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From: Alexander Grund (alexander.grund_at_[hidden])
Date: 2021-02-02 16:40:36

Am 02.02.21 um 17:25 schrieb Andrey Semashev via Boost:
> On 2/2/21 7:09 PM, Alexander Grund via Boost wrote:
>> Peter and I found a simple way to reproduce the behavior I was seeing
>> on Mac: Use libc++
>> `./b2 link=shared libs/program_options/test/ toolset=clang
>> stdlib=libc++` is enough to reproduce the problem.
>> I'm actually surprised that this hasn't come up before. No tests for
>> all boost with libc++?
> I suspect, Mac OS (more precisely, its linker) is the crucial part,
> not libc++. clang+libc++ on Linux is relatively well tested (or at
> least used to be, when Travis was more usable), but Mac OS is less
> tested because of slow turnaround.

The above command which tests Boost.ProgramOptions using clang + libc++
on Linux shows the same failure I see on OSX due to using DECL instead
of VISIBLE on the exception class defined in the header. So this setting
is obviously untested, which I find odd.

IIRC OSX uses libc++ too which explains the correlation.

>>> BOOST_SYMBOL_IMPORT doesn't need to expand to BOOST_SYMBOL_VISIBLE
>>> when the marked symbols are only defined in the library, which is
>>> the case normally. When the user consumes the library, no markup is
>>> needed as the compiler will simply leave unresolved references to
>>> those symbols, to be resolved by the linker.
>>>  Basically, BOOST_SYMBOL_IMPORT is only there for compatibility with
>>> Windows.
>> Agreed with the first part.
>> But quite many are defined in headers, especially the exceptions, so
>> there it is required.
> For classes defined in a header, neither EXPORT nor IMPORT are needed.
> Only VISIBLE is, if you need publicly visible RTTI.

Ok great, so we have a few actual bugs now: Not using VISIBLE for those.

Next issue are classes declared in the header and defined in a cpp file
which should be (able to be) caught by consumers. Due to the definition
in the CPP I think they need the DECL (->EXPORT/IMPORT) but also VISIBLE.

For comparison again: CMake defines the IMPORT macro to VISIBLE, so
that's a datapoint at least:

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