Re: Boost.Exception regression in 1.75.0 beta 1

From: Marshall Clow (mclow.lists_at_[hidden])
Date: 2020-11-14 01:08:22

On Nov 13, 2020, at 3:17 AM, Niall Douglas via Boost <boost_at_[hidden]> wrote:
> 
> If you diagnose the test failures (which are present across all
> compilers) in
> https://www.boost.org/development/tests/develop/developer/outcome.html
> which report failures of the form:
> 
> ```
> unknown location(0): fatal error: in "works_outcome": Throw location
> unknown (consider using BOOST_THROW_EXCEPTION)
> Dynamic exception type: struct boost::wrapexcept<class boost::exception_ptr>
> 
> libs\outcome\test\tests\core-outcome.cpp(173): last checkpoint
> 
> *** 1 failure is detected in the test module "Outcome"
> ```
> 
> The cause is test code such as:
> 
> ```
>    boost::system::error_code ec(5, boost::system::system_category());
>    auto e = boost::copy_exception(boost::system::system_error(ec));  //
> NOLINT
>    outcome<int> m(e);
>    BOOST_CHECK_THROW(m.value(), boost::system::system_error);
> ```
> 
> Outcome calls boost::rethrow_exception() to rethrow the exception_ptr.
> boost::rethrow_exception() is not rethrowing the
> boost::system::system_error held within the boost::exception_ptr. It is
> throwing instead boost::wrapexcept<class boost::exception_ptr>. This
> causes BOOST_CHECK_THROW() to not correctly trap the type of exception
> thrown, and thus the test fails.
> 
> boost::wrapexcept<E> inherits from E. It seems to me therefore that
> catching a const E& ought to catch throws of boost::wrapexcept<E>, and
> therefore this code is correct. I double checked this at
> https://wandbox.org/permlink/n9Wjb5cPpfHEFalp, and indeed it works as
> expected.
> 
> However, obviously enough this is failing, and it was not failing in
> Boost 1.74, so this is a regression. I am stumped as to the exact cause.
> 
> This affects all platforms, POSIX, Windows, clang, GCC and MSVC.

I think that this can be fixed post-beta.

— Marshall