Re: Boost.Exception regression in 1.75.0 beta 1

From: Peter Dimov (pdimov_at_[hidden])
Date: 2020-11-13 13:46:30

Niall Douglas 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.

The same example without use of outcome works:

#include <boost/exception_ptr.hpp>
#include <boost/system/error_code.hpp>
#include <boost/system/system_error.hpp>
#include <boost/core/lightweight_test.hpp>

int main()
{
    boost::system::error_code ec(5, boost::system::system_category());
    auto e = boost::copy_exception(boost::system::system_error(ec));
    BOOST_TEST_THROWS(boost::rethrow_exception(e), 
boost::system::system_error);

    return boost::report_errors();
}

so there's some interaction with outcome here.