Add compile-time restrictions on #[\NoDiscard] usage

Author: TimWolla

Zend/tests/attributes/nodiscard/unsupported_clone.phpt

@@ -0,0 +1,16 @@
+--TEST--
+#[\NoDiscard]: Not allowed on '__clone'.
+--FILE--
+<?php
+
+class Clazz {
+	#[\NoDiscard]
+	public function __clone() {
+	}
+}
+
+$cls = new Clazz();
+
+?>
+--EXPECTF--
+Fatal error: Method Clazz::__clone cannot be #[\NoDiscard] in %s on line %d

Zend/tests/attributes/nodiscard/unsupported_constructor.phpt

@@ -0,0 +1,16 @@
+--TEST--
+#[\NoDiscard]: Not allowed on '__construct'.
+--FILE--
+<?php
+
+class Clazz {
+	#[\NoDiscard]
+	public function __construct() {
+	}
+}
+
+$cls = new Clazz();
+
+?>
+--EXPECTF--
+Fatal error: Method Clazz::__construct cannot be #[\NoDiscard] in %s on line %d

Zend/tests/attributes/nodiscard/unsupported_never_function.phpt

@@ -0,0 +1,15 @@
+--TEST--
+#[\NoDiscard]: Not allowed on never function.
+--FILE--
+<?php
+
+#[\NoDiscard]
+function test(): never {
+	throw new \Exception('Error!');
+}
+
+test();
+
+?>
+--EXPECTF--
+Fatal error: A never returning function does not return a value, but #[\NoDiscard] requires a return value in %s on line %d

Zend/tests/attributes/nodiscard/unsupported_property_hook_get.phpt

@@ -0,0 +1,20 @@
+--TEST--
+#[\NoDiscard]: Not allowed on 'get' property hook.
+--FILE--
+<?php
+
+class Clazz {
+	public string $test {
+		#[\NoDiscard]
+		get {
+			return 'asd';
+		}
+	}
+}
+
+$cls = new Clazz();
+$cls->test;
+
+?>
+--EXPECTF--
+Fatal error: #[\NoDiscard] is not supported for property hooks in %s on line %d

Zend/tests/attributes/nodiscard/unsupported_property_hook_set.phpt

@@ -0,0 +1,20 @@
+--TEST--
+#[\NoDiscard]: Not allowed on 'set' property hook.
+--FILE--
+<?php
+
+class Clazz {
+	public string $test {
+		#[\NoDiscard]
+		set(string $value) {
+			$this->test = $value;
+		}
+	}
+}
+
+$cls = new Foo();
+$cls->test = 'foo';
+
+?>
+--EXPECTF--
+Fatal error: #[\NoDiscard] is not supported for property hooks in %s on line %d

Zend/tests/attributes/nodiscard/unsupported_void_function.phpt

@@ -0,0 +1,15 @@
+--TEST--
+#[\NoDiscard]: Not allowed on void function.
+--FILE--
+<?php
+
+#[\NoDiscard]
+function test(): void {
+	return;
+}
+
+test();
+
+?>
+--EXPECTF--
+Fatal error: A void function does not return a value, but #[\NoDiscard] requires a return value in %s on line %d

Zend/zend_API.c

@@ -2694,6 +2694,12 @@ static void zend_check_magic_method_arg_type(uint32_t arg_num, const zend_class_
 
 static void zend_check_magic_method_return_type(const zend_class_entry *ce, const zend_function *fptr, int error_type, int return_type)
 {
+	if (return_type == MAY_BE_VOID) {
+		if (fptr->common.fn_flags & ZEND_ACC_NODISCARD) {
+			zend_error_noreturn(error_type, "Method %s::%s cannot be #[\\NoDiscard]", ZSTR_VAL(ce->name), ZSTR_VAL(fptr->common.function_name));
+		}
+	}
+
 	if (!(fptr->common.fn_flags & ZEND_ACC_HAS_RETURN_TYPE)) {
 		/* For backwards compatibility reasons, do not enforce the return type if it is not set. */
 		return;
@@ -2753,6 +2759,10 @@ static void zend_check_magic_method_no_return_type(
 		zend_error_noreturn(error_type, "Method %s::%s() cannot declare a return type",
 			ZSTR_VAL(ce->name), ZSTR_VAL(fptr->common.function_name));
 	}
+
+	if (fptr->common.fn_flags & ZEND_ACC_NODISCARD) {
+		zend_error_noreturn(error_type, "Method %s::%s cannot be #[\\NoDiscard]", ZSTR_VAL(ce->name), ZSTR_VAL(fptr->common.function_name));
+	}
 }
 
 ZEND_API void zend_check_magic_method_implementation(const zend_class_entry *ce, const zend_function *fptr, zend_string *lcname, int error_type) /* {{{ */

Zend/zend_compile.c

@@ -8412,6 +8412,25 @@ static zend_op_array *zend_compile_func_decl_ex(
 	);
 
 	if (nodiscard_attribute) {
+		if (is_hook) {
+			zend_error_noreturn(E_COMPILE_ERROR, "#[\\NoDiscard] is not supported for property hooks");
+		}
+
+		if (op_array->fn_flags & ZEND_ACC_HAS_RETURN_TYPE) {
+			zend_arg_info *return_info = CG(active_op_array)->arg_info - 1;
+			if (ZEND_TYPE_CONTAINS_CODE(return_info->type, IS_VOID)) {
+				zend_error_noreturn(E_COMPILE_ERROR,
+					"A void %s does not return a value, but #[\\NoDiscard] requires a return value",
+					CG(active_class_entry) != NULL ? "method" : "function");
+			}
+
+			if (ZEND_TYPE_CONTAINS_CODE(return_info->type, IS_NEVER)) {
+				zend_error_noreturn(E_COMPILE_ERROR,
+					"A never returning %s does not return a value, but #[\\NoDiscard] requires a return value",
+					CG(active_class_entry) != NULL ? "method" : "function");
+			}
+		}
+
 		op_array->fn_flags |= ZEND_ACC_NODISCARD;
 	}