Add ability to preview hunks in a floating window

README.md

@@ -62,6 +62,7 @@ require('gitsigns').setup {
     ['n <leader>hs'] = '<cmd>lua require"gitsigns".stage_hunk()<CR>',
     ['n <leader>hu'] = '<cmd>lua require"gitsigns".undo_stage_hunk()<CR>',
     ['n <leader>hr'] = '<cmd>lua require"gitsigns".reset_hunk()<CR>',
+    ['n <leader>hp'] = '<cmd>lua require"gitsigns".preview_hunk()<CR>',
   },
   watch_index = {
     interval = 1000
@@ -89,7 +90,7 @@ set statusline+=%{get(b:,'gitsigns_status','')}
 
 - [x] Add action for undoing a stage of a hunk
 - [x] Add action for ~~undoing~~ reseting a hunk
-- [ ] Add action for showing diff (or original text) in a floating window
+- [x] Add action for showing diff (or original text) in a floating window
 - [ ] Add ability to show staged hunks with different signs (maybe in a different sign column?)
 - [x] Add support for repeat.vim
 - [ ] Apply buffer updates incrementally

lua/gitsigns.lua

@@ -7,6 +7,7 @@ local default_config = require('gitsigns/defaults')
 local mk_repeatable = require('gitsigns/repeat').mk_repeatable
 local DB = require('gitsigns/debounce')
 local apply_mappings = require('gitsigns/mappings')
+local popup = require('gitsigns/popup')
 
 local throttle_leading = DB.throttle_leading
 local debounce_trailing = DB.debounce_trailing
@@ -736,6 +737,24 @@ local function setup(cfg)
   vim.cmd('autocmd ExitPre * lua require("gitsigns").detach_all()')
 end
 
+function preview_hunk()
+  local hunk = get_hunk()
+
+  if not hunk then
+    return
+  end
+
+  local winid, bufnr = popup.create(hunk.lines, { relative = 'cursor' })
+
+  vim.fn.nvim_buf_set_option(bufnr, 'filetype', 'diff')
+  vim.fn.nvim_win_set_option(winid, 'number', false)
+  vim.fn.nvim_win_set_option(winid, 'relativenumber', false)
+end
+
+function dump_cache()
+  print(vim.inspect(cache))
+end
+
 return {
   update          = update,
   stage_hunk      = mk_repeatable(stage_hunk),
@@ -743,7 +762,9 @@ return {
   reset_hunk      = mk_repeatable(reset_hunk),
   next_hunk       = next_hunk,
   prev_hunk       = prev_hunk,
+  preview_hunk    = preview_hunk,
   attach          = attach,
   detach_all      = detach_all,
   setup           = setup,
+  dump_cache      = dump_cache
 }

lua/gitsigns/defaults.lua

@@ -17,6 +17,7 @@ return {
     ['n <leader>hs'] = '<cmd>lua require"gitsigns".stage_hunk()<CR>',
     ['n <leader>hu'] = '<cmd>lua require"gitsigns".undo_stage_hunk()<CR>',
     ['n <leader>hr'] = '<cmd>lua require"gitsigns".reset_hunk()<CR>',
+    ['n <leader>hp'] = '<cmd>lua require"gitsigns".preview_hunk()<CR>',
   },
   watch_index = {
     interval = 1000

lua/gitsigns/popup.lua

@@ -0,0 +1,35 @@
+local popup = {}
+
+local api = vim.api
+
+function popup.create(what, vim_options)
+  local bufnr = api.nvim_create_buf(false, true)
+  assert(bufnr, "Failed to create buffer")
+
+  api.nvim_buf_set_lines(bufnr, 0, -1, true, what)
+
+  local width = 0
+  for _, l in pairs(what) do
+    if #l > width then
+      width = #l
+    end
+  end
+
+  local win_id = api.nvim_open_win(bufnr, false, {
+    relative = vim_options.relative,
+    row = 0,
+    col = 0,
+    height = #what,
+    width = width
+  })
+
+  vim.lsp.util.close_preview_autocmd({'CursorMoved', 'CursorMovedI'}, win_id)
+
+  if vim_options.highlight then
+    api.nvim_win_set_option(win_id, 'winhl', string.format('Normal:%s', vim_options.highlight))
+  end
+
+  return win_id, bufnr
+end
+
+return popup