Implement GH-18261: Allow cast to be used in constant expressions

Author: ndossche

UPGRADING

@@ -130,6 +130,7 @@ PHP 8.5 UPGRADE NOTES
     RFC: https://wiki.php.net/rfc/marking_return_value_as_important
   . Added asymmetric visibility support for static properties.
     RFC: https://wiki.php.net/rfc/static-aviz
+  . It is now possible to use casts in constant expressions.
 
 - Curl:
   . Added support for share handles that are persisted across multiple PHP

Zend/tests/constexpr/constant_expressions_cast.phpt

@@ -0,0 +1,51 @@
+--TEST--
+Constant expressions with cast
+--FILE--
+<?php
+class X {
+    public int $foo = 3;
+}
+
+const T1 = (int) 0.3;
+const T2 = (bool) 0.3;
+const T3 = (string) [];
+const T4 = (object) ["a" => 1];
+const T5 = (float) 5;
+const T6 = (array) "";
+const T7 = (array) var_dump(...);
+const T8 = (array) new X;
+
+var_dump(T1, T2, T3, T4, T5, T6, T7, T8);
+?>
+--EXPECTF--
+Warning: Array to string conversion in %s on line %d
+int(0)
+bool(true)
+string(5) "Array"
+object(stdClass)#%d (1) {
+  ["a"]=>
+  int(1)
+}
+float(5)
+array(1) {
+  [0]=>
+  string(0) ""
+}
+array(1) {
+  [0]=>
+  object(Closure)#%d (2) {
+    ["function"]=>
+    string(8) "var_dump"
+    ["parameter"]=>
+    array(2) {
+      ["$value"]=>
+      string(10) "<required>"
+      ["$values"]=>
+      string(10) "<optional>"
+    }
+  }
+}
+array(1) {
+  ["foo"]=>
+  int(3)
+}

Zend/zend_ast.c

@@ -702,6 +702,71 @@ ZEND_API zend_result ZEND_FASTCALL zend_ast_evaluate_inner(
 			}
 			zval_ptr_dtor_nogc(&op1);
 			break;
+		case ZEND_AST_CAST:
+			if (UNEXPECTED(zend_ast_evaluate_ex(&op1, ast->child[0], scope, &short_circuited, ctx) != SUCCESS)) {
+				ret = FAILURE;
+				break;
+			}
+			if (ast->attr == Z_TYPE(op1)) {
+				ZVAL_COPY_VALUE(result, &op1);
+			} else {
+				switch (ast->attr) {
+					case _IS_BOOL:
+						ZVAL_BOOL(result, zend_is_true(&op1));
+						zval_ptr_dtor_nogc(&op1);
+						break;
+					case IS_LONG:
+						ZVAL_LONG(result, zval_get_long_func(&op1, false));
+						zval_ptr_dtor_nogc(&op1);
+						break;
+					case IS_DOUBLE:
+						ZVAL_DOUBLE(result, zval_get_double_func(&op1));
+						zval_ptr_dtor_nogc(&op1);
+						break;
+					case IS_STRING:
+						ZVAL_STR(result, zval_get_string_func(&op1));
+						zval_ptr_dtor_nogc(&op1);
+						break;
+					case IS_ARRAY:
+						/* Adapted from VM */
+						if (Z_TYPE(op1) != IS_OBJECT || Z_OBJCE(op1) == zend_ce_closure) {
+							if (Z_TYPE(op1) != IS_NULL) {
+								ZVAL_ARR(result, zend_new_array(1));
+								zend_hash_index_add_new(Z_ARRVAL_P(result), 0, &op1);
+							} else {
+								ZVAL_EMPTY_ARRAY(result);
+							}
+						} else {
+							/* Constant AST only allows building stdClass objects, closures, or user classes;
+							 * all of which should be compatible. */
+							ZEND_ASSERT(ZEND_STD_BUILD_OBJECT_PROPERTIES_ARRAY_COMPATIBLE(&op1));
+
+							/* Optimized version without rebuilding properties HashTable */
+							ZVAL_ARR(result, zend_std_build_object_properties_array(Z_OBJ(op1)));
+							zval_ptr_dtor_nogc(&op1);
+						}
+						break;
+					case IS_OBJECT:
+						/* Adapted from VM */
+						ZVAL_OBJ(result, zend_objects_new(zend_standard_class_def));
+						if (Z_TYPE(op1) == IS_ARRAY) {
+							HashTable *ht = zend_symtable_to_proptable(Z_ARR(op1));
+							if (GC_FLAGS(ht) & IS_ARRAY_IMMUTABLE) {
+								/* TODO: try not to duplicate immutable arrays as well ??? */
+								ht = zend_array_dup(ht);
+							}
+							Z_OBJ_P(result)->properties = ht;
+							zval_ptr_dtor_nogc(&op1);
+						} else if (Z_TYPE(op1) != IS_NULL) {
+							HashTable *ht = zend_new_array(1);
+							Z_OBJ_P(result)->properties = ht;
+							zend_hash_add_new(ht, ZSTR_KNOWN(ZEND_STR_SCALAR), &op1);
+						}
+						break;
+					EMPTY_SWITCH_DEFAULT_CASE();
+				}
+			}
+			break;
 		case ZEND_AST_OR:
 			if (UNEXPECTED(zend_ast_evaluate_ex(&op1, ast->child[0], scope, &short_circuited, ctx) != SUCCESS)) {
 				ret = FAILURE;

Zend/zend_compile.c

@@ -11156,6 +11156,7 @@ static bool zend_is_allowed_in_const_expr(zend_ast_kind kind) /* {{{ */
 		|| kind == ZEND_AST_AND || kind == ZEND_AST_OR
 		|| kind == ZEND_AST_UNARY_OP
 		|| kind == ZEND_AST_UNARY_PLUS || kind == ZEND_AST_UNARY_MINUS
+		|| kind == ZEND_AST_CAST
 		|| kind == ZEND_AST_CONDITIONAL || kind == ZEND_AST_DIM
 		|| kind == ZEND_AST_ARRAY || kind == ZEND_AST_ARRAY_ELEM
 		|| kind == ZEND_AST_UNPACK