Proposal: Make match expression a constant expression (when parts are constant)

Zend/tests/match/043.phpt

@@ -0,0 +1,47 @@
+--TEST--
+Match expression can be used as a constant expression
+--FILE--
+<?php
+
+// Here, this test uses strtolower because the locale dependence and change to the string
+// ensures PHP has to use a temporary value instead of a literal, to test memory management.
+//
+// It's already possible to throw from a constant expression (e.g. undeclared constants),
+// and match() can be seen as a much shorter way than changed ternary conditions on the same constant expressions.
+define('dynamic_value', strtolower('FOO'));
+function my_test($invalid = match(dynamic_value) {}) {
+    return $invalid;
+}
+
+const X = match (dynamic_value) {
+    default => 123,
+};
+echo "X=",X,"\n";
+const Y = match (dynamic_value) {
+    'a', 'b' => 'default',
+    default => dynamic_value . 'd',
+};
+echo "Y=",Y,"\n";
+const Z = match (dynamic_value) {
+    'a', 'foo', 'b' => [dynamic_value],
+    default => dynamic_value,
+};
+echo "Z=",json_encode(Z),"\n";
+
+echo json_encode(my_test([dynamic_value])), "\n";
+for ($i = 0; $i < 2; $i++) {
+    try {
+        my_test();
+    } catch (UnhandledMatchError $e) {
+        echo "Caught {$e->getMessage()} at line {$e->getLine()}\n";
+    }
+}
+
+?>
+--EXPECT--
+X=123
+Y=food
+Z=["foo"]
+["foo"]
+Caught Unhandled match value of type string at line 9
+Caught Unhandled match value of type string at line 9

Zend/tests/match/044.phpt

@@ -0,0 +1,12 @@
+--TEST--
+Match expression can be used as a constant expression unless parts aren't constant
+--FILE--
+<?php
+
+// This is an uncatchable fatal error caused by compiling this file.
+const X = match ($x) {
+    default => 123,
+};
+?>
+--EXPECTF--
+Fatal error: Constant expression contains invalid operations in %s044.php on line 4

Zend/zend_ast.c

@@ -654,6 +654,51 @@ ZEND_API int ZEND_FASTCALL zend_ast_evaluate(zval *result, zend_ast *ast, zend_c
 				zval_ptr_dtor_nogc(&op1);
 			}
 			break;
+		case ZEND_AST_MATCH:
+		{
+			zend_ast_list *list;
+			uint32_t i;
+			if (UNEXPECTED(zend_ast_evaluate(&op1, ast->child[0], scope) != SUCCESS)) {
+				ret = FAILURE;
+				break;
+			}
+			list = zend_ast_get_list(ast->child[1]);
+			for (i = 0; i < list->children; i++) {
+				zend_ast *arm = list->child[i];
+				zend_ast_list *arm_expr_list;
+				uint32_t j;
+				if (arm->child[0] == NULL) {
+return_arm_expr:
+					if (UNEXPECTED(zend_ast_evaluate(result, arm->child[1], scope) != SUCCESS)) {
+						zval_ptr_dtor_nogc(&op1);
+						return FAILURE;
+					}
+					zval_ptr_dtor_nogc(&op1);
+					return SUCCESS;
+				}
+				arm_expr_list = zend_ast_get_list(arm->child[0]);
+				for (j = 0; j < arm_expr_list->children; j++) {
+					zval is_identical_zv;
+					if (UNEXPECTED(zend_ast_evaluate(&op2, arm_expr_list->child[j], scope) != SUCCESS)) {
+						return FAILURE;
+					}
+					ret = is_identical_function(&is_identical_zv, &op1, &op2);
+					zval_ptr_dtor_nogc(&op2);
+					if (ret != SUCCESS) {
+						zval_ptr_dtor_nogc(&op1);
+						return ret;
+					}
+					if (Z_TYPE(is_identical_zv) == IS_TRUE) {
+						goto return_arm_expr;
+					}
+				}
+			}
+
+			zend_throw_exception_ex(zend_ce_unhandled_match_error, 0, "Unhandled match value of type %s", zend_zval_type_name(&op1));
+			zval_ptr_dtor_nogc(&op1);
+			ret = FAILURE;
+			break;
+		}
 		case ZEND_AST_COALESCE:
 			if (UNEXPECTED(zend_ast_evaluate(&op1, ast->child[0], scope) != SUCCESS)) {
 				ret = FAILURE;

Zend/zend_compile.c

@@ -9144,7 +9144,9 @@ zend_bool zend_is_allowed_in_const_expr(zend_ast_kind kind) /* {{{ */
 		|| kind == ZEND_AST_UNPACK
 		|| kind == ZEND_AST_CONST || kind == ZEND_AST_CLASS_CONST
 		|| kind == ZEND_AST_CLASS_NAME
-		|| kind == ZEND_AST_MAGIC_CONST || kind == ZEND_AST_COALESCE;
+		|| kind == ZEND_AST_MAGIC_CONST || kind == ZEND_AST_COALESCE
+		|| kind == ZEND_AST_MATCH || kind == ZEND_AST_MATCH_ARM
+		|| kind == ZEND_AST_MATCH_ARM_LIST || kind == ZEND_AST_EXPR_LIST;
 }
 /* }}} */