Forbid default values after all

I changed my mind...

Author: nikic

Zend/tests/readonly_props/readonly_with_default.phpt

@@ -15,5 +15,5 @@ try {
 }
 
 ?>
---EXPECT--
-Cannot modify readonly property Test::$prop
+--EXPECTF--
+Fatal error: Readonly property Test::$prop cannot have default value in %s on line %d

Zend/tests/readonly_props/serialization.phpt

@@ -4,7 +4,9 @@ Serialization of readonly properties
 <?php
 
 class Test {
-    public readonly int $prop = 1;
+    public function __construct(
+        public readonly int $prop = 1,
+    ) {}
 }
 
 var_dump($s = serialize(new Test));

Zend/zend_compile.c

@@ -7361,6 +7361,11 @@ void zend_compile_prop_decl(zend_ast *ast, zend_ast *type_ast, uint32_t flags, z
 				zend_error_noreturn(E_COMPILE_ERROR, "Readonly property %s::$%s must have type",
 					ZSTR_VAL(ce->name), ZSTR_VAL(name));
 			}
+			if (!Z_ISUNDEF(value_zv)) {
+				zend_error_noreturn(E_COMPILE_ERROR,
+					"Readonly property %s::$%s cannot have default value",
+					ZSTR_VAL(ce->name), ZSTR_VAL(name));
+			}
 			if (flags & ZEND_ACC_STATIC) {
 				zend_error_noreturn(E_COMPILE_ERROR,
 					"Static property %s::$%s cannot be readonly",