feat(runtime): undotree #35627

Problem
No builtin way to visualize and navigate the undo-tree.

Solution
Include an "opt" plugin.

test/functional/plugin/undotree_spec.lua

@@ -0,0 +1,136 @@
+local t = require('test.testutil')
+local n = require('test.functional.testnvim')()
+
+local clear = n.clear
+local eq = t.eq
+local exec = n.exec
+local api = n.api
+local dedent = t.dedent
+
+---@param reverse_tree {[integer]:integer}
+local function generate_undo_tree_from_rev(reverse_tree)
+  for k, v in ipairs(reverse_tree) do
+    exec('undo ' .. v)
+    api.nvim_buf_set_lines(0, 0, -1, true, { tostring(k) })
+  end
+end
+---@param buf integer
+---@return string
+local function buf_get_lines_and_extmark(buf)
+  local lines = api.nvim_buf_get_lines(buf, 0, -1, true)
+  local ns = api.nvim_create_namespace('nvim.undotree')
+  local extmarks = api.nvim_buf_get_extmarks(buf, ns, 0, -1, { details = true })
+  for i = #extmarks, 1, -1 do
+    local extmark = extmarks[i]
+    ---@type nil,integer,nil,vim.api.keyset.extmark_details
+    local _, row, _, opts = unpack(extmark)
+    local virt_lines = assert(opts.virt_lines)
+    for _, v in ipairs(virt_lines) do
+      local virt_line = v[1][1]
+      table.insert(lines, row + 2, virt_line)
+    end
+  end
+  return table.concat(lines, '\n')
+end
+
+local function strip_time(text)
+  return text:gsub('%s-%(.-%)', '')
+end
+
+describe(':Undotree', function()
+  before_each(function()
+    clear({ args = { '--clean' } })
+    exec 'packadd nvim.undotree'
+  end)
+
+  it('works', function()
+    api.nvim_set_current_line('foo')
+    exec 'Undotree'
+    local buf = api.nvim_get_current_buf()
+    local win = api.nvim_get_current_win()
+    eq(
+      dedent [[
+    *    0
+    *    1]],
+      strip_time(buf_get_lines_and_extmark(buf))
+    )
+    eq(2, api.nvim_win_get_cursor(win)[1])
+    exec 'wincmd w'
+
+    -- Doing changes moves cursor in undotree
+    exec 'undo'
+    eq(1, api.nvim_win_get_cursor(win)[1])
+    api.nvim_set_current_line('bar')
+    eq(3, api.nvim_win_get_cursor(win)[1])
+
+    eq(
+      dedent [[
+    *    0
+    |\
+    | *    1
+    *    2]],
+      strip_time(buf_get_lines_and_extmark(buf))
+    )
+
+    -- Moving the cursor in undotree changes the buffer
+    eq('bar', api.nvim_get_current_line())
+    exec 'wincmd w'
+    exec '2'
+    exec 'wincmd w'
+    eq('foo', api.nvim_get_current_line())
+  end)
+
+  describe('branch+remove is correctly graphed', function()
+    it('when branching left', function()
+      generate_undo_tree_from_rev({ 0, 1, 2, 3, 1, 3, 4, 3, 2, 0 })
+      exec 'Undotree'
+      eq(
+        dedent([[
+        *    0
+        |\
+        | *    1
+        | |\
+        | | *    2
+        | | |\
+        | | | *    3
+        | | | |\
+        | | | | *    4
+        | * | | |    5
+        |  / /| |]] --[[This is the line being tested, e.g. remove&branch left]] .. '\n' .. [[
+        | | | * |    6
+        | | |  /
+        | | | *    7
+        | | *    8
+        | *    9
+        *    10]]),
+        strip_time(buf_get_lines_and_extmark(0))
+      )
+    end)
+
+    it('when branching right', function()
+      generate_undo_tree_from_rev({ 0, 1, 2, 3, 3, 1, 4, 2, 1, 0 })
+      exec 'Undotree'
+      eq(
+        dedent([[
+        *    0
+        |\
+        | *    1
+        | |\
+        | | *    2
+        | | |\
+        | | | *    3
+        | | | |\
+        | | | | *    4
+        | | | * |    5
+        | |\ \  |]] --[[This is the line being tested, e.g. remove&branch right]] .. '\n' .. [[
+        | | * | |    6
+        | |  / /
+        | | | *    7
+        | | *    8
+        | *    9
+        *    10]]),
+        strip_time(buf_get_lines_and_extmark(0))
+      )
+    end)
+  end)
+end)