Bind trait props/consts before parent class

This more accurately matches the "copy & paste" semantics described in the
documentation. The same could be done for methods. However, abstract trait
methods diverge from this behavior, given that a parent method can satisfy trait
methods used in the child. In that case, the method is not copied, but the check
must be performed after the parent has been bound. For now, just bother with
properties and constants.

Fixes GH-15753

Author: iluuu1994

Zend/tests/traits/constant_015.phpt

@@ -15,18 +15,6 @@ class DerivedClass1 extends BaseClass1 {
     use TestTrait1;
 }
 
-trait TestTrait2 {
-    public final const Constant = 123;
-}
-
-class BaseClass2 {
-    public final const Constant = 456;
-}
-
-class DerivedClass2 extends BaseClass2 {
-    use TestTrait2;
-}
-
 ?>
 --EXPECTF--
-Fatal error: BaseClass2 and TestTrait2 define the same constant (Constant) in the composition of DerivedClass2. However, the definition differs and is considered incompatible. Class was composed in %s on line %d
+Fatal error: DerivedClass1::Constant cannot override final constant BaseClass1::Constant in %s on line %d

Zend/tests/traits/gh15753.phpt

@@ -0,0 +1,30 @@
+--TEST--
+GH-15753: Overriding readonly properties from traits don't allow assignment from the child
+--FILE--
+<?php
+
+class P {
+    protected readonly int $prop;
+}
+
+trait T {
+    protected readonly int $prop;
+}
+
+class C extends P {
+    use T;
+
+    public function __construct() {
+        $this->prop = 20;
+    }
+}
+
+$c = new C();
+var_dump($c);
+
+?>
+--EXPECT--
+object(C)#1 (1) {
+  ["prop":protected]=>
+  int(20)
+}

Zend/zend_inheritance.c

@@ -2455,7 +2455,7 @@ static void zend_do_bind_traits(zend_class_entry *ce, zend_class_entry **traits)
 	/* complete initialization of trait structures in ce */
 	zend_traits_init_trait_structures(ce, traits, &exclude_tables, &aliases);
 
-	/* first care about all methods to be flattened into the class */
+	/* Flatten all methods into the class */
 	zend_do_traits_method_binding(ce, traits, exclude_tables, aliases);
 
 	if (aliases) {
@@ -2465,10 +2465,6 @@ static void zend_do_bind_traits(zend_class_entry *ce, zend_class_entry **traits)
 	if (exclude_tables) {
 		efree(exclude_tables);
 	}
-
-	/* then flatten the constants and properties into it, to, mostly to notify developer about problems */
-	zend_do_traits_constant_binding(ce, traits);
-	zend_do_traits_property_binding(ce, traits);
 }
 /* }}} */
 
@@ -2990,6 +2986,12 @@ ZEND_API zend_class_entry *zend_do_link_class(zend_class_entry *ce, zend_string
 			zend_enum_register_funcs(ce);
 		}
 
+		if (ce->num_traits) {
+			/* Bind all constants and properties first, so that parent inheritance treats them as if
+			 * they were declared in the child class. */
+			zend_do_traits_constant_binding(ce, traits_and_interfaces);
+			zend_do_traits_property_binding(ce, traits_and_interfaces);
+		}
 		if (parent) {
 			if (!(parent->ce_flags & ZEND_ACC_LINKED)) {
 				add_dependency_obligation(ce, parent);