Allow configuration of floating window appearance

Closes #807.

README.mkd

@@ -299,6 +299,7 @@ You can customise:
 * Whether to clobber or preserve non-gitgutter signs
 * The priority of gitgutter's signs.
 * Whether to use a floating/popup window for hunk previews
+* The appearance of a floating/popup window for hunk previews
 * Whether to populate the quickfix list or a location list with all hunks
 
 Please note that vim-gitgutter won't override any colours or highlights you've set in your colorscheme.
@@ -519,6 +520,11 @@ let g:gitgutter_async = 0
 Add `let g:gitgutter_preview_win_floating = 1` to your `~/.vimrc`.  Note that on Vim this prevents you staging (partial) hunks via the preview window.
 
 
+#### The appearance of a floating/popup window for hunk previews
+
+Set `g:gitgutter_floating_window_options` to a dictionary of the options you want.  This dictionary is passed directly to `popup_create()` (Vim) / `nvim_open_win()` (Neovim).
+
+
 #### To load all hunks into the current window's location list instead of the quickfix list
 
 Add `let g:gitgutter_use_location_list = 1` to your `~/.vimrc`.

autoload/gitgutter/hunk.vim

@@ -431,14 +431,7 @@ function! s:open_hunk_preview_window()
 
       let buf = nvim_create_buf(v:false, v:false)
       " Set default width and height for now.
-      let s:winid = nvim_open_win(buf, v:false, {
+      let s:winid = nvim_open_win(buf, v:false, g:gitgutter_floating_window_options)
-            \ 'relative': 'cursor',
-            \ 'row': 1,
-            \ 'col': 0,
-            \ 'width': 42,
-            \ 'height': &previewheight,
-            \ 'style': 'minimal'
-            \ })
       call nvim_buf_set_option(buf, 'filetype',  'diff')
       call nvim_buf_set_option(buf, 'buftype',   'acwrite')
       call nvim_buf_set_option(buf, 'bufhidden', 'delete')
@@ -461,16 +454,11 @@ function! s:open_hunk_preview_window()
     endif
 
     if exists('*popup_create')
-      let opts = {
-            \ 'line': 'cursor+1',
-            \ 'col': 'cursor',
-            \ 'moved': 'any',
-            \ }
       if g:gitgutter_close_preview_on_escape
-        let opts.filter = function('s:close_popup_on_escape')
+        let g:gitgutter_floating_window_options.filter = function('s:close_popup_on_escape')
       endif
 
-      let s:winid = popup_create('', opts)
+      let s:winid = popup_create('', g:gitgutter_floating_window_options)
 
       call setbufvar(winbufnr(s:winid), '&filetype', 'diff')
 
@@ -515,7 +503,7 @@ function! s:populate_hunk_preview_window(header, body)
 
   if g:gitgutter_preview_win_floating
     if exists('*nvim_open_win')
-      let height = min([body_length, &previewheight])
+      let height = min([body_length, g:gitgutter_floating_window_options.height])
 
       " Assumes cursor is not in previewing window.
       call nvim_buf_set_var(winbufnr(s:winid), 'hunk_header', a:header)

doc/gitgutter.txt

@@ -348,6 +348,7 @@ Hunk jumping:~
 Hunk previews:~
 
     |g:gitgutter_preview_win_floating|
+    |g:gitgutter_floating_window_options|
     |g:gitgutter_close_preview_on_escape|
 
 Terminal:~
@@ -508,6 +509,29 @@ Whether to use floating/popup windows for hunk previews.  Note that if you use
 popup windows on Vim you will not be able to stage partial hunks via the
 preview window.
 
+                                          *g:gitgutter_floating_window_options*
+Default:
+>
+    " Vim
+    {
+        \ 'line': 'cursor+1',
+        \ 'col': 'cursor',
+        \ 'moved': 'any'
+    }
+
+    " Neovim
+    {
+        \ 'relative': 'cursor',
+        \ 'row': 1,
+        \ 'col': 0,
+        \ 'width': 42,
+        \ 'height': &previewheight,
+        \ 'style': 'minimal'
+    }
+<
+This dictionary is passed directly to |popup_create()| (Vim) or
+|nvim_open_win()| (Neovim).
+
                                           *g:gitgutter_close_preview_on_escape*
 Default: 0
 

plugin/gitgutter.vim

@@ -24,9 +24,22 @@ endfunction
 let g:gitgutter_preview_win_location = get(g:, 'gitgutter_preview_win_location', 'bo')
 if exists('*nvim_open_win')
   let g:gitgutter_preview_win_floating = get(g:, 'gitgutter_preview_win_floating', 1)
+  let g:gitgutter_floating_window_options = get(g:, 'gitgutter_floating_window_options', {
+        \ 'relative': 'cursor',
+        \ 'row': 1,
+        \ 'col': 0,
+        \ 'width': 42,
+        \ 'height': &previewheight,
+        \ 'style': 'minimal'
+        \ })
 else
   let default = exists('&previewpopup') ? !empty(&previewpopup) : 0
   let g:gitgutter_preview_win_floating = get(g:, 'gitgutter_preview_win_floating', default)
+  let g:gitgutter_floating_window_options = get(g:, 'gitgutter_floating_window_options', {
+        \ 'line': 'cursor+1',
+        \ 'col': 'cursor',
+        \ 'moved': 'any'
+        \ })
 endif
 let g:gitgutter_enabled = get(g:, 'gitgutter_enabled', 1)
 if exists('*sign_unplace')