Reapply GH-17712 with a fix for internal class constants

Add recursion protection when emitting deprecation warnings for class
constants, since the deprecation message can come from an attribute that is
using the same constant for the message, or otherwise result in recursion.

But, internal constants are persisted, and thus cannot have recursion
protection. Otherwise, if a user error handler triggers bailout before the
recursion flag is removed then a subsequent request (e.g. with `--repeat 2`)
would start with that flag already applied. Internal constants can presumably
be trusted not to use deprecation messages that come from recursive attributes.

Fixes GH-18463
Fixes GH-17711

Author: DanielEScherzer

NEWS

@@ -2,6 +2,11 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.4.8
 
+- Core:
+  . Fixed bugs GH-17711 and GH-18022 (Infinite recursion on deprecated attribute
+    evaluation) and GH-18464 (Recursion protection for deprecation constants not
+    released on bailout). (DanielEScherzer and ilutov)
+
 - Date:
   . Fixed bug GH-18076 (Since PHP 8, the date_sun_info() function returns
     inaccurate sunrise and sunset times, but other calculated times are
@@ -35,8 +40,6 @@ PHP                                                                        NEWS
 24 Apr 2025, PHP 8.4.7
 
 - Core:
-  . Fixed bug GH-17711 and GH-18022 (Infinite recursion on deprecated attribute
-    evaluation). (ilutov)
   . Fixed bug GH-18038 (Lazy proxy calls magic methods twice). (Arnaud)
   . Fixed bug GH-18209 (Use-after-free in extract() with EXTR_REFS). (ilutov)
   . Fixed bug GH-18268 (Segfault in array_walk() on object with added property

Zend/tests/attributes/deprecated/class_constants/gh17711.phpt

@@ -0,0 +1,28 @@
+--TEST--
+GH-17711: Infinite recursion through deprecated class constants self-referencing through deprecation message
+--FILE--
+<?php
+
+class C {
+    #[\Deprecated(self::C)]
+    const C = TEST;
+}
+
+const TEST = 'Message';
+var_dump(C::C);
+
+class D {
+    #[\Deprecated(Alias::C)]
+    const C = 'test';
+}
+
+class_alias('D', 'Alias');
+var_dump(D::C);
+
+?>
+--EXPECTF--
+Deprecated: Constant C::C is deprecated, Message in %s on line %d
+string(7) "Message"
+
+Deprecated: Constant D::C is deprecated, test in %s on line %d
+string(4) "test"

Zend/tests/constants/gh18463-class-constant.phpt

@@ -0,0 +1,20 @@
+--TEST--
+GH-18463: Recursion protection should not be applied to internal class constants
+--EXTENSIONS--
+zend_test
+--FILE--
+<?php
+
+function handler($errno, $errstr, $errfile, $errline) {
+	echo "$errstr in $errfile on line $errline\n";
+	eval('class string {}');
+}
+
+set_error_handler('handler');
+
+var_dump(_ZendTestClass::ZEND_TEST_DEPRECATED);
+?>
+--EXPECTF--
+Constant _ZendTestClass::ZEND_TEST_DEPRECATED is deprecated in %s on line %d
+
+Fatal error: Cannot use "string" as a class name as it is reserved in %s(%d) : eval()'d code on line %d

Zend/zend_API.c

@@ -1439,7 +1439,7 @@ ZEND_API HashTable *zend_separate_class_constants_table(zend_class_entry *class_
 
 	ZEND_HASH_MAP_FOREACH_STR_KEY_PTR(&class_type->constants_table, key, c) {
 		if (c->ce == class_type) {
-			if (Z_TYPE(c->value) == IS_CONSTANT_AST) {
+			if (Z_TYPE(c->value) == IS_CONSTANT_AST || (ZEND_CLASS_CONST_FLAGS(c) & ZEND_ACC_DEPRECATED)) {
 				new_c = zend_arena_alloc(&CG(arena), sizeof(zend_class_constant));
 				memcpy(new_c, c, sizeof(zend_class_constant));
 				c = new_c;

Zend/zend_compile.c

@@ -8822,6 +8822,10 @@ static void zend_compile_class_const_decl(zend_ast *ast, uint32_t flags, zend_as
 
 			if (deprecated) {
 				ZEND_CLASS_CONST_FLAGS(c) |= ZEND_ACC_DEPRECATED;
+				/* For deprecated constants, we need to flag the zval for recursion
+				 * detection. Make sure the zval is separated out of shm. */
+				ce->ce_flags |= ZEND_ACC_HAS_AST_CONSTANTS;
+				ce->ce_flags &= ~ZEND_ACC_CONSTANTS_UPDATED;
 			}
 		}
 	}

Zend/zend_constants.c

@@ -353,8 +353,15 @@ ZEND_API zval *zend_get_class_constant_ex(zend_string *class_name, zend_string *
 			}
 
 			if (UNEXPECTED(ZEND_CLASS_CONST_FLAGS(c) & ZEND_ACC_DEPRECATED)) {
-				if ((flags & ZEND_FETCH_CLASS_SILENT) == 0) {
+				if ((flags & ZEND_FETCH_CLASS_SILENT) == 0 && !CONST_IS_RECURSIVE(c)) {
+					if (c->ce->type == ZEND_USER_CLASS) {
+						/* Recursion protection only applied to user constants, GH-18463 */
+						CONST_PROTECT_RECURSION(c);
+					}
 					zend_deprecated_class_constant(c, constant_name);
+					if (c->ce->type == ZEND_USER_CLASS) {
+						CONST_UNPROTECT_RECURSION(c);
+					}
 					if (EG(exception)) {
 						goto failure;
 					}

Zend/zend_constants.h

@@ -27,6 +27,17 @@
 #define CONST_NO_FILE_CACHE		(1<<1)				/* Can't be saved in file cache */
 #define CONST_DEPRECATED		(1<<2)				/* Deprecated */
 #define CONST_OWNED				(1<<3)				/* constant should be destroyed together with class */
+#define CONST_RECURSIVE			(1<<4)				/* Recursion protection for constant evaluation */
+
+#define CONST_IS_RECURSIVE(c) (Z_CONSTANT_FLAGS((c)->value) & CONST_RECURSIVE)
+#define CONST_PROTECT_RECURSION(c) \
+	do { \
+		Z_CONSTANT_FLAGS((c)->value) |= CONST_RECURSIVE; \
+	} while (0)
+#define CONST_UNPROTECT_RECURSION(c) \
+	do { \
+		Z_CONSTANT_FLAGS((c)->value) &= ~CONST_RECURSIVE; \
+	} while (0)
 
 #define	PHP_USER_CONSTANT   0x7fffff /* a constant defined in user space */
 

Zend/zend_vm_def.h

@@ -6094,8 +6094,15 @@ ZEND_VM_HANDLER(181, ZEND_FETCH_CLASS_CONSTANT, VAR|CONST|UNUSED|CLASS_FETCH, CO
 			}
 
 			bool is_constant_deprecated = ZEND_CLASS_CONST_FLAGS(c) & ZEND_ACC_DEPRECATED;
-			if (UNEXPECTED(is_constant_deprecated)) {
+			if (UNEXPECTED(is_constant_deprecated) && !CONST_IS_RECURSIVE(c)) {			
+				if (c->ce->type == ZEND_USER_CLASS) {
+					/* Recursion protection only applied to user constants, GH-18463 */
+					CONST_PROTECT_RECURSION(c);
+				}
 				zend_deprecated_class_constant(c, constant_name);
+				if (c->ce->type == ZEND_USER_CLASS) {
+					CONST_UNPROTECT_RECURSION(c);
+				}
 
 				if (EG(exception)) {
 					ZVAL_UNDEF(EX_VAR(opline->result.var));

Zend/zend_vm_execute.h

@@ -3800,6 +3800,11 @@ static bool preload_try_resolve_constants(zend_class_entry *ce)
 		ZEND_HASH_MAP_FOREACH_STR_KEY_PTR(&ce->constants_table, key, c) {
 			val = &c->value;
 			if (Z_TYPE_P(val) == IS_CONSTANT_AST) {
+				/* For deprecated constants, we need to flag the zval for recursion
+				 * detection. Make sure the zval is separated out of shm. */
+				if (ZEND_CLASS_CONST_FLAGS(c) & ZEND_ACC_DEPRECATED) {
+					ok = false;
+				}
 				if (EXPECTED(zend_update_class_constant(c, key, c->ce) == SUCCESS)) {
 					was_changed = changed = true;
 				} else {