Deprecate unparenthesized concatenation and addition/subtraction

Zend/zend_ast.c

@@ -1682,6 +1682,7 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 				case ZEND_MOD:                 BINARY_OP(" % ",   210, 210, 211);
 				case ZEND_SL:                  BINARY_OP(" << ",  190, 190, 191);
 				case ZEND_SR:                  BINARY_OP(" >> ",  190, 190, 191);
+				case ZEND_PARENTHESIZED_CONCAT: /* fallthrough */
 				case ZEND_CONCAT:              BINARY_OP(" . ",   200, 200, 201);
 				case ZEND_BW_OR:               BINARY_OP(" | ",   140, 140, 141);
 				case ZEND_BW_AND:              BINARY_OP(" & ",   160, 160, 161);

Zend/zend_compile.c

@@ -6966,6 +6966,16 @@ void zend_compile_binary_op(znode *result, zend_ast *ast) /* {{{ */
 	zend_ast *right_ast = ast->child[1];
 	uint32_t opcode = ast->attr;
 
+	if ((opcode == ZEND_ADD || opcode == ZEND_SUB) && left_ast->kind == ZEND_AST_BINARY_OP && left_ast->attr == ZEND_CONCAT) {
+		zend_error(E_DEPRECATED, "The behavior of unparenthesized expressions containing both '.' and '+'/'-' will change in PHP 8: '+'/'-' will take a higher precedence");
+	}
+	if ((opcode == ZEND_SL || opcode == ZEND_SR) && ((left_ast->kind == ZEND_AST_BINARY_OP && left_ast->attr == ZEND_CONCAT) || (right_ast->kind == ZEND_AST_BINARY_OP && right_ast->attr == ZEND_CONCAT))) {
+		zend_error(E_DEPRECATED, "The behavior of unparenthesized expressions containing both '.' and '>>'/'<<' will change in PHP 8: '<<'/'>>' will take a higher precedence");
+	}
+	if (opcode == ZEND_PARENTHESIZED_CONCAT) {
+		opcode = ZEND_CONCAT;
+	}
+
 	znode left_node, right_node;
 	zend_compile_expr(&left_node, left_ast);
 	zend_compile_expr(&right_node, right_ast);

Zend/zend_compile.h

@@ -1003,11 +1003,11 @@ static zend_always_inline int zend_check_arg_send_type(const zend_function *zf,
 #define ZEND_SYMBOL_CONST    (1<<2)
 
 /* Pseudo-opcodes that are used only temporarily during compilation */
+#define ZEND_PARENTHESIZED_CONCAT 252 /* removed with PHP 8 */
 #define ZEND_GOTO  253
 #define ZEND_BRK   254
 #define ZEND_CONT  255
 
-
 END_EXTERN_C()
 
 #define ZEND_CLONE_FUNC_NAME		"__clone"

Zend/zend_language_parser.y

@@ -957,7 +957,7 @@ expr:
 			{ $$ = zend_ast_create_binary_op(ZEND_SPACESHIP, $1, $3); }
 	|	expr T_INSTANCEOF class_name_reference
 			{ $$ = zend_ast_create(ZEND_AST_INSTANCEOF, $1, $3); }
-	|	'(' expr ')' { $$ = $2; }
+	|	'(' expr ')' { $$ = $2; if ($$->kind == ZEND_AST_BINARY_OP && $$->attr == ZEND_CONCAT) $$->attr = ZEND_PARENTHESIZED_CONCAT; }
 	|	new_expr { $$ = $1; }
 	|	expr '?' expr ':' expr
 			{ $$ = zend_ast_create(ZEND_AST_CONDITIONAL, $1, $3, $5); }

Zend/zend_opcode.c

@@ -1041,6 +1041,7 @@ ZEND_API binary_op_type get_binary_op(int opcode)
 		case ZEND_SR:
 		case ZEND_ASSIGN_SR:
 			return (binary_op_type) shift_right_function;
+		case ZEND_PARENTHESIZED_CONCAT:
 		case ZEND_FAST_CONCAT:
 		case ZEND_CONCAT:
 		case ZEND_ASSIGN_CONCAT: