vim-patch:8.1.0245: calling setline() in TextChangedI autocmd breaks undo

Problem:    Calling setline() in TextChangedI autocmd breaks undo. (Jason
            Felice)
Solution:   Don't save lines for undo when already saved. (closes vim/vim#3291)
91d2e783b4

src/nvim/edit.c

@@ -1392,11 +1392,20 @@ ins_redraw (
       && !pum_visible()) {
     aco_save_T aco;
 
+    // Sync undo when the autocommand calls setline() or append(), so that
+    // it can be undone separately.
+    u_sync_once = 2;
+
     // save and restore curwin and curbuf, in case the autocmd changes them
     aucmd_prepbuf(&aco, curbuf);
     apply_autocmds(EVENT_TEXTCHANGEDI, NULL, NULL, false, curbuf);
     aucmd_restbuf(&aco);
     curbuf->b_last_changedtick = buf_get_changedtick(curbuf);
+
+    if (u_sync_once == 1) {
+      ins_need_undo = true;
+    }
+    u_sync_once = 0;
   }
 
   // Trigger TextChangedP if changedtick differs. When the popupmenu closes

src/nvim/testdir/test_autocmd.vim

@@ -567,7 +567,7 @@ func Test_OptionSet()
   " Cleanup
   au! OptionSet
   for opt in ['nu', 'ai', 'acd', 'ar', 'bs', 'backup', 'cul', 'cp']
-    exe printf(":set %s&vi", opt)
+    exe printf(":set %s&vim", opt)
   endfor
   call test_override('starting', 0)
   delfunc! AutoCommandOptionSet
@@ -1221,3 +1221,29 @@ func Test_ChangedP()
 
   bw!
 endfunc
+
+let g:setline_handled = v:false
+func! SetLineOne()
+  if !g:setline_handled
+    call setline(1, "(x)")
+    let g:setline_handled = v:true
+  endif
+endfunc
+
+func Test_TextChangedI_with_setline()
+  throw 'skipped: Nvim does not support test_override()'
+  new
+  call test_override('char_avail', 1)
+  autocmd TextChangedI <buffer> call SetLineOne()
+  call feedkeys("i(\<CR>\<Esc>", 'tx')
+  call assert_equal('(', getline(1))
+  call assert_equal('x)', getline(2))
+  undo
+  call assert_equal('(', getline(1))
+  call assert_equal('', getline(2))
+  undo
+  call assert_equal('', getline(1))
+
+  call test_override('starting', 0)
+  bwipe!
+endfunc