Fix staging of hunks coming after deleted lines.

Previously vim-gitgutter generated context-free patches and applied
those to the index.  However when staging a hunk situated after any
deleted lines, the line numbers on the patch were out by the number
of lines deleted, and without any context git would apply the patch
to the wrong part of the file in the index.

This commit ensure patches are generated with 1 line of context,
allowing git to adjust the line numbers appropriately and apply the
patch to the right location.

More lines of context would help git more to adjust line numbers; but
the more context we have the more we group together hunks we would
like to treat separately.

autoload/gitgutter.vim

@@ -19,7 +19,7 @@ function! gitgutter#process_buffer(file, realtime)
     endif
     try
       if !a:realtime || gitgutter#utility#has_fresh_changes(a:file)
-        let diff = gitgutter#diff#run_diff(a:realtime || gitgutter#utility#has_unsaved_changes(a:file), 1)
+        let diff = gitgutter#diff#run_diff(a:realtime || gitgutter#utility#has_unsaved_changes(a:file), 1, 0)
         call gitgutter#hunk#set_hunks(gitgutter#diff#parse_diff(diff))
         let modified_lines = gitgutter#diff#process_hunks(gitgutter#hunk#hunks())
 
@@ -156,17 +156,11 @@ function! gitgutter#stage_hunk()
     " It doesn't make sense to stage a hunk otherwise.
     silent write
 
-    " find current hunk
-    let current_hunk = gitgutter#hunk#current_hunk()
-    if empty(current_hunk)
-      return
-    endif
-
     " construct a diff
-    let diff_for_hunk = gitgutter#diff#generate_diff_for_hunk(current_hunk, 1)
+    let diff_for_hunk = gitgutter#diff#generate_diff_for_hunk(1, 1)
 
     " apply the diff
-    call gitgutter#utility#system(gitgutter#utility#command_in_directory_of_file('git apply --cached --unidiff-zero - '), diff_for_hunk)
+    call gitgutter#utility#system(gitgutter#utility#command_in_directory_of_file('git apply --cached --recount --allow-overlap - '), diff_for_hunk)
 
     " refresh gitgutter's view of buffer
     silent execute "GitGutter"
@@ -179,17 +173,11 @@ function! gitgutter#revert_hunk()
     " It doesn't make sense to stage a hunk otherwise.
     silent write
 
-    " find current hunk
-    let current_hunk = gitgutter#hunk#current_hunk()
-    if empty(current_hunk)
-      return
-    endif
-
     " construct a diff
-    let diff_for_hunk = gitgutter#diff#generate_diff_for_hunk(current_hunk, 1)
+    let diff_for_hunk = gitgutter#diff#generate_diff_for_hunk(1, 1)
 
     " apply the diff
-    call gitgutter#utility#system(gitgutter#utility#command_in_directory_of_file('git apply --reverse --unidiff-zero - '), diff_for_hunk)
+    call gitgutter#utility#system(gitgutter#utility#command_in_directory_of_file('git apply --reverse - '), diff_for_hunk)
 
     " reload file
     silent edit
@@ -200,14 +188,8 @@ function! gitgutter#preview_hunk()
   if gitgutter#utility#is_active()
     silent write
 
-    " find current hunk
-    let current_hunk = gitgutter#hunk#current_hunk()
-    if empty(current_hunk)
-      return
-    endif
-
     " construct a diff
-    let diff_for_hunk = gitgutter#diff#generate_diff_for_hunk(current_hunk, 0)
+    let diff_for_hunk = gitgutter#diff#generate_diff_for_hunk(0, 0)
 
     " preview the diff
     silent! wincmd P

autoload/gitgutter/diff.vim

@@ -3,7 +3,7 @@ let s:grep_command = ' | ' . (g:gitgutter_escape_grep ? '\grep' : 'grep') . ' -e
 let s:hunk_re = '^@@ -\(\d\+\),\?\(\d*\) +\(\d\+\),\?\(\d*\) @@'
 
 
-function! gitgutter#diff#run_diff(realtime, use_external_grep)
+function! gitgutter#diff#run_diff(realtime, use_external_grep, lines_of_context)
   " Wrap compound command in parentheses to make Windows happy.
   let cmd = '(git ls-files --error-unmatch ' . gitgutter#utility#shellescape(gitgutter#utility#filename()) . ' && ('
 
@@ -11,9 +11,9 @@ function! gitgutter#diff#run_diff(realtime, use_external_grep)
     let blob_name = ':' . gitgutter#utility#shellescape(gitgutter#utility#file_relative_to_repo_root())
     let blob_file = tempname()
     let cmd .= 'git show ' . blob_name . ' > ' . blob_file .
-          \ ' && diff -U0 ' . g:gitgutter_diff_args . ' ' . blob_file . ' - '
+          \ ' && diff -U'.a:lines_of_context.' ' . g:gitgutter_diff_args . ' ' . blob_file . ' - '
   else
-    let cmd .= 'git diff --no-ext-diff --no-color -U0 ' . g:gitgutter_diff_args . ' ' . gitgutter#utility#shellescape(gitgutter#utility#filename())
+    let cmd .= 'git diff --no-ext-diff --no-color -U'.a:lines_of_context.' ' . g:gitgutter_diff_args . ' ' . gitgutter#utility#shellescape(gitgutter#utility#filename())
   endif
 
   if a:use_external_grep && s:grep_available
@@ -182,22 +182,24 @@ function! gitgutter#diff#process_modified_and_removed(modifications, from_count,
   let a:modifications[-1] = [a:to_line + offset - 1, 'modified_removed']
 endfunction
 
-function! gitgutter#diff#generate_diff_for_hunk(hunk, keep_header)
-  let diff = gitgutter#diff#discard_hunks(gitgutter#diff#run_diff(0, 0), a:hunk, a:keep_header)
+function! gitgutter#diff#generate_diff_for_hunk(keep_header, lines_of_context)
+  let diff = gitgutter#diff#run_diff(0, 0, a:lines_of_context)
+  let diff_for_hunk = gitgutter#diff#discard_hunks(diff, a:keep_header)
   if !a:keep_header
     " Discard summary line
-    let diff = join(split(diff, '\n')[1:-1], "\n")
+    let diff_for_hunk = join(split(diff_for_hunk, '\n')[1:-1], "\n")
   endif
-  return diff
+  return diff_for_hunk
 endfunction
 
-function! gitgutter#diff#discard_hunks(diff, hunk_to_keep, keep_header)
+" diff - with non-zero lines of context
+function! gitgutter#diff#discard_hunks(diff, keep_header)
   let modified_diff = []
   let keep_line = a:keep_header
   for line in split(a:diff, '\n')
     let hunk_info = gitgutter#diff#parse_hunk(line)
     if len(hunk_info) == 4  " start of new hunk
-      let keep_line = (hunk_info == a:hunk_to_keep)
+      let keep_line = gitgutter#hunk#cursor_in_hunk(hunk_info)
     endif
     if keep_line
       call add(modified_diff, line)

autoload/gitgutter/hunk.vim

@@ -67,15 +67,9 @@ endfunction
 " hunk.
 function! gitgutter#hunk#current_hunk()
   let current_hunk = []
-  let current_line = line('.')
 
   for hunk in s:hunks
-    if current_line == 1 && hunk[2] == 0
-      let current_hunk = hunk
-      break
-    endif
-
-    if current_line >= hunk[2] && current_line < hunk[2] + (hunk[3] == 0 ? 1 : hunk[3])
+    if gitgutter#hunk#cursor_in_hunk(hunk)
       let current_hunk = hunk
       break
     endif
@@ -86,3 +80,17 @@ function! gitgutter#hunk#current_hunk()
   endif
 endfunction
 
+function! gitgutter#hunk#cursor_in_hunk(hunk)
+  let current_line = line('.')
+
+  if current_line == 1 && a:hunk[2] == 0
+    return 1
+  endif
+
+  if current_line >= a:hunk[2] && current_line < a:hunk[2] + (a:hunk[3] == 0 ? 1 : a:hunk[3])
+    return 1
+  endif
+
+  return 0
+endfunction
+