and displays a warning message.
 
+                                               *g:gitgutter_sign_allow_clobber*
+Default: 0
+
+Determines whether gitgutter preserves non-gitgutter signs (the default). When
+1, gitgutter will not preserve non-gitgutter signs.
+
                                           *g:gitgutter_sign_added*
                                           *g:gitgutter_sign_modified*
                                           *g:gitgutter_sign_removed*

plugin/gitgutter.vim

@@ -28,6 +28,7 @@ call s:set('g:gitgutter_max_signs',                 500)
 call s:set('g:gitgutter_signs',                       1)
 call s:set('g:gitgutter_highlight_lines',             0)
 call s:set('g:gitgutter_highlight_linenrs',           0)
+call s:set('g:gitgutter_sign_allow_clobber',          0)
 call s:set('g:gitgutter_sign_column_always',          0)
 if g:gitgutter_sign_column_always && exists('&signcolumn')
   " Vim 7.4.2201.