feat(preview): improved version of preview_hunk_inline()

(experimental)

Uses a second buffer and a floating window in order to display syntax
highlighting in the deleted lines.

Need to set `_inline2 = true` in `setup()` to enable.

doc/gitsigns.txt

@@ -1068,6 +1068,11 @@ GitSignsDeleteVirtLnInLine
         Used for word diff regions in lines shown by inline `preview_hunk_inline()` or `show_deleted()`.
 
         Fallbacks: `GitSignsDeleteLnInline`
+                                                        *hl-GitSignsVirtLnum*
+GitSignsVirtLnum
+        Used for line numbers in inline hunks previews.
+
+        Fallbacks: `GitSignsDeleteVirtLn`
 
 ==============================================================================
 COMMAND                                                      *gitsigns-command*

teal/gitsigns/actions.tl

@@ -763,13 +763,23 @@ M.preview_hunk_inline = function()
 
   clear_preview_inline(bufnr)
 
+  local winid: integer
   manager.show_added(bufnr, ns_inline, hunk)
-  manager.show_deleted(bufnr, ns_inline, hunk)
+  if config._inline2 then
+    if hunk.removed.count > 0 then
+      winid = manager.show_deleted_in_float(bufnr, ns_inline, hunk)
+    end
+  else
+    manager.show_deleted(bufnr, ns_inline, hunk)
+  end
 
   api.nvim_create_autocmd({ 'CursorMoved', 'InsertEnter' }, {
     buffer = bufnr,
     desc = 'Clear gitsigns inline preview',
     callback = function()
+      if winid then
+        pcall(api.nvim_win_close, winid, true)
+      end
       clear_preview_inline(bufnr)
     end,
     once = true

teal/gitsigns/config.tl

@@ -125,6 +125,7 @@ local record M
     _refresh_staged_on_update: boolean
     _blame_cache: boolean
     _threaded_diff: boolean
+    _inline2: boolean
     _extmark_signs: boolean
 
     _git_version: string
@@ -767,6 +768,14 @@ M.schema = {
     ]]
   },
 
+  _inline2 = {
+    type = 'boolean',
+    default = false,
+    description = [[
+      Enable enhanced version of preview_hunk_inline()
+    ]]
+  },
+
   _extmark_signs = {
     type = 'boolean',
     default = false,

teal/gitsigns/highlight.tl

@@ -147,6 +147,10 @@ M.hls = {
     desc = "Used for word diff regions in lines shown by inline `preview_hunk_inline()` or `show_deleted()`."
   }},
 
+  {GitSignsVirtLnum = {'GitSignsDeleteVirtLn',
+    desc = 'Used for line numbers in inline hunks previews.'
+  }},
+
 }
 
 local function is_hl_set(hl_name: string): boolean

teal/gitsigns/manager.tl

@@ -239,6 +239,97 @@ function M.show_deleted(bufnr: integer, nsd: integer, hunk: Hunk)
   })
 end
 
+function M.show_deleted_in_float(bufnr: integer, nsd: integer, hunk: Hunk): integer
+  local virt_lines = {}
+  for i = 1, hunk.removed.count do
+    virt_lines[i] = { { '', 'Normal' } }
+  end
+
+  local topdelete = hunk.added.start == 0 and hunk.type == 'delete'
+  local virt_lines_above = hunk.type ~= 'delete' or topdelete
+
+  local row = topdelete and 0 or hunk.added.start - 1
+  api.nvim_buf_set_extmark(bufnr, nsd, row, -1, {
+    virt_lines = virt_lines,
+    -- TODO(lewis6991): Note virt_lines_above doesn't work on row 0 neovim/neovim#16166
+    virt_lines_above = virt_lines_above
+  })
+
+  local bcache = cache[bufnr]
+  local pbufnr = api.nvim_create_buf(false, true)
+  api.nvim_buf_set_lines(pbufnr, 0, -1, false, bcache.compare_text)
+
+  local cwin = api.nvim_get_current_win()
+  local width = api.nvim_win_get_width(0)
+
+  local opts: vim.api.WinConfig = {
+    relative = 'win',
+    win = cwin,
+    width = width,
+    height = hunk.removed.count,
+    anchor = 'SW',
+    bufpos = { hunk.added.start, 0 }
+  }
+
+  local bufpos_offset = virt_lines_above and not topdelete and 1 or 0
+  opts.bufpos[1] = opts.bufpos[1] - bufpos_offset
+
+  local winid = api.nvim_open_win(pbufnr, false, opts)
+
+  -- Align buffer text by accounting for differences in the statuscolumn
+  local textoff = vim.fn.getwininfo(cwin)[1].textoff
+  local ptextoff = vim.fn.getwininfo(winid)[1].textoff
+  local col_offset = textoff - ptextoff
+
+  if col_offset ~= 0 then
+    opts.width = opts.width - col_offset
+    opts.bufpos[2] = opts.bufpos[2] + col_offset
+    api.nvim_win_set_config(winid, opts)
+  end
+
+  vim.bo[pbufnr].filetype = vim.bo[bufnr].filetype
+  vim.bo[pbufnr].bufhidden = 'wipe'
+  vim.wo[winid].scrolloff = 0
+  vim.wo[winid].relativenumber = false
+
+  api.nvim_win_call(winid, function(): nil
+    -- Expand folds
+    vim.cmd('normal '..'zR')
+
+    -- Navigate to hunk
+    vim.cmd('normal '..tostring(hunk.removed.start)..'gg')
+    vim.cmd('normal '..vim.api.nvim_replace_termcodes('z<CR>', true, false, true))
+  end)
+
+  -- Apply highlights
+
+  for i = hunk.removed.start, hunk.removed.start + hunk.removed.count do
+    api.nvim_buf_set_extmark(pbufnr, nsd, i - 1, 0, {
+      hl_group = 'GitSignsDeleteVirtLn',
+      hl_eol = true,
+      end_row = i,
+      priority = 1000
+    })
+  end
+
+  local removed_regions =
+    require('gitsigns.diff_int').run_word_diff(hunk.removed.lines, hunk.added.lines)
+
+  for _, region in ipairs(removed_regions) do
+    local start_row = (hunk.removed.start - 1) + (region[1] - 1)
+    local start_col = region[3] - 1
+    local end_col   = region[4] - 1
+    api.nvim_buf_set_extmark(pbufnr, nsd, start_row, start_col, {
+      hl_group = 'GitSignsDeleteVirtLnInline',
+      end_col = end_col,
+      end_row = start_row,
+      priority = 1001
+    })
+  end
+
+  return winid
+end
+
 function M.show_added(bufnr: integer, nsw: integer, hunk: Hunk)
   local start_row = hunk.added.start - 1
 

types/vim.d.tl

@@ -41,6 +41,8 @@ local record M
     {WinOption}
     diff: boolean
     signcolumn: string
+    scrolloff: integer
+    relativenumber: boolean
   end
 
   wo: WinOption

types/vim/api.d.tl

@@ -222,7 +222,27 @@ local record M
   nvim_win_get_width: function(integer): integer
   nvim_win_is_valid: function(number): boolean
   nvim_win_set_buf: function(number, number)
-  nvim_win_set_config: function(number, {string:any})
+
+  record WinConfig
+    bufpos: {integer, integer}
+    virt_lines_above: boolean
+    width: integer
+    height: integer
+    relative: string
+    row: integer
+    col: integer
+    win: integer
+    enum Anchor
+      'NW'
+      'NE'
+      'SW'
+      'SE'
+    end
+    anchor: Anchor
+  end
+
+  nvim_win_set_config: function(number, WinConfig)
+
   nvim_win_set_cursor: function(number, {number})
   nvim_win_set_height: function(number, number)
   nvim_win_set_option: function(number, string, any)

types/vim/fn.d.tl

@@ -77,6 +77,11 @@ local record M
 
   FugitiveReal: function(...: any): string
   FugitiveParse: function(...: any): {string, string}
+
+  record WinInfo
+    textoff: integer
+  end
+  getwininfo: function(integer): {WinInfo}
 end
 
 return M