vim-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 vim/vim#9024)
94358a1e6e

Cherry-pick f_setcellwidths() change from patch 9.0.0036.
Cherry-pick 'ambiwidth' docs update from runtime update 079ba76ae7a7.

runtime/doc/builtin.txt

@@ -6837,6 +6837,9 @@ 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([]);
 

runtime/doc/options.txt

@@ -591,6 +591,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 	"double":	Use twice the width of ASCII characters.
 							*E834* *E835*
 	The value "double" cannot be used if 'listchars' or 'fillchars'
+	contains a character that would be double width.  These errors may
+	also be given when calling setcellwidths().
 
 	The values are overruled for characters specified with
 	|setcellwidths()|.

src/nvim/globals.h

@@ -1000,6 +1000,11 @@ EXTERN char e_fnametoolong[] INIT(= N_("E856: Filename too long"));
 EXTERN char e_float_as_string[] INIT(= N_("E806: using Float as a String"));
 EXTERN char e_cannot_edit_other_buf[] INIT(= N_("E788: Not allowed to edit another buffer now"));
 
+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_autocmd_err[] INIT(= N_("E5500: autocmd has thrown an exception: %s"));
 EXTERN char e_cmdmap_err[] INIT(= N_("E5520: <Cmd> mapping must end with <CR>"));
 EXTERN char e_cmdmap_repeated[]

src/nvim/mbyte.c

@@ -2838,7 +2838,38 @@ void f_setcellwidths(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   }
 
   xfree(ptrs);
-  xfree(cw_table);
+
+  cw_interval_T *const cw_table_save = cw_table;
+  const size_t cw_table_size_save = cw_table_size;
   cw_table = table;
   cw_table_size = (size_t)tv_list_len(l);
+
+  // Check that the new value does not conflict with 'fillchars' or
+  // 'listchars'.
+  char *error = NULL;
+  if (set_chars_option(curwin, &p_fcs, false) != NULL) {
+    error = e_conflicts_with_value_of_fillchars;
+  } else if (set_chars_option(curwin, &p_lcs, false) != NULL) {
+    error = e_conflicts_with_value_of_listchars;
+  } else {
+    FOR_ALL_TAB_WINDOWS(tp, wp) {
+      if (set_chars_option(wp, &wp->w_p_lcs, false) != NULL) {
+        error = e_conflicts_with_value_of_listchars;
+        break;
+      }
+      if (set_chars_option(wp, &wp->w_p_fcs, false) != NULL) {
+        error = e_conflicts_with_value_of_fillchars;
+        break;
+      }
+    }
+  }
+  if (error != NULL) {
+    emsg(_(error));
+    cw_table = cw_table_save;
+    cw_table_size = cw_table_size_save;
+    xfree(table);
+    return;
+  }
+
+  xfree(cw_table_save);
 }

src/nvim/option.c

@@ -2580,11 +2580,11 @@ static char *did_set_string_option(int opt_idx, char_u **varp, char_u *oldval, c
     } else {
       FOR_ALL_TAB_WINDOWS(tp, wp) {
         if (set_chars_option(wp, &wp->w_p_lcs, true) != NULL) {
-          errmsg = _("E834: Conflicts with value of 'listchars'");
+          errmsg = _(e_conflicts_with_value_of_listchars);
           goto ambw_end;
         }
         if (set_chars_option(wp, &wp->w_p_fcs, true) != NULL) {
-          errmsg = _("E835: Conflicts with value of 'fillchars'");
+          errmsg = _(e_conflicts_with_value_of_fillchars);
           goto ambw_end;
         }
       }
@@ -3605,7 +3605,7 @@ static int get_encoded_char_adv(char_u **p)
 ///
 /// @param varp either &curwin->w_p_lcs or &curwin->w_p_fcs
 /// @return error message, NULL if it's OK.
-static char *set_chars_option(win_T *wp, char_u **varp, bool set)
+char *set_chars_option(win_T *wp, char_u **varp, bool set)
 {
   int round, i, len, len2, entries;
   char_u *p, *s;

src/nvim/testdir/test_utf8.vim

@@ -173,6 +173,16 @@ 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()