Re: [Boost.Config] Detect compiler support for std::current_exception

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2019-06-06 16:14:27

On 6/6/19 4:53 PM, dariomt--- via Boost wrote:
>>
>>> Are there instructions for developers that I've missed?
>>
>> There are some instructions here:
>>
>>
>> https://www.boost.org/doc/libs/1_70_0/libs/config/doc/html/boost_config/guidelines_for_boost_authors.html#boost_config.guidelines_for_boost_authors.adding_new_defect_macros
>>
>> Thanks!
> I was expecting developer guidelines in the github readme, not in the
> actual library docs! doh!
> 
> I have made a PR #285 and after some trial and error (I only have VS2015
> and VS2017 available to test locally) I think I have something.
> 
> However, in my test I throw and catch exceptions:
> 
> int test()
> {
>    std::exception_ptr ep;
>    try
>    {
>      throw 42;
>    }
>    catch(...)
>    {
>      ep = std::current_exception();
>    }
>    try
>    {
>      std::rethrow_exception(ep);
>    }
>    catch(int i)
>    {
>      // return zero on success
>      return i == 42 ? 0 : 1;
>    }
>    return 1;
> }
> 
> But the CI jobs have gcc and clang configured to compile without exception
> support! And I get errors like:
> 
> libs/config/test/boost_no_cxx11_hdr_exception.ipp:22:5: error: cannot use
> 'throw' with exceptions disabled
>      throw 42;
>      ^
> libs/config/test/boost_no_cxx11_hdr_exception.ipp:20:3: error: cannot use
> 'try' with exceptions disabled
>    try
>    ^
> 
> I have two questions:
> 
> 1) Where are exceptions disabled in the CI jobs? I can't find it in
> the .travis.yml,
> but I can see e.g. clang being invoked with -fno-exceptions

It's in the test/Jamfile.v2 file, look for <exception-handling>off.

> 2) How can I test proper support for std::current_exception() and
> std::rethrow_exception() if exceptions are disabled for the test?

You should probably condition your test on BOOST_NO_EXCEPTIONS and make 
the test no-op when exceptions are disabled.