FIX: it was possible to modify a hidden value using extend

resolves: Oldes/Rebol-issues#2532

Author: Oldes

src/core/t-object.c

@@ -84,7 +84,10 @@ static void Extend_Obj(REBSER *obj, REBVAL *key, REBVAL *value)
 		if (index) {
 			if (!value) return;
 			val = FRM_VALUE(obj, index);
-			if (VAL_PROTECTED(val)) Trap1(RE_LOCKED_WORD, val);
+			if (GET_FLAGS(VAL_OPTS(FRM_WORD(obj, index)), OPTS_HIDE, OPTS_LOCK)) {
+				if (VAL_PROTECTED(val)) Trap1(RE_LOCKED_WORD, val);
+				Trap0(RE_HIDDEN);
+			}
 		} else {
 			Expand_Frame(obj, 1, 1); // copy word table also
 			val = Append_Frame(obj, 0, VAL_WORD_SYM(key));

src/tests/units/object-test.r3

@@ -80,15 +80,19 @@ Rebol [
 		]
 	--test-- "extend object with hidden value"
 	;@@ https://github.com/Oldes/Rebol-issues/issues/1140
-		obj: object [a: 1 protect/hide 'a]
+	;@@ https://github.com/Oldes/Rebol-issues/issues/2532
+		obj: object [a: 1 protect/hide 'a test: does [a]]
 		--assert all [
 			error? e: try [extend obj 'a 2]
 			e/id = 'hidden
+			obj/test == 1
 		]
 		--assert all [
 			error? e: try [append obj [a: 2]]
 			e/id = 'hidden
+			obj/test == 1
 		]
+
 	--test-- "append/part object!"
 	;@@ https://github.com/Oldes/Rebol-issues/issues/1754
 		--assert []          == body-of append/part make object! [] [a 1 b 2 c 3] 1