Fix properties_info_table for abstract properties

Fixes GH-19053

Author: iluuu1994

Zend/tests/gh19053.phpt

@@ -0,0 +1,26 @@
+--TEST--
+GH-19053: Incorrect properties_info_table for abstract properties
+--FILE--
+<?php
+
+abstract class GP {
+    public abstract mixed $foo { get; }
+}
+
+class P extends GP {
+    public mixed $foo = 1;
+}
+
+class C extends P {
+    public mixed $foo { get => 2; }
+}
+
+$c = new C;
+var_dump($c);
+
+?>
+--EXPECTF--
+object(C)#%d (0) {
+  ["foo"]=>
+  uninitialized(mixed)
+}

Zend/zend_inheritance.c

@@ -1687,10 +1687,26 @@ void zend_build_properties_info_table(zend_class_entry *ce)
 		}
 	}
 
-	ZEND_HASH_MAP_FOREACH_PTR(&ce->properties_info, prop) {
+	ZEND_HASH_FOREACH_STR_KEY_PTR(&ce->properties_info, zend_string *key, prop) {
 		if (prop->ce == ce && (prop->flags & ZEND_ACC_STATIC) == 0
 		 && !(prop->flags & ZEND_ACC_VIRTUAL)) {
-			uint32_t prop_table_offset = OBJ_PROP_TO_NUM(!(prop->prototype->flags & ZEND_ACC_VIRTUAL) ? prop->prototype->offset : prop->offset);
+			const zend_property_info *root_prop = prop->prototype;
+			if (UNEXPECTED(root_prop->flags & ZEND_ACC_VIRTUAL)) {
+				/* Prototype is virtual, we need to manually hunt down the first backed property. */
+				root_prop = prop;
+				while (true) {
+					zend_class_entry *parent_ce = root_prop->ce->parent;
+					if (!parent_ce) { break; }
+					zend_property_info *parent_prop = zend_hash_find_ptr(&parent_ce->properties_info, key);
+					if (!parent_prop
+					 || parent_prop->prototype != prop->prototype
+					 || (parent_prop->flags & ZEND_ACC_VIRTUAL)) {
+						break;
+					}
+					root_prop = parent_prop;
+				}
+			}
+			uint32_t prop_table_offset = OBJ_PROP_TO_NUM(root_prop->offset);
 			table[prop_table_offset] = prop;
 		}
 	} ZEND_HASH_FOREACH_END();