vim-patch:9.0.1036: undo misbehaves when writing from an insert mode mapping

Problem:    Undo misbehaves when writing from an insert mode mapping.
Solution:   Sync undo when writing. (closes vim/vim#11674)

https://github.com/vim/vim/commit/3f8f82772313af9f2417b06651f30988b63e1c96

Co-authored-by: Bram Moolenaar <Bram@vim.org>

3 files changed, 70 insertions, 0 deletions

diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index ac2973ba68..09836e747f 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -908,6 +908,12 @@ check_pum:
       }
       pum_want.active = false;
     }
+
+    if (curbuf->b_u_synced) {
+      // The K_EVENT, K_COMMAND, or K_LUA caused undo to be synced.
+      // Need to save the line for undo before inserting the next char.
+      ins_need_undo = true;
+    }
     break;
 
   case K_HOME:        // <Home>
diff --git a/src/nvim/testdir/test_undo.vim b/src/nvim/testdir/test_undo.vim
index eb47af08d7..ee8b52caaf 100644
--- a/src/nvim/testdir/test_undo.vim
+++ b/src/nvim/testdir/test_undo.vim
@@ -3,6 +3,9 @@
 " undo-able pieces.  Do that by setting 'undolevels'.
 " Also tests :earlier and :later.
 
+source check.vim
+source screendump.vim
+
 func Test_undotree()
   new
 
@@ -773,4 +776,30 @@ func Test_undo_mark()
   bwipe!
 endfunc
 
+func Test_undo_after_write()
+  " use a terminal to make undo work like when text is typed
+  CheckRunVimInTerminal
+
+  let lines =<< trim END
+      edit Xtestfile.txt
+      set undolevels=100 undofile
+      imap . <Cmd>write<CR>
+      write
+  END
+  call writefile(lines, 'Xtest_undo_after_write', 'D')
+  let buf = RunVimInTerminal('-S Xtest_undo_after_write', #{rows: 6})
+
+  call term_sendkeys(buf, "Otest.\<CR>boo!!!\<Esc>")
+  sleep 100m
+  call term_sendkeys(buf, "u")
+  call VerifyScreenDump(buf, 'Test_undo_after_write_1', {})
+
+  call term_sendkeys(buf, "u")
+  call VerifyScreenDump(buf, 'Test_undo_after_write_2', {})
+
+  call StopVimInTerminal(buf)
+  call delete('Xtestfile.txt')
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/test/functional/editor/undo_spec.lua b/test/functional/editor/undo_spec.lua
index a041428cdc..6f9c4506fc 100644
--- a/test/functional/editor/undo_spec.lua
+++ b/test/functional/editor/undo_spec.lua
@@ -9,6 +9,7 @@ local feed = helpers.feed
 local feed_command = helpers.feed_command
 local insert = helpers.insert
 local funcs = helpers.funcs
+local exec = helpers.exec
 
 local function lastmessage()
   local messages = funcs.split(funcs.execute('messages'), '\n')
@@ -67,6 +68,40 @@ describe('u CTRL-R g- g+', function()
     undo_and_redo(4, 'u', '<C-r>', '1')
     undo_and_redo(4, 'g-', 'g+', '1')
   end)
+
+  describe('undo works correctly when writing in Insert mode', function()
+    before_each(function()
+      exec([[
+        edit Xtestfile.txt
+        set undolevels=100 undofile
+        write
+      ]])
+    end)
+
+    after_each(function()
+      command('bwipe!')
+      os.remove('Xtestfile.txt')
+      os.remove('Xtestfile.txt.un~')
+    end)
+
+    -- oldtest: Test_undo_after_write()
+    it('using <Cmd> mapping', function()
+      command('imap . <Cmd>write<CR>')
+      feed('Otest.<CR>boo!!!<Esc>')
+      expect([[
+        test
+        boo!!!
+        ]])
+
+      feed('u')
+      expect([[
+        test
+        ]])
+
+      feed('u')
+      expect('')
+    end)
+  end)
 end)
 
 describe(':undo! command', function()