Add hunk previewing.

README.mkd

@@ -7,7 +7,7 @@ Features:
 * Shows signs for added, modified, and removed lines.
 * Ensures signs are always as up to date as possible (but without running more than necessary).
 * Quick jumping between blocks of changed lines ("hunks").
-* Stage/revert individual hunks.
+* Stage/revert/preview individual hunks.
 * Optional line highlighting.
 * Fully customisable (signs, sign column, line highlights, mappings, extra git-diff arguments, etc).
 * Can be toggled on/off.
@@ -103,6 +103,12 @@ nmap <Leader>ha <Plug>GitGutterStageHunk
 nmap <Leader>hu <Plug>GitGutterRevertHunk
 ```
 
+And you can preview a hunk's changes with `<Leader>hp`.  You can of course change this mapping, e.g:
+
+```viml
+nmap <Leader>hv <Plug>GitGutterPreviewHunk
+```
+
 If you don't want vim-gitgutter to set up any mappings at all, use this:
 
 ```viml

autoload/diff.vim

@@ -178,13 +178,18 @@ function! diff#process_modified_and_removed(modifications, from_count, to_count,
   let a:modifications[-1] = [a:to_line + offset - 1, 'modified_removed']
 endfunction
 
-function! diff#generate_diff_for_hunk(hunk)
-  return diff#discard_hunks(diff#run_diff(0, 0), a:hunk)
+function! diff#generate_diff_for_hunk(hunk, keep_header)
+  let diff = diff#discard_hunks(diff#run_diff(0, 0), a:hunk, a:keep_header)
+  if !a:keep_header
+    " Discard summary line
+    let diff = join(split(diff, '\n')[1:-1], "\n")
+  endif
+  return diff
 endfunction
 
-function! diff#discard_hunks(diff, hunk_to_keep)
+function! diff#discard_hunks(diff, hunk_to_keep, keep_header)
   let modified_diff = []
-  let keep_line = 1  " start by keeping header
+  let keep_line = a:keep_header
   for line in split(a:diff, '\n')
     let hunk_info = diff#parse_hunk(line)
     if len(hunk_info) == 4  " start of new hunk

autoload/gitgutter.vim

@@ -119,7 +119,7 @@ function! gitgutter#stage_hunk()
     endif
 
     " construct a diff
-    let diff_for_hunk = diff#generate_diff_for_hunk(current_hunk)
+    let diff_for_hunk = diff#generate_diff_for_hunk(current_hunk, 1)
 
     " apply the diff
     call system(utility#command_in_directory_of_file('git apply --cached --unidiff-zero - '), diff_for_hunk)
@@ -142,7 +142,7 @@ function! gitgutter#revert_hunk()
     endif
 
     " construct a diff
-    let diff_for_hunk = diff#generate_diff_for_hunk(current_hunk)
+    let diff_for_hunk = diff#generate_diff_for_hunk(current_hunk, 1)
 
     " apply the diff
     call system(utility#command_in_directory_of_file('git apply --reverse --unidiff-zero - '), diff_for_hunk)
@@ -152,4 +152,32 @@ function! gitgutter#revert_hunk()
   endif
 endfunction
 
+function! gitgutter#preview_hunk()
+  if utility#is_active()
+    silent write
+
+    " find current hunk
+    let current_hunk = hunk#current_hunk()
+    if empty(current_hunk)
+      return
+    endif
+
+    " construct a diff
+    let diff_for_hunk = diff#generate_diff_for_hunk(current_hunk, 0)
+
+    " preview the diff
+    silent! wincmd P
+    if !&previewwindow
+      execute 'bo ' . &previewheight . ' new'
+      set previewwindow
+      setlocal filetype=diff buftype=nowrite
+    endif
+
+    execute "%delete_"
+    call append(0, split(diff_for_hunk, "\n"))
+
+    wincmd p
+  endif
+endfunction
+
 " }}}

doc/gitgutter.txt

@@ -105,6 +105,9 @@ Commands for staging or reverting individual hunks:
   :GitGutterRevertHunk                                   *:GitGutterRevertHunk*
       Revert the hunk the cursor is in.
 
+  :GitGutterPreviewHunk                                 *:GitGutterPreviewHunk*
+      Preview the hunk the cursor is in.
+
 ===============================================================================
 5. CUSTOMISATION                                       *GitGutterCustomisation*
 

plugin/gitgutter.vim

@@ -77,8 +77,9 @@ command GitGutterSignsToggle  call gitgutter#signs_toggle()
 command -count=1 GitGutterNextHunk call hunk#next_hunk(<count>)
 command -count=1 GitGutterPrevHunk call hunk#prev_hunk(<count>)
 
-command GitGutterStageHunk  call gitgutter#stage_hunk()
-command GitGutterRevertHunk call gitgutter#revert_hunk()
+command GitGutterStageHunk   call gitgutter#stage_hunk()
+command GitGutterRevertHunk  call gitgutter#revert_hunk()
+command GitGutterPreviewHunk call gitgutter#preview_hunk()
 
 " Returns the git-diff hunks for the file or an empty list if there
 " aren't any hunks.
@@ -127,8 +128,9 @@ if g:gitgutter_map_keys
 endif
 
 
-nnoremap <silent> <Plug>GitGutterStageHunk :GitGutterStageHunk<CR>
-nnoremap <silent> <Plug>GitGutterRevertHunk :GitGutterRevertHunk<CR>
+nnoremap <silent> <Plug>GitGutterStageHunk   :GitGutterStageHunk<CR>
+nnoremap <silent> <Plug>GitGutterRevertHunk  :GitGutterRevertHunk<CR>
+nnoremap <silent> <Plug>GitGutterPreviewHunk :GitGutterPreviewHunk<CR>
 
 if g:gitgutter_map_keys
   if !hasmapto('<Plug>GitGutterStageHunk') && maparg('<Leader>hs', 'n') ==# ''
@@ -137,6 +139,9 @@ if g:gitgutter_map_keys
   if !hasmapto('<Plug>GitGutterRevertHunk') && maparg('<Leader>hr', 'n') ==# ''
     nmap <Leader>hr <Plug>GitGutterRevertHunk
   endif
+  if !hasmapto('<Plug>GitGutterPreviewHunk') && maparg('<Leader>hp', 'n') ==# ''
+    nmap <Leader>hp <Plug>GitGutterPreviewHunk
+  endif
 endif
 
 " }}}