Don't evaluate dynamic constants during trait compatibilty check

Author: nikic

Zend/tests/constexpr/new_trait_prop_compat.phpt

@@ -0,0 +1,26 @@
+--TEST--
+Compatibility of trait properties with new default
+--FILE--
+<?php
+
+class A {
+    // Should not be called.
+    public function __construct() {
+        echo "Constructor\n";
+    }
+}
+
+trait T1 {
+    public $prop = new A;
+}
+trait T2 {
+    public $prop = new A;
+}
+
+class B {
+    use T1, T2;
+}
+
+?>
+--EXPECTF--
+Fatal error: T1 and T2 define the same property ($prop) in the composition of B. However, the definition differs and is considered incompatible. Class was composed in %s on line %d

Zend/zend_inheritance.c

@@ -2062,13 +2062,17 @@ static void zend_do_traits_property_binding(zend_class_entry *ce, zend_class_ent
 							op2 = &traits[i]->default_properties_table[OBJ_PROP_TO_NUM(property_info->offset)];
 						}
 
-						/* if any of the values is a constant, we try to resolve it */
-						if (UNEXPECTED(Z_TYPE_P(op1) == IS_CONSTANT_AST)) {
+						/* If any of the values is a constant, we try to resolve it. Don't resolve
+						 * "dynamic" ASTs, which may have side-effects. For these we assume
+						 * incompatibility. */
+						if (UNEXPECTED(Z_TYPE_P(op1) == IS_CONSTANT_AST)
+								&& !(GC_FLAGS(Z_AST_P(op1)) & IS_AST_DYNAMIC)) {
 							ZVAL_COPY_OR_DUP(&op1_tmp, op1);
 							zval_update_constant_ex(&op1_tmp, ce);
 							op1 = &op1_tmp;
 						}
-						if (UNEXPECTED(Z_TYPE_P(op2) == IS_CONSTANT_AST)) {
+						if (UNEXPECTED(Z_TYPE_P(op2) == IS_CONSTANT_AST)
+								&& !(GC_FLAGS(Z_AST_P(op2)) & IS_AST_DYNAMIC)) {
 							ZVAL_COPY_OR_DUP(&op2_tmp, op2);
 							zval_update_constant_ex(&op2_tmp, ce);
 							op2 = &op2_tmp;