[cmake-developers] I fear $<COMPILE_FEATURES:*> is not really useful...

[Rolf Eike Beer]

Yes, sadly. I have this code:

if (NOT CMAKE_VERSION VERSION_LESS 3.1)
   set_property(TARGET osmium_convert PROPERTY CXX_STANDARD 11)
   target_compile_definitions(osmium_convert PRIVATE 
$<$<COMPILE_FEATURES:cxx_decltype_incomplete_return_types>:BOOST_RESULT_OF_USE_DECLTYPE>)
endif()

So, in theory, this will set the definition if the compiler supports decltype, 
and just don't set it if not. And it works fine for g++. The problem is when it 
comes to MSVC:

There is no MSVC version that supports this feature properly, so there is no 
variable for this compiler defined. Or just think of $FooBarC++, where noone 
cared to report the supported features. No variable either. For these 
compilers the above expression fails, because this is no recorded feature of 
the compiler. I would have expected it to just not set the definition, but not 
error out.

So for now my code is:

if (NOT CMAKE_VERSION VERSION_LESS 3.1 AND CMAKE_CXX_COMPILER_ID STREQUAL 
"GNU")
 ...

Greetings,

Eike
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