GH-19153: Validate #[\Attribute] targets (#19154)

Do not allow #[\Attribute] on traits, interfaces, enums, or abstract classes.

Author: DanielEScherzer

NEWS

@@ -62,6 +62,8 @@ PHP                                                                        NEWS
   . The socket_set_timeout() alias function has been deprecated. (timwolla)
   . Passing null to to readdir(), rewinddir(), and closedir() to use the last
     opened directory has been deprecated. (Girgias)
+  . Fixed bug GH-19153 (#[\Attribute] validation should error on
+    trait/interface/enum/abstract class). (DanielEScherzer)
 
 31 Jul 2025, PHP 8.5.0alpha4
 

Zend/tests/attributes/Attribute/Attribute_on_abstract.phpt

@@ -0,0 +1,12 @@
+--TEST--
+#[Attribute] on an abstract class
+--FILE--
+<?php
+
+#[Attribute]
+abstract class Demo {}
+
+echo "Done\n";
+?>
+--EXPECTF--
+Fatal error: Cannot apply #[\Attribute] to abstract class Demo in %s on line %d

Zend/tests/attributes/Attribute/Attribute_on_enum.phpt

@@ -0,0 +1,12 @@
+--TEST--
+#[Attribute] on an enum
+--FILE--
+<?php
+
+#[Attribute]
+enum Demo {}
+
+echo "Done\n";
+?>
+--EXPECTF--
+Fatal error: Cannot apply #[\Attribute] to enum Demo in %s on line %d

Zend/tests/attributes/Attribute/Attribute_on_interface.phpt

@@ -0,0 +1,12 @@
+--TEST--
+#[Attribute] on an interface
+--FILE--
+<?php
+
+#[Attribute]
+interface Demo {}
+
+echo "Done\n";
+?>
+--EXPECTF--
+Fatal error: Cannot apply #[\Attribute] to interface Demo in %s on line %d

Zend/tests/attributes/Attribute/Attribute_on_trait.phpt

@@ -0,0 +1,12 @@
+--TEST--
+#[Attribute] on a trait
+--FILE--
+<?php
+
+#[Attribute]
+trait Demo {}
+
+echo "Done\n";
+?>
+--EXPECTF--
+Fatal error: Cannot apply #[\Attribute] to trait Demo in %s on line %d

Zend/zend_attributes.c

@@ -95,6 +95,24 @@ static void validate_allow_dynamic_properties(
 	scope->ce_flags |= ZEND_ACC_ALLOW_DYNAMIC_PROPERTIES;
 }
 
+static void validate_attribute(
+	zend_attribute *attr, uint32_t target, zend_class_entry *scope)
+{
+	const char *msg = NULL;
+	if (scope->ce_flags & ZEND_ACC_TRAIT) {
+		msg = "Cannot apply #[\\Attribute] to trait %s";
+	} else if (scope->ce_flags & ZEND_ACC_INTERFACE) {
+		msg = "Cannot apply #[\\Attribute] to interface %s";
+	} else if (scope->ce_flags & ZEND_ACC_ENUM) {
+		msg = "Cannot apply #[\\Attribute] to enum %s";
+	} else if (scope->ce_flags & ZEND_ACC_EXPLICIT_ABSTRACT_CLASS) {
+		msg = "Cannot apply #[\\Attribute] to abstract class %s";
+	}
+	if (msg != NULL) {
+		zend_error_noreturn(E_ERROR, msg, ZSTR_VAL(scope->name));
+	}
+}
+
 ZEND_METHOD(Attribute, __construct)
 {
 	zend_long flags = ZEND_ATTRIBUTE_TARGET_ALL;
@@ -522,6 +540,7 @@ void zend_register_attribute_ce(void)
 
 	zend_ce_attribute = register_class_Attribute();
 	attr = zend_mark_internal_attribute(zend_ce_attribute);
+	attr->validator = validate_attribute;
 
 	zend_ce_return_type_will_change_attribute = register_class_ReturnTypeWillChange();
 	zend_mark_internal_attribute(zend_ce_return_type_will_change_attribute);