EDG hasn't implemented CWG-2256 "Lifetime of trivially-destructible objects"

[StephanTLavavej]

Issue Summary

I'm the primary maintainer of microsoft/STL, and we've encountered a bug in EDG, which we're working around in the STL. Using VS Insiders / MSVC Build Tools Preview, the following code is correctly accepted by the MSVC Compiler 19.52.36815 and Clang 22.1.3, but incorrectly rejected by EDG 6.9. This is using MSVC's undocumented /BE option to invoke VS's copy of the EDG frontend used for IntelliSense.

See CWG-2256 "Lifetime of trivially-destructible objects" which was "Accepted as a DR at the February, 2019 meeting."

We didn't manage to report this to EDG before it was open-sourced, because MSVC mishandled this code at that time, but MSVC has since been fixed. (For my own reference, this was also DevCom-10896316 and MSVC-internal VSO-2459167.)

Reproducing Source Code

template <auto>
struct required_valid_constant_expression;

struct S {
    int n;
};

struct S2 {
    int n;
    constexpr ~S2() {} // non-trivial
};

template <class C, class Fn>
constexpr int consteval_validate_destruction(Fn op) {
    C x{42};
    op(x);
    return x.n;
}

template <class C, auto Fn>
constexpr bool CanWellDefinedlyAccessAfterOperation =
    requires { typename required_valid_constant_expression<consteval_validate_destruction<C>(Fn)>; };

constexpr auto destruction_op = []<class T>(T& x) { x.~T(); };

static_assert(!CanWellDefinedlyAccessAfterOperation<S, destruction_op>);
static_assert(!CanWellDefinedlyAccessAfterOperation<S2, destruction_op>);

Command-line Options

cl /EHsc /nologo /W4 /std:c++latest /c /BE /dE--version meow.cpp

Type of Issue

[Front End] This code SHOULD compile with these options.

Additional Details

Compiler output showing how MSVC and Clang accept while EDG rejects:

C:\Temp>cl
Microsoft (R) C/C++ Optimizing Compiler Version 19.52.36815 for x64 (PREVIEW)
Copyright (C) Microsoft Corporation.  All rights reserved.

usage: cl [ option... ] filename... [ /link linkoption... ]

C:\Temp>cl /EHsc /nologo /W4 /std:c++latest /c meow.cpp
meow.cpp

C:\Temp>clang-cl -v
clang version 22.1.3 (https://github.com/llvm/llvm-project e9846648fd6183ee6d8cbdb4502213fcf902a211)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Program Files\Microsoft Visual Studio\18\Insiders\VC\Tools\Llvm\x64\bin

C:\Temp>clang-cl /EHsc /nologo /W4 /std:c++latest /c meow.cpp

C:\Temp>cl /EHsc /nologo /W4 /std:c++latest /c /BE /dE--version meow.cpp
meow.cpp
Edison Design Group C/C++ Front End, version 6.9 (Sep 15 2026 13:46:37)
Copyright 1988-2026 Edison Design Group, Inc.

"meow.cpp", line 26: error: static assertion failed
  static_assert(!CanWellDefinedlyAccessAfterOperation<S, destruction_op>);
  ^

Reproducing (Standard) Configuration(s)

windows-msvc-release

Reproducing (Non-standard) Configuration

dump_configuration.txt

I acknowledge that:

• I have checked open issues and existing discussions before filing this report.
• The reproducing source code that I have provided does not depend on headers that I have not included with my submission.
• I have reduced the reproducing source code to the best of my ability.
• I have selected at least one standard configuration or uploaded a non-standard configuration dump.
• I understand code shared via this form is NOT confidential.
• I have permission to share the reproducing source code and grant permission for the project to use the source code (or derivatives of the source code) to create tests.
• I agree that any tests created using the reproducing source code (or deriatives of it) will be licensed under project license unless I included a LICENSE.txt file in my .zip or .tar.gz upload. If I included a LICENSE.txt file, any tests created using the reproducing source code will be governed by the terms of the license I provided instead.