patch 8.2.3545: setcellwidths() may make 'listchars' or 'fillchars' invalid

Problem:    setcellwidths() may make 'listchars' or 'fillchars' invalid.
Solution:   Check the value and give an error. (closes #9024)

runtime/doc/eval.txt

@@ -9648,6 +9648,9 @@ setcellwidths({list})					*setcellwidths()*
 		range overlaps with another.
 		Only characters with value 0x100 and higher can be used.
 
+		If the new value causes 'fillchars' or 'listchars' to become
+		invalid it is rejected and an error is given.
+
 		To clear the overrides pass an empty list: >
 		   setcellwidths([]);
 <		You can use the script $VIMRUNTIME/tools/emoji_list.vim to see

src/errors.h

@@ -160,6 +160,10 @@ EXTERN char e_list_value_does_not_have_enough_items[]
 	INIT(= N_("E711: List value does not have enough items"));
 EXTERN char e_cannot_slice_dictionary[]
 	INIT(= N_("E719: Cannot slice a Dictionary"));
+EXTERN char e_conflicts_with_value_of_listchars[]
+	INIT(= N_("E834: Conflicts with value of 'listchars'"));
+EXTERN char e_conflicts_with_value_of_fillchars[]
+	INIT(= N_("E835: Conflicts with value of 'fillchars'"));
 EXTERN char e_assert_fails_second_arg[]
 	INIT(= N_("E856: \"assert_fails()\" second argument must be a string or a list with one or two strings"));
 EXTERN char e_using_invalid_value_as_string_str[]

src/mbyte.c

@@ -5510,6 +5510,8 @@ f_setcellwidths(typval_T *argvars, typval_T *rettv UNUSED)
     int		    i;
     listitem_T	    **ptrs;
     cw_interval_T   *table;
+    cw_interval_T   *cw_table_save;
+    size_t	    cw_table_size_save;
 
     if (in_vim9script() && check_for_list_arg(argvars, 0) == FAIL)
 	return;
@@ -5620,9 +5622,41 @@ f_setcellwidths(typval_T *argvars, typval_T *rettv UNUSED)
     }
 
     vim_free(ptrs);
-    vim_free(cw_table);
+
+    cw_table_save = cw_table;
+    cw_table_size_save = cw_table_size;
     cw_table = table;
     cw_table_size = l->lv_len;
+
+    // Check that the new value does not conflict with 'fillchars' or
+    // 'listchars'.
+    if (set_chars_option(curwin, &p_fcs) != NULL)
+    {
+	emsg(_(e_conflicts_with_value_of_fillchars));
+	cw_table = cw_table_save;
+	cw_table_size = cw_table_size_save;
+	vim_free(table);
+	return;
+    }
+    else
+    {
+	tabpage_T	*tp;
+	win_T	*wp;
+
+	FOR_ALL_TAB_WINDOWS(tp, wp)
+	{
+	    if (set_chars_option(wp, &wp->w_p_lcs) != NULL)
+	    {
+		emsg((e_conflicts_with_value_of_listchars));
+		cw_table = cw_table_save;
+		cw_table_size = cw_table_size_save;
+		vim_free(table);
+		return;
+	    }
+	}
+    }
+
+    vim_free(cw_table_save);
 }
 
     void

src/optionstr.c

@@ -871,7 +871,7 @@ did_set_string_option(
 	if (check_opt_strings(p_ambw, p_ambw_values, FALSE) != OK)
 	    errmsg = e_invarg;
 	else if (set_chars_option(curwin, &p_fcs) != NULL)
-	    errmsg = _("E835: Conflicts with value of 'fillchars'");
+	    errmsg = _(e_conflicts_with_value_of_fillchars);
 	else
 	{
 	    tabpage_T	*tp;
@@ -881,7 +881,7 @@ did_set_string_option(
 	    {
 		if (set_chars_option(wp, &wp->w_p_lcs) != NULL)
 		{
-		    errmsg = _("E834: Conflicts with value of 'listchars'");
+		    errmsg = _(e_conflicts_with_value_of_listchars);
 		    goto ambw_end;
 		}
 	    }

src/testdir/test_utf8.vim

@@ -185,6 +185,16 @@ func Test_setcellwidths()
   call assert_fails('call setcellwidths([[0x111, 0x122, 1], [0x122, 0x123, 2]])', 'E1113:')
 
   call assert_fails('call setcellwidths([[0x33, 0x44, 2]])', 'E1114:')
+
+  set listchars=tab:--\\u2192
+  call assert_fails('call setcellwidths([[0x2192, 0x2192, 2]])', 'E834:')
+
+  set fillchars=stl:\\u2501
+  call assert_fails('call setcellwidths([[0x2501, 0x2501, 2]])', 'E835:')
+
+  set listchars&
+  set fillchars&
+  call setcellwidths([])
 endfunc
 
 func Test_print_overlong()

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3545,
 /**/
     3544,
 /**/