vim-patch:8.1.2336: when an expr mapping moves the cursor it is not restored

Problem:    When an expr mapping moves the cursor it is not restored.
Solution:   Position the cursor after an expr mapping. (closes vim/vim#5256)
4ebe0e62d0

src/nvim/getchar.c

@@ -1949,8 +1949,10 @@ static int handle_mapping(int *keylenp, bool *timedout, int *mapdepth)
     // expression.  Also save and restore the command line
     // for "normal :".
     if (mp->m_expr) {
-      int save_vgetc_busy = vgetc_busy;
+      const int save_vgetc_busy = vgetc_busy;
       const bool save_may_garbage_collect = may_garbage_collect;
+      const int save_cursor_row = ui_current_row();
+      const int save_cursor_col = ui_current_col();
 
       vgetc_busy = 0;
       may_garbage_collect = false;
@@ -1960,6 +1962,12 @@ static int handle_mapping(int *keylenp, bool *timedout, int *mapdepth)
         save_m_str = vim_strsave(mp->m_str);
       }
       map_str = eval_map_expr(mp, NUL);
+
+      // The mapping may do anything, but we expect it to take care of
+      // redrawing.  Do put the cursor back where it was.
+      ui_cursor_goto(save_cursor_row, save_cursor_col);
+      ui_flush();
+
       vgetc_busy = save_vgetc_busy;
       may_garbage_collect = save_may_garbage_collect;
     } else {

src/nvim/testdir/test_mapping.vim

@@ -1,6 +1,8 @@
 " Tests for mappings and abbreviations
 
 source shared.vim
+source check.vim
+source screendump.vim
 
 func Test_abbreviation()
   " abbreviation with 0x80 should work
@@ -451,6 +453,36 @@ func Test_expr_map_gets_cursor()
   nunmap !
 endfunc
 
+func Test_expr_map_restore_cursor()
+  CheckScreendump
+
+  let lines =<< trim END
+      call setline(1, ['one', 'two', 'three'])
+      2
+      set ls=2
+      hi! link StatusLine ErrorMsg
+      noremap <expr> <C-B> Func()
+      func Func()
+	  let g:on = !get(g:, 'on', 0)
+	  redraws
+	  return ''
+      endfunc
+      func Status()
+	  return get(g:, 'on', 0) ? '[on]' : ''
+      endfunc
+      set stl=%{Status()}
+  END
+  call writefile(lines, 'XtestExprMap')
+  let buf = RunVimInTerminal('-S XtestExprMap', #{rows: 10})
+  call term_wait(buf)
+  call term_sendkeys(buf, "\<C-B>")
+  call VerifyScreenDump(buf, 'Test_map_expr_1', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('XtestExprMap')
+endfunc
+
 " Test for mapping errors
 func Test_map_error()
   call assert_fails('unmap', 'E474:')