fix(options): properly free string options

src/nvim/diff.c

@@ -1423,7 +1423,7 @@ void diff_win_options(win_T *wp, int addbuf)
     }
     wp->w_p_fdc_save = vim_strsave(wp->w_p_fdc);
   }
-  xfree(wp->w_p_fdc);
+  free_string_option(wp->w_p_fdc);
   wp->w_p_fdc = (char_u *)xstrdup("2");
   assert(diff_foldcolumn >= 0 && diff_foldcolumn <= 9);
   snprintf((char *)wp->w_p_fdc, STRLEN(wp->w_p_fdc) + 1, "%d", diff_foldcolumn);

src/nvim/terminal.c

@@ -451,15 +451,15 @@ void terminal_enter(void)
   if (save_curwin == curwin->handle) {  // Else: window was closed.
     curwin->w_p_cul = save_w_p_cul;
     if (save_w_p_culopt) {
-      xfree(curwin->w_p_culopt);
+      free_string_option(curwin->w_p_culopt);
       curwin->w_p_culopt = save_w_p_culopt;
     }
     curwin->w_p_culopt_flags = save_w_p_culopt_flags;
     curwin->w_p_cuc = save_w_p_cuc;
     curwin->w_p_so = save_w_p_so;
     curwin->w_p_siso = save_w_p_siso;
   } else if (save_w_p_culopt) {
-    xfree(save_w_p_culopt);
+    free_string_option(save_w_p_culopt);
   }
 
   // draw the unfocused cursor

src/nvim/window.c

@@ -726,31 +726,31 @@ void win_set_minimal_style(win_T *wp)
     wp->w_p_fcs = ((*old == NUL)
                    ? (char_u *)xstrdup("eob: ")
                    : concat_str(old, (char_u *)",eob: "));
-    xfree(old);
+    free_string_option(old);
   }
   if (wp->w_hl_ids[HLF_EOB] != -1) {
     char_u *old = wp->w_p_winhl;
     wp->w_p_winhl = ((*old == NUL)
                      ? (char_u *)xstrdup("EndOfBuffer:")
                      : concat_str(old, (char_u *)",EndOfBuffer:"));
-    xfree(old);
+    free_string_option(old);
   }
 
   // signcolumn: use 'auto'
   if (wp->w_p_scl[0] != 'a' || STRLEN(wp->w_p_scl) >= 8) {
-    xfree(wp->w_p_scl);
+    free_string_option(wp->w_p_scl);
     wp->w_p_scl = (char_u *)xstrdup("auto");
   }
 
   // foldcolumn: use '0'
   if (wp->w_p_fdc[0] != '0') {
-    xfree(wp->w_p_fdc);
+    free_string_option(wp->w_p_fdc);
     wp->w_p_fdc = (char_u *)xstrdup("0");
   }
 
   // colorcolumn: cleared
   if (wp->w_p_cc != NULL && *wp->w_p_cc != NUL) {
-    xfree(wp->w_p_cc);
+    free_string_option(wp->w_p_cc);
     wp->w_p_cc = (char_u *)xstrdup("");
   }
 }

test/functional/ui/float_spec.lua

@@ -18,6 +18,7 @@ local run = helpers.run
 local pcall_err = helpers.pcall_err
 local tbl_contains = global_helpers.tbl_contains
 local curbuf, curwin, curtab = helpers.curbuf, helpers.curwin, helpers.curtab
+local NIL = helpers.NIL
 
 describe('float window', function()
   before_each(function()
@@ -420,6 +421,15 @@ describe('float window', function()
     eq(winids, eval('winids'))
   end)
 
+  it("no segfault when setting minimal style after clearing local 'fillchars' #19510", function()
+    local float_opts = {relative = 'editor', row = 1, col = 1, width = 1, height = 1}
+    local float_win = meths.open_win(0, true, float_opts)
+    meths.win_set_option(float_win, 'fillchars', NIL)
+    float_opts.style = 'minimal'
+    meths.win_set_config(float_win, float_opts)
+    assert_alive()
+  end)
+
   describe('with only one tabpage,', function()
     local float_opts = {relative = 'editor', row = 1, col = 1, width = 1, height = 1}
     local old_buf, old_win