Add support for final class constants

RFC: https://wiki.php.net/rfc/final_class_const

Co-authored-by: Nikita Popov <nikita.ppv@gmail.com>

UPGRADING

@@ -67,6 +67,8 @@ PHP 8.1 UPGRADE NOTES
   . Added support for intersection types.
     They cannot be combined with union types.
     RFC: https://wiki.php.net/rfc/pure-intersection-types
+  . Added support for the final modifier for class constants.
+    RFC: https://wiki.php.net/rfc/final_class_const
 
 - Fileinfo:
   . The fileinfo functions now accept and return, respectively, finfo objects

Zend/tests/bug49472.phpt

@@ -23,5 +23,6 @@ class FooBar extends Foo implements ia {
 new FooBar;
 
 ?>
---EXPECTF--
-Fatal error: Cannot inherit previously-inherited or override constant c from interface ia in %s on line %d
+===DONE===
+--EXPECT--
+===DONE===

Zend/tests/constants/final_constants/final_const1.phpt

@@ -0,0 +1,13 @@
+--TEST--
+Class constants support the final modifier
+--FILE--
+<?php
+
+class Foo
+{
+    final const A = "foo";
+    final public const B = "foo";
+}
+
+?>
+--EXPECT--

Zend/tests/constants/final_constants/final_const10.phpt

@@ -0,0 +1,22 @@
+--TEST--
+Interface constants inherited from other interfaces can be redeclared
+--FILE--
+<?php
+
+interface I1
+{
+    const C = 1;
+}
+
+interface I2
+{
+    const C = 2;
+}
+
+interface I3 extends I1, I2
+{
+    const C = 3;
+}
+
+?>
+--EXPECT--

Zend/tests/constants/final_constants/final_const11.phpt

@@ -0,0 +1,22 @@
+--TEST--
+Class constants cannot be inherited from both a class and an interface
+--FILE--
+<?php
+
+class C
+{
+    const C = 1;
+}
+
+interface I
+{
+    const C = 1;
+}
+
+class C2 extends C implements I
+{
+}
+
+?>
+--EXPECTF--
+Fatal error: Class C2 inherits both C::C and I::C, which is ambiguous in %s on line %d

Zend/tests/constants/final_constants/final_const12.phpt

@@ -0,0 +1,22 @@
+--TEST--
+Interface constants cannot be inherited from other interfaces
+--FILE--
+<?php
+
+interface I1
+{
+    const C = 1;
+}
+
+interface I2
+{
+    const C = 2;
+}
+
+interface I3 extends I1, I2
+{
+}
+
+?>
+--EXPECTF--
+Fatal error: Class I3 inherits both I1::C and I2::C, which is ambiguous in %s on line %d

Zend/tests/constants/final_constants/final_const2.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Final class constants cannot be overridden
+--FILE--
+<?php
+
+class Foo
+{
+    final const A = "foo";
+}
+
+class Bar extends Foo
+{
+    const A = "bar";
+}
+
+?>
+--EXPECTF--
+Fatal error: Bar::A cannot override final constant Foo::A in %s on line %d

Zend/tests/constants/final_constants/final_const3.phpt

@@ -0,0 +1,13 @@
+--TEST--
+Private class constants cannot be final
+--FILE--
+<?php
+
+class Foo
+{
+    private final const A = "foo";
+}
+
+?>
+--EXPECTF--
+Fatal error: Private constant Foo::A cannot be final as it is not visible to other classes in %s on line %d

Zend/tests/constants/final_constants/final_const4.phpt

@@ -0,0 +1,17 @@
+--TEST--
+Interface constants can be overridden directly
+--FILE--
+<?php
+
+interface I
+{
+    const X = 1;
+}
+
+class C implements I
+{
+    const X = 2;
+}
+
+?>
+--EXPECT--

Zend/tests/constants/final_constants/final_const5.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Final interface constants cannot be overridden directly
+--FILE--
+<?php
+
+interface I
+{
+    final public const X = 1;
+}
+
+class C implements I
+{
+    const X = 2;
+}
+
+?>
+--EXPECTF--
+Fatal error: C::X cannot override final constant I::X in %s on line %d

Zend/tests/constants/final_constants/final_const6.phpt

@@ -0,0 +1,16 @@
+--TEST--
+Final interface constants can be inherited
+--FILE--
+<?php
+
+interface I
+{
+    final public const X = 1;
+}
+
+class C implements I
+{
+}
+
+?>
+--EXPECT--

Zend/tests/constants/final_constants/final_const7.phpt

@@ -0,0 +1,19 @@
+--TEST--
+Interface constants can be overridden indirectly
+--FILE--
+<?php
+
+interface I
+{
+    const X = 1;
+}
+
+class C implements I {}
+
+class D extends C
+{
+    const X = 2;
+}
+
+?>
+--EXPECT--

Zend/tests/constants/final_constants/final_const8.phpt

@@ -0,0 +1,22 @@
+--TEST--
+Class constants cannot be inherited from two different interfaces
+--FILE--
+<?php
+
+interface I1
+{
+    const C = 1;
+}
+
+interface I2
+{
+    const C = 1;
+}
+
+class C implements I1, I2
+{
+}
+
+?>
+--EXPECTF--
+Fatal error: Class C inherits both I1::C and I2::C, which is ambiguous in %s on line %d

Zend/tests/constants/final_constants/final_const9.phpt

@@ -0,0 +1,22 @@
+--TEST--
+Class constants inherited from interfaces can be redeclared
+--FILE--
+<?php
+
+interface I1
+{
+    const C = 1;
+}
+
+interface I2
+{
+    const C = 2;
+}
+
+class C implements I1, I2
+{
+    const C = 3;
+}
+
+?>
+--EXPECT--

Zend/tests/errmsg_025.phpt

@@ -17,4 +17,4 @@ class test implements test1, test2 {
 echo "Done\n";
 ?>
 --EXPECTF--
-Fatal error: Cannot inherit previously-inherited or override constant FOO from interface test2 in %s on line %d
+Fatal error: Class test inherits both test1::FOO and test2::FOO, which is ambiguous in %s on line %d

Zend/tests/errmsg_038.phpt

@@ -10,4 +10,4 @@ class test {
 echo "Done\n";
 ?>
 --EXPECTF--
-Fatal error: Cannot declare property test::$var final, the final modifier is allowed only for methods and classes in %s on line %d
+Fatal error: Cannot declare property test::$var final, the final modifier is allowed only for methods, classes, and class constants in %s on line %d

Zend/zend_API.c

@@ -4331,12 +4331,12 @@ ZEND_API void zend_declare_property_stringl(zend_class_entry *ce, const char *na
 }
 /* }}} */
 
-ZEND_API zend_class_constant *zend_declare_class_constant_ex(zend_class_entry *ce, zend_string *name, zval *value, int access_type, zend_string *doc_comment) /* {{{ */
+ZEND_API zend_class_constant *zend_declare_class_constant_ex(zend_class_entry *ce, zend_string *name, zval *value, int flags, zend_string *doc_comment) /* {{{ */
 {
 	zend_class_constant *c;
 
 	if (ce->ce_flags & ZEND_ACC_INTERFACE) {
-		if (access_type != ZEND_ACC_PUBLIC) {
+		if (!(flags & ZEND_ACC_PUBLIC)) {
 			zend_error_noreturn(E_COMPILE_ERROR, "Access type for interface constant %s::%s must be public", ZSTR_VAL(ce->name), ZSTR_VAL(name));
 		}
 	}
@@ -4356,7 +4356,7 @@ ZEND_API zend_class_constant *zend_declare_class_constant_ex(zend_class_entry *c
 		c = zend_arena_alloc(&CG(arena), sizeof(zend_class_constant));
 	}
 	ZVAL_COPY_VALUE(&c->value, value);
-	ZEND_CLASS_CONST_FLAGS(c) = access_type;
+	ZEND_CLASS_CONST_FLAGS(c) = flags;
 	c->doc_comment = doc_comment;
 	c->attributes = NULL;
 	c->ce = ce;

Zend/zend_compile.c

@@ -7270,7 +7270,7 @@ void zend_compile_prop_decl(zend_ast *ast, zend_ast *type_ast, uint32_t flags, z
 
 		if (flags & ZEND_ACC_FINAL) {
 			zend_error_noreturn(E_COMPILE_ERROR, "Cannot declare property %s::$%s final, "
-				"the final modifier is allowed only for methods and classes",
+				"the final modifier is allowed only for methods, classes, and class constants",
 				ZSTR_VAL(ce->name), ZSTR_VAL(name));
 		}
 
@@ -7358,10 +7358,17 @@ void zend_compile_class_const_decl(zend_ast *ast, uint32_t flags, zend_ast *attr
 		zend_string *doc_comment = doc_comment_ast ? zend_string_copy(zend_ast_get_str(doc_comment_ast)) : NULL;
 		zval value_zv;
 
-		if (UNEXPECTED(flags & (ZEND_ACC_STATIC|ZEND_ACC_ABSTRACT|ZEND_ACC_FINAL))) {
+		if (UNEXPECTED(flags & (ZEND_ACC_STATIC|ZEND_ACC_ABSTRACT))) {
 			zend_check_const_and_trait_alias_attr(flags, "constant");
 		}
 
+		if (UNEXPECTED((flags & ZEND_ACC_PRIVATE) && (flags & ZEND_ACC_FINAL))) {
+			zend_error_noreturn(
+				E_COMPILE_ERROR, "Private constant %s::%s cannot be final as it is not visible to other classes",
+				ZSTR_VAL(ce->name), ZSTR_VAL(name)
+			);
+		}
+
 		zend_const_expr_to_zval(&value_zv, value_ast_ptr);
 		c = zend_declare_class_constant_ex(ce, name, &value_zv, flags, doc_comment);