[RFC] Implement block expressions

Zend/tests/block_expr/001.phpt

@@ -0,0 +1,22 @@
+--TEST--
+Test basic basic block expression
+--FILE--
+<?php
+
+print {
+    echo "a\n";
+    echo "b\n";
+    "c\n"
+};
+
+print { "d\n" };
+
+print 'e' . { 'f' };
+
+?>
+--EXPECT--
+a
+b
+c
+d
+ef

Zend/tests/block_expr/002.phpt

@@ -0,0 +1,43 @@
+--TEST--
+Test block expression in arrow functions
+--FILE--
+<?php
+
+$a = 'a';
+
+var_dump((fn() => {
+    var_dump('b');
+    var_dump('c');
+    $a
+})());
+
+var_dump((fn() => {
+    var_dump('d');
+    var_dump('e');
+    return 'f';
+})());
+
+var_dump((fn() => {
+    var_dump('g');
+    var_dump('h');
+})());
+
+var_dump((fn() => {})());
+
+var_dump((fn() => {
+    'i'
+})());
+
+?>
+--EXPECT--
+string(1) "b"
+string(1) "c"
+string(1) "a"
+string(1) "d"
+string(1) "e"
+string(1) "f"
+string(1) "g"
+string(1) "h"
+NULL
+NULL
+string(1) "i"

Zend/tests/block_expr/003.phpt

@@ -0,0 +1,45 @@
+--TEST--
+Test block expression pretty printing
+--FILE--
+<?php
+
+assert((function () {
+    return {
+        echo 'Foo' . PHP_EOL;
+        {
+            echo 'Bar' . PHP_EOL;
+        }
+        false
+    };
+})());
+
+assert(10 + {
+    echo 'Foo';
+    -10
+});
+
+assert({ false });
+
+?>
+--EXPECTF--
+Foo
+Bar
+
+Warning: assert(): assert(function () {
+    return {
+        echo 'Foo' . PHP_EOL;
+        {
+            echo 'Bar' . PHP_EOL;
+        }
+        false
+    };
+}()) failed in %s on line %d
+Foo
+Warning: assert(): assert(10 + {
+    echo 'Foo';
+    -10
+}) failed in %s on line %d
+
+Warning: assert(): assert({
+    false
+}) failed in %s on line %d

Zend/tests/block_expr/004.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Test block expression compilation error when expression is missing
+--FILE--
+<?php
+
+$a = {};
+
+?>
+--EXPECTF--
+Fatal error: Block expression must return a value if its result is used in %s on line %d

Zend/tests/block_expr/005.phpt

@@ -0,0 +1,26 @@
+--TEST--
+Test exceptions in block expression
+--SKIPIF--
+<?php
+die("skip this test because it leaks memory");
+?>
+--FILE--
+<?php
+
+try {
+    $ary = [];
+    ($ary + [1]) + { throw new Exception('a'); null };
+} catch (Throwable $e) {
+    var_dump($e->getMessage());
+}
+
+try {
+    throw new Exception({ throw new Exception('b'); null });
+} catch (Throwable $e) {
+    var_dump($e->getMessage());
+}
+
+?>
+--EXPECT--
+string(1) "a"
+string(1) "b"

Zend/zend_ast.c

@@ -1193,6 +1193,7 @@ static ZEND_COLD void zend_ast_export_stmt(smart_str *str, zend_ast *ast, int in
 			case ZEND_AST_USE_TRAIT:
 			case ZEND_AST_NAMESPACE:
 			case ZEND_AST_DECLARE:
+			case ZEND_AST_BLOCK_EXPR:
 				break;
 			default:
 				smart_str_appendc(str, ';');
@@ -1501,6 +1502,17 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 		case ZEND_AST_TRAIT_ADAPTATIONS:
 			zend_ast_export_stmt(str, ast, indent);
 			break;
+		case ZEND_AST_BLOCK_EXPR:
+			smart_str_appends(str, "{\n");
+			zend_ast_export_stmt(str, ast->child[0], indent + 1);
+			if (ast->child[1] != NULL) {
+				zend_ast_export_indent(str, indent + 1);
+				zend_ast_export_ex(str, ast->child[1], 0, indent + 1);
+				smart_str_appendc(str, '\n');
+			}
+			zend_ast_export_indent(str, indent);
+			smart_str_appendc(str, '}');
+			break;
 		case ZEND_AST_IF:
 			zend_ast_export_if_stmt(str, (zend_ast_list*)ast, indent);
 			break;

Zend/zend_ast.h

@@ -123,6 +123,7 @@ enum _zend_ast_kind {
 	ZEND_AST_YIELD,
 	ZEND_AST_COALESCE,
 	ZEND_AST_ASSIGN_COALESCE,
+	ZEND_AST_BLOCK_EXPR,
 
 	ZEND_AST_STATIC,
 	ZEND_AST_WHILE,

Zend/zend_compile.c

@@ -4506,6 +4506,13 @@ void zend_compile_return(zend_ast *ast) /* {{{ */
 	if (!expr_ast) {
 		expr_node.op_type = IS_CONST;
 		ZVAL_NULL(&expr_node.u.constant);
+	} else if (expr_ast->kind == ZEND_AST_BLOCK_EXPR && expr_ast->child[1] == NULL) {
+		expr_node.op_type = IS_CONST;
+		ZVAL_NULL(&expr_node.u.constant);
+
+		znode result;
+		zend_compile_expr(&result, expr_ast);
+		zend_do_free(&result);
 	} else if (by_ref && zend_is_variable(expr_ast)) {
 		zend_compile_var(&expr_node, expr_ast, BP_VAR_W, 1);
 	} else {
@@ -8332,6 +8339,27 @@ void zend_compile_class_name(znode *result, zend_ast *ast) /* {{{ */
 }
 /* }}} */
 
+void zend_compile_block_expr(znode *result, zend_ast *ast) /* {{{ */
+{
+	zend_bool result_unused = (ast->attr & ZEND_BLOCK_EXPR_RESULT_UNUSED) != 0;
+	zend_ast *statement_list = ast->child[0];
+	zend_ast *expr_ast = ast->child[1];
+
+	zend_compile_stmt(statement_list);
+
+	if (expr_ast != NULL) {
+		zend_compile_expr(result, expr_ast);
+	} else {
+		if (!result_unused) {
+			zend_error_noreturn(E_COMPILE_ERROR, "Block expression must return a value if its result is used");
+		}
+
+		ZVAL_NULL(&result->u.constant);
+		result->op_type = IS_CONST;
+	}
+}
+/* }}} */
+
 static zend_op *zend_compile_rope_add_ex(zend_op *opline, znode *result, uint32_t num, znode *elem_node) /* {{{ */
 {
 	if (num == 0) {
@@ -8952,6 +8980,9 @@ void zend_compile_expr(znode *result, zend_ast *ast) /* {{{ */
 		case ZEND_AST_ARROW_FUNC:
 			zend_compile_func_decl(result, ast, 0);
 			return;
+		case ZEND_AST_BLOCK_EXPR:
+			zend_compile_block_expr(result, ast);
+			return;
 		default:
 			ZEND_ASSERT(0 /* not supported */);
 	}

Zend/zend_compile.h

@@ -1009,6 +1009,9 @@ static zend_always_inline int zend_check_arg_send_type(const zend_function *zf,
 /* Attribute for ternary inside parentheses */
 #define ZEND_PARENTHESIZED_CONDITIONAL 1
 
+/* Attribute for block expression at statement level */
+#define ZEND_BLOCK_EXPR_RESULT_UNUSED 1
+
 /* For "use" AST nodes and the seen symbol table */
 #define ZEND_SYMBOL_CLASS    (1<<0)
 #define ZEND_SYMBOL_FUNCTION (1<<1)