Address Copilot review comments

- curses_color_content, curses_pair_content: check return value of
  extended_color_content/color_content/extended_pair_content/pair_content
  and return nil on ERR instead of returning uninitialized values
- curses_reset_color_pairs: add curses_stdscr() call for consistency
  with other color APIs
- window_color_set: use wattr_get to preserve existing window attributes
  when calling wattr_set; use NCURSES_PAIRS_T for the pair argument to
  match the ncurses header type in both standard and extended modes;
  fall back to wattr_set without attr preservation if wattr_get is
  unavailable, and to wcolor_set if wattr_set is also unavailable
- extconf.rb: add have_func check for wattr_get
- sample/colors.rb: skip pair 0 (cannot be redefined); use i%colors
  instead of i%256 to handle terminals with fewer than 256 colors

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: shugo

ext/curses/curses.c

@@ -1410,13 +1410,15 @@ curses_color_content(VALUE obj, VALUE color)
 #ifdef HAVE_EXTENDED_COLOR_CONTENT
     {
 	int r, g, b;
-	extended_color_content(NUM2INT(color), &r, &g, &b);
+	if (extended_color_content(NUM2INT(color), &r, &g, &b) == ERR)
+	    return Qnil;
 	return rb_ary_new3(3, INT2FIX(r), INT2FIX(g), INT2FIX(b));
     }
 #else
     {
 	short r, g, b;
-	color_content(NUM2INT(color), &r, &g, &b);
+	if (color_content(NUM2INT(color), &r, &g, &b) == ERR)
+	    return Qnil;
 	return rb_ary_new3(3, INT2FIX(r), INT2FIX(g), INT2FIX(b));
     }
 #endif
@@ -1452,13 +1454,15 @@ curses_pair_content(VALUE obj, VALUE pair)
 #ifdef HAVE_EXTENDED_PAIR_CONTENT
     {
 	int f, b;
-	extended_pair_content(NUM2INT(pair), &f, &b);
+	if (extended_pair_content(NUM2INT(pair), &f, &b) == ERR)
+	    return Qnil;
 	return rb_ary_new3(2, INT2FIX(f), INT2FIX(b));
     }
 #else
     {
 	short f, b;
-	pair_content(NUM2INT(pair), &f, &b);
+	if (pair_content(NUM2INT(pair), &f, &b) == ERR)
+	    return Qnil;
 	return rb_ary_new3(2, INT2FIX(f), INT2FIX(b));
     }
 #endif
@@ -1520,6 +1524,7 @@ curses_support_extended_colors(VALUE obj)
 static VALUE
 curses_reset_color_pairs(VALUE obj)
 {
+    curses_stdscr();
     reset_color_pairs();
     return Qnil;
 }
@@ -2792,7 +2797,16 @@ window_color_set(VALUE obj, VALUE col)
     struct windata *winp;
 
     GetWINDOW(obj, winp);
-#ifdef HAVE_WATTR_SET
+#if defined(HAVE_WATTR_SET) && defined(HAVE_WATTR_GET)
+    /* Use wattr_set to support pair numbers > 255; preserve existing attrs. */
+    {
+	attr_t attrs;
+	NCURSES_PAIRS_T current_pair;
+	if (wattr_get(winp->window, &attrs, &current_pair, NULL) == ERR)
+	    return Qfalse;
+	return (wattr_set(winp->window, attrs, NUM2INT(col), NULL) == OK) ? Qtrue : Qfalse;
+    }
+#elif defined(HAVE_WATTR_SET)
     return (wattr_set(winp->window, 0, NUM2INT(col), NULL) == OK) ? Qtrue : Qfalse;
 #else
     return (wcolor_set(winp->window, NUM2INT(col), NULL) == OK) ? Qtrue : Qfalse;

ext/curses/extconf.rb

@@ -121,7 +121,7 @@ def exec_command(cmd)
               newpad unget_wch get_wch wget_wch PDC_get_key_modifiers
               chgat wchgat newterm
               init_extended_color init_extended_pair extended_color_content
-              extended_pair_content reset_color_pairs wattr_set)
+              extended_pair_content reset_color_pairs wattr_set wattr_get)
     have_func(f) || (have_macro(f, curses) && $defs.push(format("-DHAVE_%s", f.upcase)))
   end
   convertible_int('chtype', [["#undef MOUSE_MOVED\n"]]+curses) or abort

sample/colors.rb

@@ -20,7 +20,8 @@
     addstr extended ? " (extended).\n" : ".\n"
 
     (extended ? [512, color_pairs].min : colors).times { |i|
-      Curses.init_pair(i, i%256, i>=256 ? 8 : 0)
+      next if i == 0
+      Curses.init_pair(i, i % colors, (i / colors) % colors)
       if extended
         # color_pair() encodes into chtype and can't handle pairs > 255;
         # use color_set on stdscr instead, which calls wattr_set internally.