| Summary: | [DR 2256] Can't jump into scope of a variable with a nontrivial destructor in C++20 | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Joseph C. Sible <josephcsible> |
| Component: | c++ | Assignee: | Patrick Palka <ppalka> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | ppalka, webrown.cpp |
| Priority: | P3 | Keywords: | rejects-valid |
| Version: | 11.2.1 | ||
| Target Milestone: | 14.0 | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2021-11-05 00:00:00 | |
| Bug Depends on: | |||
| Bug Blocks: | 94404 | ||
Confirmed. The C++ spec was changed by DR2256 which is consider CD5. (In reply to Andrew Pinski from comment #2) > which is consider CD5. That's just a detail of which draft of was included in, which doesn't mean much. More relevant is that it was approved as a DR so it applies to C++17 (and earlier) too. The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>: https://gcc.gnu.org/g:b81785eacef2a28e17e17141fcd334f51640feec commit r14-563-gb81785eacef2a28e17e17141fcd334f51640feec Author: Patrick Palka <ppalka@redhat.com> Date: Sun May 7 12:09:03 2023 -0400 c++: goto entering scope of obj w/ non-trivial dtor [PR103091] It seems ever since DR 2256 goto is permitted to cross the initialization of a trivially initialized object with a non-trivial destructor. We already supported this as an -fpermissive extension, so this patch just makes us unconditionally support this. DR 2256 PR c++/103091 gcc/cp/ChangeLog: * decl.cc (decl_jump_unsafe): Return bool instead of int. Don't consider TYPE_HAS_NONTRIVIAL_DESTRUCTOR. (check_previous_goto_1): Simplify now that decl_jump_unsafe returns bool instead of int. (check_goto): Likewise. gcc/testsuite/ChangeLog: * g++.old-deja/g++.other/init9.C: Don't expect diagnostics for goto made valid by DR 2256. * g++.dg/init/goto4.C: New test. Fixed for GCC 14, thanks for the report. |
The C++17 standard says "A program that jumps from a point where a variable with automatic storage duration is not in scope to a point where it is in scope is ill-formed unless the variable has scalar type, class type with a trivial default constructor and a trivial destructor, a cv-qualified version of one of these types, or an array of one of the preceding types and is declared without an initializer (11.6)." The C++20 standard says "A program that jumps from a point where a variable with automatic storage duration is not in scope to a point where it is in scope is ill-formed unless the variable has vacuous initialization (6.7.3)." and "A variable is said to have vacuous initialization if it is default-initialized and, if it is of class type or a (possibly multi-dimensional) array thereof, that class type has a trivial default constructor." Note that the C++17 standard mentions a trivial destructor here, but the C++20 standard does not. Now consider this code: struct MyStruct { ~MyStruct() {} }; void foo() { goto x; MyStruct s; x: return; } It's ill-formed in C++17, but fine in C++20. However, we currently reject this program even with -std=c++20.