[RFC] Catch exceptions without capturing them to variables

The RFC is currently being drafted at
https://wiki.php.net/rfc/non-capturing_catches

Author: MaxSem

Zend/tests/try/catch_novar_1.phpt

@@ -0,0 +1,31 @@
+--TEST--
+catch without capturing a variable
+--FILE--
+
+
+try {
+    throw new Exception();
+} catch (Exception) {
+    echo "Exception\n";
+}
+
+try {
+    throw new Exception();
+} catch (Exception) {
+    echo "Exception\n";
+} catch (Error) {
+    echo "FAIL\n";
+}
+
+try {
+    throw new Exception();
+} catch (Exception|Error) {
+    echo "Exception\n";
+} catch (Throwable) {
+    echo "FAIL\n";
+}
+
+--EXPECT--
+Exception
+Exception
+Exception

Zend/tests/try/catch_novar_2.phpt

@@ -0,0 +1,19 @@
+--TEST--
+catch without capturing a variable - exception in destructor
+--FILE--
+
+class ThrowsOnDestruct extends Exception {
+    public function __destruct() {
+        echo "Throwing\n";
+        throw new RuntimeException(__METHOD__);
+    }
+}
+try {
+    throw new ThrowsOnDestruct();
+} catch (Exception $ex) {
+    echo "Unreachable catch\n";
+}
+echo "Unreachable fallthrough\n";
+
+--EXPECT--
+Throwing

Zend/zend_ast.c

@@ -1992,8 +1992,10 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 		case ZEND_AST_CATCH:
 			smart_str_appends(str, "} catch (");
 			zend_ast_export_catch_name_list(str, zend_ast_get_list(ast->child[0]), indent);
-			smart_str_appends(str, " $");
-			zend_ast_export_var(str, ast->child[1], 0, indent);
+			if (ast->child[1]) {
+				smart_str_appends(str, " $");
+				zend_ast_export_var(str, ast->child[1], 0, indent);
+			}
 			smart_str_appends(str, ") {\n");
 			zend_ast_export_stmt(str, ast->child[2], indent + 1);
 			zend_ast_export_indent(str, indent);

Zend/zend_compile.c

@@ -5202,7 +5202,7 @@ void zend_compile_try(zend_ast *ast) /* {{{ */
 		zend_ast_list *classes = zend_ast_get_list(catch_ast->child[0]);
 		zend_ast *var_ast = catch_ast->child[1];
 		zend_ast *stmt_ast = catch_ast->child[2];
-		zend_string *var_name = zval_make_interned_string(zend_ast_get_zval(var_ast));
+		zend_string *var_name = var_ast ? zval_make_interned_string(zend_ast_get_zval(var_ast)) : NULL;
 		zend_bool is_last_catch = (i + 1 == catches->children);
 
 		uint32_t *jmp_multicatch = safe_emalloc(sizeof(uint32_t), classes->children - 1, 0);
@@ -5230,12 +5230,12 @@ void zend_compile_try(zend_ast *ast) /* {{{ */
 					zend_resolve_class_name_ast(class_ast));
 			opline->extended_value = zend_alloc_cache_slot();
 
-			if (zend_string_equals_literal(var_name, "this")) {
+			if (var_name && zend_string_equals_literal(var_name, "this")) {
 				zend_error_noreturn(E_COMPILE_ERROR, "Cannot re-assign $this");
 			}
 
-			opline->result_type = IS_CV;
-			opline->result.var = lookup_cv(var_name);
+			opline->result_type = var_name ? IS_CV : IS_UNUSED;
+			opline->result.var = var_name ? lookup_cv(var_name) : -1;
 
 			if (is_last_catch && is_last_class) {
 				opline->extended_value |= ZEND_LAST_CATCH;

Zend/zend_language_parser.y

@@ -248,7 +248,7 @@ static YYSIZE_T zend_yytnamerr(char*, const char*);
 %type  encaps_var encaps_var_offset isset_variables
 %type  top_statement_list use_declarations const_list inner_statement_list if_stmt
 %type  alt_if_stmt for_exprs switch_case_list global_var_list static_var_list
-%type  echo_expr_list unset_variables catch_name_list catch_list parameter_list class_statement_list
+%type  echo_expr_list unset_variables catch_name_list catch_list optional_variable parameter_list class_statement_list
 %type  implements_list case_list if_stmt_without_else
 %type  non_empty_parameter_list argument_list non_empty_argument_list property_list
 %type  class_const_list class_const_decl class_name_list trait_adaptations method_body non_empty_for_exprs
@@ -465,7 +465,7 @@ statement:
 catch_list:
 		%empty
 			{ $$ = zend_ast_create_list(0, ZEND_AST_CATCH_LIST); }
-	|	catch_list T_CATCH '(' catch_name_list T_VARIABLE ')' '{' inner_statement_list '}'
+	|	catch_list T_CATCH '(' catch_name_list optional_variable ')' '{' inner_statement_list '}'
 			{ $$ = zend_ast_list_add($1, zend_ast_create(ZEND_AST_CATCH, $4, $5, $8)); }
 ;
 
@@ -474,6 +474,11 @@ catch_name_list:
 	|	catch_name_list '|' class_name { $$ = zend_ast_list_add($1, $3); }
 ;
 
+optional_variable:
+		%empty { $$ = NULL; }
+	|	T_VARIABLE { $$ = $1; }
+;
+
 finally_statement:
 		%empty { $$ = NULL; }
 	|	T_FINALLY '{' inner_statement_list '}' { $$ = $3; }

Zend/zend_vm_def.h

@@ -4486,12 +4486,16 @@ ZEND_VM_HANDLER(107, ZEND_CATCH, CONST, JMP_ADDR, LAST_CATCH|CACHE_SLOT)
 	}
 
 	exception = EG(exception);
-	ex = EX_VAR(opline->result.var);
-	if (UNEXPECTED(Z_ISREF_P(ex))) {
-		ex = Z_REFVAL_P(ex);
+	if (RETURN_VALUE_USED(opline)) {
+		ex = EX_VAR(opline->result.var);
+		if (UNEXPECTED(Z_ISREF_P(ex))) {
+			ex = Z_REFVAL_P(ex);
+		}
+		zval_ptr_dtor(ex);
+		ZVAL_OBJ(ex, EG(exception));
+	} else {
+		OBJ_RELEASE(EG(exception));
 	}
-	zval_ptr_dtor(ex);
-	ZVAL_OBJ(ex, EG(exception));
 	if (UNEXPECTED(EG(exception) != exception)) {
 		GC_ADDREF(EG(exception));
 		HANDLE_EXCEPTION();

Zend/zend_vm_execute.h

@@ -3702,12 +3702,16 @@ static ZEND_OPCODE_HANDLER_RET ZEND_FASTCALL ZEND_CATCH_SPEC_CONST_HANDLER(ZEND_
 	}
 
 	exception = EG(exception);
-	ex = EX_VAR(opline->result.var);
-	if (UNEXPECTED(Z_ISREF_P(ex))) {
-		ex = Z_REFVAL_P(ex);
+	if (RETURN_VALUE_USED(opline)) {
+		ex = EX_VAR(opline->result.var);
+		if (UNEXPECTED(Z_ISREF_P(ex))) {
+			ex = Z_REFVAL_P(ex);
+		}
+		zval_ptr_dtor(ex);
+		ZVAL_OBJ(ex, EG(exception));
+	} else {
+		OBJ_RELEASE(EG(exception));
 	}
-	zval_ptr_dtor(ex);
-	ZVAL_OBJ(ex, EG(exception));
 	if (UNEXPECTED(EG(exception) != exception)) {
 		GC_ADDREF(EG(exception));
 		HANDLE_EXCEPTION();