patch 8.2.1178: Vim9: filter function recognized as command modifier

Problem:    Vim9: filter function recognized as command modifier, leading to a
            crash.
Solution:   Clear cmdmod after freeing items.  Do not recognize a command
            modifier followed by non-white space. (closes #6434)

src/ex_docmd.c

@@ -2750,6 +2750,10 @@ parse_command_modifiers(exarg_T *eap, char **errormsg, int skip_only)
 				if (*p == NUL || ends_excmd(*p))
 				    break;
 			    }
+			    // Avoid that "filter(arg)" is recognized.
+			    if (in_vim9script() && !VIM_ISWHITE(*p))
+				break;
+
 			    if (skip_only)
 				p = skip_vimgrep_pat(p, NULL, NULL);
 			    else
@@ -2904,7 +2908,7 @@ parse_command_modifiers(exarg_T *eap, char **errormsg, int skip_only)
 }
 
 /*
- * Unod and free contents of "cmdmod".
+ * Undo and free contents of "cmdmod".
  */
     void
 undo_cmdmod(exarg_T *eap, int save_msg_scroll)

src/testdir/test_vim9_cmd.vim

@@ -265,6 +265,12 @@ def Test_bar_after_command()
   endif
 enddef
 
+def Test_filter_is_not_modifier()
+  let tags = [{'a': 1, 'b': 2}, {'x': 3, 'y': 4}]
+  filter(tags, { _, v -> has_key(v, 'x') ? 1 : 0 })
+  assert_equal([#{x: 3, y: 4}], tags)
+enddef
+
 def Test_eval_command()
   let from = 3
   let to = 5

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1178,
 /**/
     1177,
 /**/

src/vim9compile.c

@@ -6963,6 +6963,7 @@ compile_def_function(ufunc_T *ufunc, int set_return_type, cctx_T *outer_cctx)
 	}
 	// TODO: use modifiers in the command
 	undo_cmdmod(&ea, save_msg_scroll);
+	CLEAR_FIELD(cmdmod);
 
 	// Skip ":call" to get to the function name.
 	if (checkforcmd(&ea.cmd, "call", 3))