Support catching exceptions without capturing them to variables

RFC: https://wiki.php.net/rfc/non-capturing_catches

Closes phpGH-5345.

UPGRADING

@@ -509,6 +509,9 @@ PHP 8.0 UPGRADE NOTES
     RFC: https://wiki.php.net/rfc/throw_expression
   . An optional trailing comma is now allowed in parameter lists.
     RFC: https://wiki.php.net/rfc/trailing_comma_in_parameter_list
+  . It is now possible to write `catch (Exception)` to catch an exception
+    without storing it in a variable.
+    RFC: https://wiki.php.net/rfc/non-capturing_catches
 
 - Date:
   . Added DateTime::createFromInterface() and

Zend/tests/try/catch_novar_1.phpt

@@ -0,0 +1,31 @@
+--TEST--
+catch without capturing a variable
+--FILE--
+<?php
+
+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 +1,26 @@
+--TEST--
+catch without capturing a variable - exception in destructor
+--FILE--
+<?php
+class ThrowsOnDestruct extends Exception {
+    public function __destruct() {
+        echo "Throwing\n";
+        throw new RuntimeException(__METHOD__);
+    }
+}
+try {
+    throw new ThrowsOnDestruct();
+} catch (Exception) {
+    echo "Unreachable catch\n";
+}
+echo "Unreachable fallthrough\n";
+
+?>
+--EXPECTF--
+Throwing
+
+Fatal error: Uncaught RuntimeException: ThrowsOnDestruct::__destruct in %s:%d
+Stack trace:
+#0 %s(%d): ThrowsOnDestruct->__destruct()
+#1 {main}
+  thrown in %s on line %d

Zend/zend_ast.c

@@ -1993,8 +1993,10 @@ 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

@@ -5213,7 +5213,7 @@ 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);
@@ -5241,12 +5241,12 @@ 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 <ast> encaps_var encaps_var_offset isset_variables
 %type <ast> top_statement_list use_declarations const_list inner_statement_list if_stmt
 %type <ast> alt_if_stmt for_exprs switch_case_list global_var_list static_var_list
-%type <ast> echo_expr_list unset_variables catch_name_list catch_list parameter_list class_statement_list
+%type <ast> echo_expr_list unset_variables catch_name_list catch_list optional_variable parameter_list class_statement_list
 %type <ast> implements_list case_list if_stmt_without_else
 %type <ast> non_empty_parameter_list argument_list non_empty_argument_list property_list
 %type <ast> 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

@@ -4453,7 +4453,6 @@ ZEND_VM_HANDLER(107, ZEND_CATCH, CONST, JMP_ADDR, LAST_CATCH|CACHE_SLOT)
 	USE_OPLINE
 	zend_class_entry *ce, *catch_ce;
 	zend_object *exception;
-	zval *ex;
 
 	SAVE_OPLINE();
 	/* Check whether an exception has been thrown, if not, jump over code */
@@ -4486,17 +4485,18 @@ ZEND_VM_HANDLER(107, ZEND_CATCH, CONST, JMP_ADDR, LAST_CATCH|CACHE_SLOT)
 	}
 
 	exception = EG(exception);
-	ex = EX_VAR(opline->result.var);
-	{
+	EG(exception) = NULL;
+	if (RETURN_VALUE_USED(opline)) {
 		/* Always perform a strict assignment. There is a reasonable expectation that if you
 		 * write "catch (Exception $e)" then $e will actually be instanceof Exception. As such,
 		 * we should not permit coercion to string here. */
 		zval tmp;
 		ZVAL_OBJ(&tmp, exception);
-		EG(exception) = NULL;
-		zend_assign_to_variable(ex, &tmp, IS_TMP_VAR, /* strict */ 1);
-		ZEND_VM_NEXT_OPCODE_CHECK_EXCEPTION();
+		zend_assign_to_variable(EX_VAR(opline->result.var), &tmp, IS_TMP_VAR, /* strict */ 1);
+	} else {
+		OBJ_RELEASE(exception);
 	}
+	ZEND_VM_NEXT_OPCODE_CHECK_EXCEPTION();
 }
 
 ZEND_VM_HOT_HANDLER(65, ZEND_SEND_VAL, CONST|TMPVAR, NUM)

Zend/zend_vm_execute.h

@@ -3669,7 +3669,6 @@ static ZEND_OPCODE_HANDLER_RET ZEND_FASTCALL ZEND_CATCH_SPEC_CONST_HANDLER(ZEND_
 	USE_OPLINE
 	zend_class_entry *ce, *catch_ce;
 	zend_object *exception;
-	zval *ex;
 
 	SAVE_OPLINE();
 	/* Check whether an exception has been thrown, if not, jump over code */
@@ -3702,17 +3701,18 @@ static ZEND_OPCODE_HANDLER_RET ZEND_FASTCALL ZEND_CATCH_SPEC_CONST_HANDLER(ZEND_
 	}
 
 	exception = EG(exception);
-	ex = EX_VAR(opline->result.var);
-	{
+	EG(exception) = NULL;
+	if (RETURN_VALUE_USED(opline)) {
 		/* Always perform a strict assignment. There is a reasonable expectation that if you
 		 * write "catch (Exception $e)" then $e will actually be instanceof Exception. As such,
 		 * we should not permit coercion to string here. */
 		zval tmp;
 		ZVAL_OBJ(&tmp, exception);
-		EG(exception) = NULL;
-		zend_assign_to_variable(ex, &tmp, IS_TMP_VAR, /* strict */ 1);
-		ZEND_VM_NEXT_OPCODE_CHECK_EXCEPTION();
+		zend_assign_to_variable(EX_VAR(opline->result.var), &tmp, IS_TMP_VAR, /* strict */ 1);
+	} else {
+		OBJ_RELEASE(exception);
 	}
+	ZEND_VM_NEXT_OPCODE_CHECK_EXCEPTION();
 }
 
 static ZEND_VM_HOT ZEND_OPCODE_HANDLER_RET ZEND_FASTCALL ZEND_SEND_VAL_SPEC_CONST_HANDLER(ZEND_OPCODE_HANDLER_ARGS)