From acdd74bc6cc88afffe2586e2b8ec8e7746d9acc9 Mon Sep 17 00:00:00 2001
From: Lewis Russell <lewis6991@gmail.com>
Date: Fri, 1 Apr 2022 12:26:19 +0100
Subject: [PATCH] feat(diffthis): various improvements

- When running diffthis (or vim-fugitive's Gdiffsplit), hunk operations
  to the index will now update the diff buffer.

- Similar to vim-fugitive's Gdiffsplit, buffers of a file in the git
  index can now be edited. When the buffer is written, it updates the
  git index accordingly. Likewise the index buffer can also be reloaded
  (via 'edit').

- Moved all diffthis code to a separate module.

Fixes #501
---
 doc/gitsigns.txt             |   3 +
 gitsigns.nvim-scm-1.rockspec |   1 +
 lua/gitsigns/actions.lua     | 100 ++++-----------------
 lua/gitsigns/async.lua       |   2 +
 lua/gitsigns/cache.lua       |  10 +++
 lua/gitsigns/debounce.lua    |   6 +-
 lua/gitsigns/diffthis.lua    | 162 +++++++++++++++++++++++++++++++++++
 lua/gitsigns/git.lua         |  15 +++-
 lua/gitsigns/manager.lua     |   2 +-
 lua/gitsigns/util.lua        |  24 ++++++
 teal/gitsigns/actions.tl     | 108 +++++------------------
 teal/gitsigns/async.tl       |   2 +
 teal/gitsigns/cache.tl       |  10 +++
 teal/gitsigns/debounce.tl    |   6 +-
 teal/gitsigns/diffthis.tl    | 162 +++++++++++++++++++++++++++++++++++
 teal/gitsigns/git.tl         |  15 +++-
 teal/gitsigns/manager.tl     |   2 +-
 teal/gitsigns/util.tl        |  24 ++++++
 types/types.d.tl             |  23 ++++-
 19 files changed, 499 insertions(+), 178 deletions(-)
 create mode 100644 lua/gitsigns/diffthis.lua
 create mode 100644 teal/gitsigns/diffthis.tl

diff --git a/doc/gitsigns.txt b/doc/gitsigns.txt
index 5346567..7cfbdbc 100644
--- a/doc/gitsigns.txt
+++ b/doc/gitsigns.txt
@@ -182,6 +182,9 @@ diffthis({base})                                         *gitsigns.diffthis()*
                 Perform a |vimdiff| on the given file with {base} if it is
                 given, or with the currently set base (index by default).
 
+                If {base} is the index, then the opened diff buffer is editable
+                and any written changes will update the index accordingly.
+
                 Examples: >
                   " Diff against the index
                   :Gitsigns diffthis
diff --git a/gitsigns.nvim-scm-1.rockspec b/gitsigns.nvim-scm-1.rockspec
index 07afca4..fd0f3e5 100644
--- a/gitsigns.nvim-scm-1.rockspec
+++ b/gitsigns.nvim-scm-1.rockspec
@@ -40,6 +40,7 @@ build = {
     ['gitsigns.current_line_blame']    = 'lua/gitsigns/current_line_blame.lua',
     ['gitsigns.debounce']              = 'lua/gitsigns/debounce.lua',
     ['gitsigns.debug']                 = 'lua/gitsigns/debug.lua',
+    ['gitsigns.diffthis']              = 'lua/gitsigns/diffthis.lua',
     ['gitsigns.diff_ext']              = 'lua/gitsigns/diff_ext.lua',
     ['gitsigns.diff_int']              = 'lua/gitsigns/diff_int.lua',
     ['gitsigns.diff_int.xdl_diff_ffi'] = 'lua/gitsigns/diff_int/xdl_diff_ffi.lua',
diff --git a/lua/gitsigns/actions.lua b/lua/gitsigns/actions.lua
index e9ecdd1..2f44e26 100644
--- a/lua/gitsigns/actions.lua
+++ b/lua/gitsigns/actions.lua
@@ -115,6 +115,13 @@ local function get_cursor_hunk(bufnr, hunks)
    return gs_hunks.find_hunk(lnum, hunks)
 end
 
+local function update(bufnr)
+   manager.update(bufnr)
+   if vim.wo.diff then
+      require('gitsigns.diffthis').update(bufnr)
+   end
+end
+
 
 
 
@@ -165,7 +172,7 @@ M.stage_hunk = mk_repeatable(void(function(range)
    table.insert(bcache.staged_diffs, hunk)
 
    bcache.compare_text = nil
-   manager.update(bufnr)
+   update(bufnr)
 end))
 
 
@@ -249,7 +256,7 @@ M.undo_stage_hunk = void(function()
 
    bcache.git_obj:stage_hunks({ hunk }, true)
    bcache.compare_text = nil
-   manager.update(bufnr)
+   update(bufnr)
 end)
 
 
@@ -283,7 +290,7 @@ M.stage_buffer = void(function()
    end
    bcache.compare_text = nil
 
-   manager.update(bufnr)
+   update(bufnr)
 end)
 
 
@@ -311,7 +318,7 @@ M.reset_buffer_index = void(function()
    bcache.compare_text = nil
 
    scheduler()
-   manager.update(bufnr)
+   update(bufnr)
 end)
 
 local function process_nav_opts(opts)
@@ -452,22 +459,6 @@ local function noautocmd(f)
 end
 
 
-local function strip_cr(xs0)
-   for i = 1, #xs0 do
-      if xs0[i]:sub(-1) ~= '\r' then
-
-         return xs0
-      end
-   end
-
-   local xs = vim.deepcopy(xs0)
-   for i = 1, #xs do
-      xs[i] = xs[i]:sub(1, -2)
-   end
-   return xs
-end
-
-
 
 M.preview_hunk = noautocmd(function()
 
@@ -479,7 +470,7 @@ M.preview_hunk = noautocmd(function()
 
    local hlines = gs_hunks.patch_lines(hunk)
    if vim.bo[cbuf].fileformat == 'dos' then
-      hlines = strip_cr(hlines)
+      hlines = util.strip_cr(hlines)
    end
 
    local lines = {
@@ -677,17 +668,10 @@ M.blame_line = void(function(opts)
    end
 end)
 
-local function calc_base(base)
-   if base and base:sub(1, 1):match('[~\\^]') then
-      base = 'HEAD' .. base
-   end
-   return base
-end
-
 local function update_buf_base(buf, bcache, base)
    bcache.base = base
    bcache.compare_text = nil
-   manager.update(buf, bcache)
+   update(buf)
 end
 
 
@@ -724,7 +708,7 @@ end
 
 
 M.change_base = void(function(base, global)
-   base = calc_base(base)
+   base = util.calc_base(base)
 
    if global then
       config.base = base
@@ -765,61 +749,13 @@ end
 
 
 
-M.diffthis = void(function(base)
-   local bufnr = current_buf()
-   local bcache = cache[bufnr]
-   if not bcache then return end
-
-   if api.nvim_win_get_option(0, 'diff') then return end
-
-   local ff = vim.bo[bufnr].fileformat
-
-   local text
-   local err
-   local comp_rev = bcache:get_compare_rev(calc_base(base))
-
-   if base then
-      text, err = bcache.git_obj:get_show_text(comp_rev)
-      if ff == 'dos' then
-         text = strip_cr(text)
-      end
-      if err then
-         print(err)
-         return
-      end
-      scheduler()
-   else
-      text = bcache:get_compare_text()
-   end
-
-   local ft = api.nvim_buf_get_option(bufnr, 'filetype')
-
-   local bufname = string.format(
-   'gitsigns://%s/%s',
-   bcache.git_obj.repo.gitdir,
-   comp_rev .. ':' .. bcache.git_obj.relpath)
 
 
-   vim.cmd('diffthis')
 
-   vim.cmd(table.concat({
-      'keepalt', 'aboveleft',
-      config.diff_opts.vertical and 'vertical' or '',
-      'split', bufname,
-   }, ' '))
-
-   local dbuf = current_buf()
-
-   api.nvim_buf_set_option(dbuf, 'modifiable', true)
-   util.set_lines(dbuf, 0, -1, text)
-   api.nvim_buf_set_option(dbuf, 'modifiable', false)
-
-   api.nvim_buf_set_option(dbuf, 'filetype', ft)
-   api.nvim_buf_set_option(dbuf, 'buftype', 'nowrite')
-   api.nvim_buf_set_option(dbuf, 'bufhidden', 'wipe')
-
-   vim.cmd('diffthis')
-end)
+M.diffthis = function(base)
+   local diffthis = require('gitsigns.diffthis')
+   diffthis.run(base, config.diff_opts.vertical)
+end
 
 local function hunks_to_qflist(buf_or_filename, hunks, qflist)
    for i, hunk in ipairs(hunks) do
diff --git a/lua/gitsigns/async.lua b/lua/gitsigns/async.lua
index 7acd7be..574aca5 100644
--- a/lua/gitsigns/async.lua
+++ b/lua/gitsigns/async.lua
@@ -5,6 +5,7 @@ local fun1 = {}
 local fun2 = {}
 local fun2_2 = {}
 local fun3 = {}
+local fun4 = {}
 
 local Async = {}
 
@@ -18,6 +19,7 @@ local Async = {}
 
 
 
+
 local async_thread = {
    threads = {},
 }
diff --git a/lua/gitsigns/cache.lua b/lua/gitsigns/cache.lua
index 43aab9d..9838afd 100644
--- a/lua/gitsigns/cache.lua
+++ b/lua/gitsigns/cache.lua
@@ -29,6 +29,7 @@ local M = {CacheEntry = {}, CacheObj = {}, }
 
 
 
+
 
 
 local CacheEntry = M.CacheEntry
@@ -48,6 +49,15 @@ CacheEntry.get_compare_rev = function(self, base)
    return string.format(':%d', stage)
 end
 
+CacheEntry.get_diffthis_bufname = function(self, rev)
+   rev = rev or self:get_compare_rev()
+   return string.format(
+   'gitsigns://%s/%s',
+   self.git_obj.repo.gitdir,
+   rev .. ':' .. self.git_obj.relpath)
+
+end
+
 CacheEntry.get_compare_text = function(self)
    if self.compare_text then
       return self.compare_text
diff --git a/lua/gitsigns/debounce.lua b/lua/gitsigns/debounce.lua
index 9363433..1da1008 100644
--- a/lua/gitsigns/debounce.lua
+++ b/lua/gitsigns/debounce.lua
@@ -51,7 +51,7 @@ end
 
 
 
-function M.throttle_by_id(fn)
+function M.throttle_by_id(fn, schedule)
    local scheduled = {}
    local running = {}
    return function(id, ...)
@@ -59,7 +59,9 @@ function M.throttle_by_id(fn)
 
          return
       end
-      scheduled[id] = true
+      if not running[id] or schedule then
+         scheduled[id] = true
+      end
       if running[id] then
          return
       end
diff --git a/lua/gitsigns/diffthis.lua b/lua/gitsigns/diffthis.lua
new file mode 100644
index 0000000..8957aa7
--- /dev/null
+++ b/lua/gitsigns/diffthis.lua
@@ -0,0 +1,162 @@
+local api = vim.api
+
+local void = require('gitsigns.async').void
+local scheduler = require('gitsigns.async').scheduler
+local awrap = require('gitsigns.async').wrap
+
+local gs_cache = require('gitsigns.cache')
+local cache = gs_cache.cache
+local CacheEntry = gs_cache.CacheEntry
+
+local nvim = require('gitsigns.nvim')
+local util = require('gitsigns.util')
+local manager = require('gitsigns.manager')
+
+local throttle_by_id = require('gitsigns.debounce').throttle_by_id
+
+local input = awrap(vim.ui.input, 2)
+
+local M = {}
+
+
+
+
+local bufread = void(function(bufnr, dbufnr, base, bcache)
+   local comp_rev = bcache:get_compare_rev(util.calc_base(base))
+   local text
+   if util.calc_base(base) == util.calc_base(bcache.base) then
+      text = bcache:get_compare_text()
+   else
+      local err
+      text, err = bcache.git_obj:get_show_text(comp_rev)
+      if err then
+         print(err)
+         return
+      end
+      if vim.bo[bufnr].fileformat == 'dos' then
+         text = util.strip_cr(text)
+      end
+      scheduler()
+   end
+
+   local modifiable = vim.bo[dbufnr].modifiable
+   vim.bo[dbufnr].modifiable = true
+   util.set_lines(dbufnr, 0, -1, text)
+
+   vim.bo[dbufnr].modifiable = modifiable
+   vim.bo[dbufnr].modified = false
+   vim.bo[dbufnr].filetype = vim.bo[bufnr].filetype
+   vim.bo[dbufnr].bufhidden = 'wipe'
+
+   vim.cmd('diffthis')
+end)
+
+local bufwrite = void(function(bufnr, dbufnr, base, bcache)
+   local buftext = util.buf_lines(dbufnr)
+   bcache.git_obj:stage_lines(buftext)
+   vim.bo[dbufnr].modified = false
+
+
+   if util.calc_base(base) == util.calc_base(bcache.base) then
+      bcache.compare_text = buftext
+      manager.update(bufnr, bcache)
+   end
+end)
+
+M.run = void(function(base, vertical)
+   local bufnr = vim.api.nvim_get_current_buf()
+   local bcache = cache[bufnr]
+   if not bcache then
+      return
+   end
+
+   if vim.wo.diff then
+      return
+   end
+
+   local comp_rev = bcache:get_compare_rev(util.calc_base(base))
+   local bufname = bcache:get_diffthis_bufname(comp_rev)
+
+   vim.cmd('diffthis')
+
+   vim.cmd(table.concat({
+      'keepalt', 'aboveleft',
+      vertical and 'vertical' or '',
+      'split', bufname,
+   }, ' '))
+
+   local dbuf = vim.api.nvim_get_current_buf()
+
+   bufread(bufnr, dbuf, base, bcache)
+
+   if comp_rev == ':0' then
+      vim.bo[dbuf].buftype = 'acwrite'
+
+      nvim.autocmd('BufReadCmd', {
+         group = 'gitsigns',
+         buffer = dbuf,
+         callback = function()
+            bufread(bufnr, dbuf, base, bcache)
+         end,
+      })
+
+      nvim.autocmd('BufWriteCmd', {
+         group = 'gitsigns',
+         buffer = dbuf,
+         callback = function()
+            bufwrite(bufnr, dbuf, base, bcache)
+         end,
+      })
+   else
+      vim.bo[dbuf].buftype = 'nowrite'
+      vim.bo[dbuf].modifiable = false
+   end
+end)
+
+
+local function should_reload(bufnr)
+   if not vim.bo[bufnr].modified then
+      return true
+   end
+   local response
+   while not vim.tbl_contains({ 'O', 'L' }, response) do
+      response = input({
+         prompt = 'Warning: The git index has changed and the buffer was changed as well. [O]K, (L)oad File:',
+      })
+   end
+   return response == 'L'
+end
+
+
+M.update = throttle_by_id(void(function(bufnr)
+   if not vim.wo.diff then
+      return
+   end
+
+   local bcache = cache[bufnr]
+
+
+
+   local bufname = bcache:get_diffthis_bufname()
+
+   for _, w in ipairs(api.nvim_list_wins()) do
+      if api.nvim_win_is_valid(w) then
+         local b = api.nvim_win_get_buf(w)
+         local bname = api.nvim_buf_get_name(b)
+         if bname == bufname or vim.startswith(bname, 'fugitive://') then
+            if should_reload(b) then
+               api.nvim_buf_call(b, function()
+
+
+
+
+                  vim.cmd('doautocmd BufReadCmd')
+                  vim.cmd('diffthis')
+               end)
+            end
+         end
+      end
+   end
+end))
+
+return M
diff --git a/lua/gitsigns/git.lua b/lua/gitsigns/git.lua
index ecd1f70..52f1569 100644
--- a/lua/gitsigns/git.lua
+++ b/lua/gitsigns/git.lua
@@ -107,6 +107,7 @@ local M = {BlameInfo = {}, Version = {}, Repo = {}, FileProps = {}, Obj = {}, }
 
 
 
+
 
 
 local in_git_dir = function(file)
@@ -451,7 +452,7 @@ Obj.ensure_file_in_index = function(self)
       else
 
 
-         local info = table.concat({ self.mode_bits, self.object_name, self.relpath }, ',')
+         local info = string.format('%s,%s,%s', self.mode_bits, self.object_name, self.relpath)
          self:command({ 'update-index', '--add', '--cacheinfo', info })
       end
 
@@ -459,6 +460,18 @@ Obj.ensure_file_in_index = function(self)
    end
 end
 
+Obj.stage_lines = function(self, lines)
+   local stdout = self:command({
+      'hash-object', '-w', '--path', self.relpath, '--stdin',
+   }, { writer = lines })
+
+   local new_object = stdout[1]
+
+   self:command({
+      'update-index', '--cacheinfo', string.format('%s,%s,%s', self.mode_bits, new_object, self.relpath),
+   })
+end
+
 Obj.stage_hunks = function(self, hunks, invert)
    self:ensure_file_in_index()
    self:command({
diff --git a/lua/gitsigns/manager.lua b/lua/gitsigns/manager.lua
index 28a5e02..a1ba03f 100644
--- a/lua/gitsigns/manager.lua
+++ b/lua/gitsigns/manager.lua
@@ -328,7 +328,7 @@ end
 
 
 
-M.update = throttle_by_id(update0)
+M.update = throttle_by_id(update0, true)
 
 M.setup = function()
    M.update_debounced = debounce_trailing(config.update_debounce, void(M.update))
diff --git a/lua/gitsigns/util.lua b/lua/gitsigns/util.lua
index fc065bc..95d4d20 100644
--- a/lua/gitsigns/util.lua
+++ b/lua/gitsigns/util.lua
@@ -107,4 +107,28 @@ function M.copy_array(x)
    return r
 end
 
+
+function M.strip_cr(xs0)
+   for i = 1, #xs0 do
+      if xs0[i]:sub(-1) ~= '\r' then
+
+         return xs0
+      end
+   end
+
+   local xs = vim.deepcopy(xs0)
+   for i = 1, #xs do
+      xs[i] = xs[i]:sub(1, -2)
+   end
+   return xs
+end
+
+function M.calc_base(base)
+   if base and base:sub(1, 1):match('[~\\^]') then
+      base = 'HEAD' .. base
+   end
+   return base
+end
+
+
 return M
diff --git a/teal/gitsigns/actions.tl b/teal/gitsigns/actions.tl
index 77c9523..e94c2a7 100644
--- a/teal/gitsigns/actions.tl
+++ b/teal/gitsigns/actions.tl
@@ -47,7 +47,7 @@ local record M
   blame_line         : function -- function()
   change_base        : function(base: string, global: boolean)
   reset_base         : function(global: boolean)
-  diffthis           : function -- function(base: string)
+  diffthis           : function(base: string)
 
   record QFListOpts
     use_location_list: boolean
@@ -115,6 +115,13 @@ local function get_cursor_hunk(bufnr: integer, hunks: {Hunk}): Hunk, integer
   return gs_hunks.find_hunk(lnum, hunks)
 end
 
+local function update(bufnr: integer)
+  manager.update(bufnr)
+  if vim.wo.diff then
+    require('gitsigns.diffthis').update(bufnr)
+  end
+end
+
 --- Stage the hunk at the cursor position, or all lines in the
 --- given range. If {range} is provided, all lines in the given
 --- range are staged. This supports partial-hunks, meaning if a
@@ -165,7 +172,7 @@ M.stage_hunk = mk_repeatable(void(function(range: {integer, integer})
   table.insert(bcache.staged_diffs, hunk)
 
   bcache.compare_text = nil -- Invalidate
-  manager.update(bufnr)
+  update(bufnr)
 end))
 
 --- Reset the lines of the hunk at the cursor position, or all
@@ -249,7 +256,7 @@ M.undo_stage_hunk = void(function()
 
   bcache.git_obj:stage_hunks({hunk}, true)
   bcache.compare_text = nil -- Invalidate
-  manager.update(bufnr)
+  update(bufnr)
 end)
 
 --- Stage all hunks in current buffer.
@@ -283,7 +290,7 @@ M.stage_buffer = void(function()
   end
   bcache.compare_text = nil -- Invalidate
 
-  manager.update(bufnr)
+  update(bufnr)
 end)
 
 --- Unstage all hunks for current buffer in the index. Note:
@@ -311,7 +318,7 @@ M.reset_buffer_index = void(function()
   bcache.compare_text = nil -- Invalidate
 
   scheduler()
-  manager.update(bufnr)
+  update(bufnr)
 end)
 
 local function process_nav_opts(opts: NavHunkOpts)
@@ -451,22 +458,6 @@ local function noautocmd(f: function()): function()
   end
 end
 
--- Strip '\r' from the EOL of each line only if all lines end with '\r'
-local function strip_cr(xs0: {string}): {string}
-  for i = 1, #xs0 do
-    if xs0[i]:sub(-1) ~= '\r' then
-      -- don't strip, return early
-      return xs0
-    end
-  end
-  -- all lines end with '\r', need to strip
-  local xs = vim.deepcopy(xs0)
-  for i = 1, #xs do
-    xs[i] = xs[i]:sub(1, -2)
-  end
-  return xs
-end
-
 --- Preview the hunk at the cursor position in a floating
 --- window.
 M.preview_hunk = noautocmd(function()
@@ -479,7 +470,7 @@ M.preview_hunk = noautocmd(function()
 
   local hlines = gs_hunks.patch_lines(hunk)
   if vim.bo[cbuf].fileformat == 'dos' then
-    hlines = strip_cr(hlines)
+    hlines = util.strip_cr(hlines)
   end
 
   local lines = {
@@ -677,17 +668,10 @@ M.blame_line = void(function(opts: boolean | BlameOpts)
   end
 end)
 
-local function calc_base(base: string): string
-  if base and base:sub(1, 1):match('[~\\^]') then
-    base = 'HEAD'..base
-  end
-  return base
-end
-
 local function update_buf_base(buf: integer, bcache: CacheEntry, base: string)
     bcache.base = base
     bcache.compare_text = nil
-    manager.update(buf, bcache)
+    update(buf)
 end
 
 --- Change the base revision to diff against. If {base} is not
@@ -724,7 +708,7 @@ end
 --- For a more complete list of ways to specify bases, see
 --- |gitsigns-revision|.
 M.change_base = void(function(base: string, global: boolean)
-  base = calc_base(base)
+  base = util.calc_base(base)
 
   if global then
     config.base = base
@@ -752,6 +736,9 @@ end
 --- Perform a |vimdiff| on the given file with {base} if it is
 --- given, or with the currently set base (index by default).
 ---
+--- If {base} is the index, then the opened diff buffer is editable
+--- and any written changes will update the index accordingly.
+---
 --- Examples: >
 ---   " Diff against the index
 ---   :Gitsigns diffthis
@@ -765,61 +752,10 @@ end
 ---
 --- Attributes: ~
 ---     {async}
-M.diffthis = void(function(base: string)
-  local bufnr = current_buf()
-  local bcache = cache[bufnr]
-  if not bcache then return end
-
-  if api.nvim_win_get_option(0, 'diff') then return end
-
-  local ff = vim.bo[bufnr].fileformat
-
-  local text: {string}
-  local err: string
-  local comp_rev = bcache:get_compare_rev(calc_base(base))
-
-  if base then
-    text, err = bcache.git_obj:get_show_text(comp_rev)
-    if ff == 'dos' then
-      text = strip_cr(text)
-    end
-    if err then
-      print(err)
-      return
-    end
-    scheduler()
-  else
-    text = bcache:get_compare_text()
-  end
-
-  local ft = api.nvim_buf_get_option(bufnr, 'filetype')
-
-  local bufname = string.format(
-    'gitsigns://%s/%s',
-    bcache.git_obj.repo.gitdir,
-    comp_rev..':'..bcache.git_obj.relpath
-  )
-
-  vim.cmd'diffthis'
-
-  vim.cmd(table.concat({
-    'keepalt', 'aboveleft',
-    config.diff_opts.vertical and 'vertical' or '',
-    'split', bufname
-  }, ' '))
-
-  local dbuf = current_buf()
-
-  api.nvim_buf_set_option(dbuf, 'modifiable', true)
-  util.set_lines(dbuf, 0, -1, text)
-  api.nvim_buf_set_option(dbuf, 'modifiable', false)
-
-  api.nvim_buf_set_option(dbuf, 'filetype', ft)
-  api.nvim_buf_set_option(dbuf, 'buftype', 'nowrite')
-  api.nvim_buf_set_option(dbuf, 'bufhidden', 'wipe')
-
-  vim.cmd'diffthis'
-end)
+M.diffthis = function(base: string)
+  local diffthis = require('gitsigns.diffthis')
+  diffthis.run(base, config.diff_opts.vertical)
+end
 
 local function hunks_to_qflist(buf_or_filename: number|string, hunks: {Hunk}, qflist: {vim.fn.QFItem})
   for i, hunk in ipairs(hunks) do
diff --git a/teal/gitsigns/async.tl b/teal/gitsigns/async.tl
index df3e5b9..71b1a10 100644
--- a/teal/gitsigns/async.tl
+++ b/teal/gitsigns/async.tl
@@ -5,11 +5,13 @@ local type fun1   = function <A1>          (A1)
 local type fun2   = function <A1,A2>       (A1,A2)
 local type fun2_2 = function <A1,A2,R1,R2> (A1,A2)   : R1,R2
 local type fun3   = function <A1,A2,A3>    (A1,A2,A3)
+local type fun4   = function <A1,A2,A3,A4> (A1,A2,A3,A4)
 
 local record Async
   void: function       (fun0       ): fun0
   void: function<A1>   (fun1<A1>   ): fun1<A1>
   void: function<A1,A2>(fun2<A1,A2>): fun2<A1,A2>
+  void: function<A1,A2,A3,A4>(fun4<A1,A2,A3,A4>): fun4<A1,A2,A3,A4>
 
   wrap: function<A1,A2,R1,R2>(function(A1,A2,   function(R1,R2)), integer): fun2_2 <A1,A2,R1,R2>
   wrap: function<A1,A2,A3>   (function(A1,A2,A3,function())     , integer): fun3   <A1,A2,A3>
diff --git a/teal/gitsigns/cache.tl b/teal/gitsigns/cache.tl
index be5fd9c..83565da 100644
--- a/teal/gitsigns/cache.tl
+++ b/teal/gitsigns/cache.tl
@@ -18,6 +18,7 @@ local record M
 
     get_compare_rev: function(CacheEntry, base: string): string
     get_compare_text: function(self: CacheEntry): {string}
+    get_diffthis_bufname: function(self: CacheEntry, rev: string): string
     new: function(CacheEntry): CacheEntry
     destroy: function(CacheEntry)
   end
@@ -48,6 +49,15 @@ CacheEntry.get_compare_rev = function(self: CacheEntry, base: string): string
   return string.format(':%d', stage)
 end
 
+CacheEntry.get_diffthis_bufname = function(self: CacheEntry, rev: string): string
+  rev = rev or self:get_compare_rev()
+  return string.format(
+    'gitsigns://%s/%s',
+    self.git_obj.repo.gitdir,
+    rev..':'..self.git_obj.relpath
+  )
+end
+
 CacheEntry.get_compare_text = function(self: CacheEntry): {string}
   if self.compare_text then
     return self.compare_text
diff --git a/teal/gitsigns/debounce.tl b/teal/gitsigns/debounce.tl
index d3273e3..7b734d1 100644
--- a/teal/gitsigns/debounce.tl
+++ b/teal/gitsigns/debounce.tl
@@ -51,7 +51,7 @@ end
 --
 --@param fn (function) Function to throttle
 --@returns (function) throttled function.
-function M.throttle_by_id(fn: function): function
+function M.throttle_by_id(fn: function, schedule: boolean): function
   local scheduled: {any:boolean} = {}
   local running: {any:boolean} = {}
   return function(id: any, ...)
@@ -59,7 +59,9 @@ function M.throttle_by_id(fn: function): function
       -- If fn is already scheduled, then drop
       return
     end
-    scheduled[id] = true
+    if not running[id] or schedule then
+      scheduled[id] = true
+    end
     if running[id] then
       return
     end
diff --git a/teal/gitsigns/diffthis.tl b/teal/gitsigns/diffthis.tl
new file mode 100644
index 0000000..76c7290
--- /dev/null
+++ b/teal/gitsigns/diffthis.tl
@@ -0,0 +1,162 @@
+local api = vim.api
+
+local void      = require('gitsigns.async').void
+local scheduler = require('gitsigns.async').scheduler
+local awrap     = require('gitsigns.async').wrap
+
+local gs_cache   = require('gitsigns.cache')
+local cache      = gs_cache.cache
+local CacheEntry = gs_cache.CacheEntry
+
+local nvim    = require('gitsigns.nvim')
+local util    = require('gitsigns.util')
+local manager = require('gitsigns.manager')
+
+local throttle_by_id = require('gitsigns.debounce').throttle_by_id
+
+local input = awrap(vim.ui.input, 2)
+
+local record M
+  run: function
+  update: function
+end
+
+local bufread = void(function(bufnr: integer, dbufnr: integer, base: string, bcache: CacheEntry)
+  local comp_rev = bcache:get_compare_rev(util.calc_base(base))
+  local text: {string}
+  if util.calc_base(base) == util.calc_base(bcache.base) then
+    text = bcache:get_compare_text()
+  else
+    local err: string
+    text, err = bcache.git_obj:get_show_text(comp_rev)
+    if err then
+      print(err)
+      return
+    end
+    if vim.bo[bufnr].fileformat == 'dos' then
+      text = util.strip_cr(text)
+    end
+    scheduler()
+  end
+
+  local modifiable = vim.bo[dbufnr].modifiable
+  vim.bo[dbufnr].modifiable = true
+  util.set_lines(dbufnr, 0, -1, text)
+
+  vim.bo[dbufnr].modifiable = modifiable
+  vim.bo[dbufnr].modified = false
+  vim.bo[dbufnr].filetype = vim.bo[bufnr].filetype
+  vim.bo[dbufnr].bufhidden = 'wipe'
+
+  vim.cmd'diffthis'
+end)
+
+local bufwrite = void(function(bufnr: integer, dbufnr: integer, base: string, bcache: CacheEntry)
+  local buftext = util.buf_lines(dbufnr)
+  bcache.git_obj:stage_lines(buftext)
+  vim.bo[dbufnr].modified = false
+  -- If diff buffer base matches the bcache base then also update the
+  -- signs.
+  if util.calc_base(base) == util.calc_base(bcache.base) then
+    bcache.compare_text = buftext
+    manager.update(bufnr, bcache)
+  end
+end)
+
+M.run = void(function(base: string, vertical: boolean)
+  local bufnr = vim.api.nvim_get_current_buf()
+  local bcache = cache[bufnr]
+  if not bcache then
+    return
+  end
+
+  if vim.wo.diff then
+    return
+  end
+
+  local comp_rev = bcache:get_compare_rev(util.calc_base(base))
+  local bufname = bcache:get_diffthis_bufname(comp_rev)
+
+  vim.cmd'diffthis'
+
+  vim.cmd(table.concat({
+    'keepalt', 'aboveleft',
+    vertical and 'vertical' or '',
+    'split', bufname
+  }, ' '))
+
+  local dbuf = vim.api.nvim_get_current_buf()
+
+  bufread(bufnr, dbuf, base, bcache)
+
+  if comp_rev == ':0' then
+    vim.bo[dbuf].buftype = 'acwrite'
+
+    nvim.autocmd('BufReadCmd', {
+      group = 'gitsigns',
+      buffer = dbuf,
+      callback = function()
+        bufread(bufnr, dbuf, base, bcache)
+      end
+    })
+
+    nvim.autocmd('BufWriteCmd', {
+      group = 'gitsigns',
+      buffer = dbuf,
+      callback = function()
+        bufwrite(bufnr, dbuf, base, bcache)
+      end
+    })
+  else
+    vim.bo[dbuf].buftype = 'nowrite'
+    vim.bo[dbuf].modifiable = false
+  end
+end)
+
+
+local function should_reload(bufnr: integer): boolean
+  if not vim.bo[bufnr].modified then
+    return true
+  end
+  local response: string
+  while not vim.tbl_contains({'O', 'L'}, response) do
+    response = input{
+      prompt = 'Warning: The git index has changed and the buffer was changed as well. [O]K, (L)oad File:'
+    }
+  end
+  return response == 'L'
+end
+
+-- This function needs to be throttled as there is a call to vim.ui.input
+M.update = throttle_by_id(void(function(bufnr: integer)
+  if not vim.wo.diff then
+    return
+  end
+
+  local bcache = cache[bufnr]
+
+  -- Note this will be the bufname for the currently set base
+  -- which are the only ones we want to update
+  local bufname = bcache:get_diffthis_bufname()
+
+  for _, w in ipairs(api.nvim_list_wins()) do
+    if api.nvim_win_is_valid(w) then
+      local b = api.nvim_win_get_buf(w)
+      local bname = api.nvim_buf_get_name(b)
+      if bname == bufname or vim.startswith(bname, 'fugitive://') then
+        if should_reload(b) then
+          api.nvim_buf_call(b, function(): nil
+
+
+
+
+            vim.cmd('doautocmd BufReadCmd')
+            vim.cmd('diffthis')
+          end)
+        end
+      end
+    end
+  end
+end))
+
+return M
diff --git a/teal/gitsigns/git.tl b/teal/gitsigns/git.tl
index f9c367a..b8e2d9e 100644
--- a/teal/gitsigns/git.tl
+++ b/teal/gitsigns/git.tl
@@ -103,6 +103,7 @@ local record M
     get_show_text        : function(Obj, string): {string}, string
     ensure_file_in_index : function(Obj)
     stage_hunks          : function(Obj, {Hunk}, boolean)
+    stage_lines          : function(Obj, {string})
     has_moved            : function(Obj): string
     new                  : function(string): Obj
   end
@@ -451,7 +452,7 @@ Obj.ensure_file_in_index = function(self: Obj)
     else
       -- Update the index with the common ancestor (stage 1) which is what bcache
       -- stores
-      local info = table.concat({self.mode_bits, self.object_name, self.relpath}, ',')
+      local info = string.format('%s,%s,%s', self.mode_bits, self.object_name, self.relpath)
       self:command{'update-index', '--add', '--cacheinfo', info}
     end
 
@@ -459,6 +460,18 @@ Obj.ensure_file_in_index = function(self: Obj)
   end
 end
 
+Obj.stage_lines = function(self: Obj, lines: {string})
+  local stdout = self:command({
+    'hash-object', '-w', '--path', self.relpath, '--stdin'
+  }, { writer = lines })
+
+  local new_object = stdout[1]
+
+  self:command{
+    'update-index', '--cacheinfo', string.format('%s,%s,%s', self.mode_bits, new_object, self.relpath)
+  }
+end
+
 Obj.stage_hunks = function(self: Obj, hunks: {Hunk}, invert: boolean)
   self:ensure_file_in_index()
   self:command({
diff --git a/teal/gitsigns/manager.tl b/teal/gitsigns/manager.tl
index 787c014..bf6652c 100644
--- a/teal/gitsigns/manager.tl
+++ b/teal/gitsigns/manager.tl
@@ -328,7 +328,7 @@ end
 -- Since updates are asynchronous we need to make sure an update isn't performed
 -- whilst another one is in progress. If this happens then schedule another
 -- update after the current one has completed.
-M.update = throttle_by_id(update0) as function(integer, CacheEntry)
+M.update = throttle_by_id(update0, true) as function(integer, CacheEntry)
 
 M.setup = function()
   M.update_debounced = debounce_trailing(config.update_debounce, void(M.update)) as function(integer)
diff --git a/teal/gitsigns/util.tl b/teal/gitsigns/util.tl
index 8920d37..1bacf82 100644
--- a/teal/gitsigns/util.tl
+++ b/teal/gitsigns/util.tl
@@ -107,4 +107,28 @@ function M.copy_array<T>(x: {T}): {T}
   return r
 end
 
+-- Strip '\r' from the EOL of each line only if all lines end with '\r'
+function M.strip_cr(xs0: {string}): {string}
+  for i = 1, #xs0 do
+    if xs0[i]:sub(-1) ~= '\r' then
+      -- don't strip, return early
+      return xs0
+    end
+  end
+  -- all lines end with '\r', need to strip
+  local xs = vim.deepcopy(xs0)
+  for i = 1, #xs do
+    xs[i] = xs[i]:sub(1, -2)
+  end
+  return xs
+end
+
+function M.calc_base(base: string): string
+  if base and base:sub(1, 1):match('[~\\^]') then
+    base = 'HEAD'..base
+  end
+  return base
+end
+
+
 return M
diff --git a/types/types.d.tl b/types/types.d.tl
index 0fb45c1..3f937ac 100644
--- a/types/types.d.tl
+++ b/types/types.d.tl
@@ -137,7 +137,7 @@ local record api
   nvim_list_runtime_paths: function(): {string}
   nvim_list_tabpages: function(): {any}
   nvim_list_uis: function(): any
-  nvim_list_wins: function(): {number}
+  nvim_list_wins: function(): {integer}
   nvim_load_context: function({string:any}): any
   nvim_open_win: function(number, boolean, {string:any}): integer
   nvim_out_write: function(string)
@@ -178,7 +178,7 @@ local record api
   nvim_win_call: function<T>(number, (function(): T)): T
   nvim_win_close: function(number, boolean)
   nvim_win_del_var: function(number, string)
-  nvim_win_get_buf: function(number): number
+  nvim_win_get_buf: function(integer): integer
   nvim_win_get_config: function(number): {string:any}
   nvim_win_get_cursor: function(number): {integer}
   nvim_win_get_height: function(integer): integer
@@ -209,6 +209,7 @@ global record vim
     executable: function(string): integer
     expand: function(string): string
     getcwd: function(): string
+    input: function(string, string): string
 
     record QFItem
       bufnr: integer
@@ -290,6 +291,20 @@ global record vim
   record BufOption
     {BufOption}
     fileformat: string
+    filetype: string
+    modifiable: boolean
+    modified: boolean
+
+    enum BufHidden
+      '' 'hide' 'unload' 'delete' 'wipe'
+    end
+
+    bufhidden: BufHidden
+
+    enum BufType
+      '' 'acwrite' 'help' 'nofile' 'nowrite' 'quickfix' 'terminal' 'prompt'
+    end
+    buftype: BufType
   end
 
   bo: BufOption
@@ -489,6 +504,10 @@ global record vim
 
   wait: function(number, function, number, boolean)
 
+  record ui
+    input: function({string:any}, function(string))
+  end
+
   record VersionDetails
     api_compatible: integer
     api_level: integer