Cannot compile with /GR- (RTTI disabled) and _HAS_STATIC_RTTI=0 with MSVC compiler

[inkychris]

I get the following error compiling a CLI11 example with /GR- (RTTI disabled) and also with -D_HAS_STATIC_RTTI=0:

CLI11.hpp(6763,25): error C2280: 'std::shared_ptr<CLI::ConfigBase> std::dynamic_pointer_cast<CLI::ConfigBase,CLI::Config>(const std::shared_ptr<CLI::Config> &) noexcept': attempting to reference a deleted function

The condition check for whether to use a dynamic or static cast is the issue here:

CLI11/include/CLI/App.hpp

Lines 1546 to 1550 in 8155532

	#if defined(__cpp_rtti) || (defined(__GXX_RTTI) && __GXX_RTTI) || (defined(_HAS_STATIC_RTTI) && (_HAS_STATIC_RTTI == 0))
	return std::dynamic_pointer_cast<ConfigBase>(config_formatter_);
	#else
	return std::static_pointer_cast<ConfigBase>(config_formatter_);
	#endif

MSVC does not appear to modify the value of __cpp_rtti which remains 1, but rather sets _CPPRTTI instead. Visual Studio's intellisense doesn't seem to correctly interpret this value but it does in fact change depending on /GR[-].

If my understanding is correct, the condition for _HAS_STATIC_RTTI should also be checking for a value of 1, not 0.

[phlptp]

I think the _HAS_STATIC_RTTI is correct. If that is set you want to use the static cast, it looks like we need to expand the conditions of __cpp_rtti and possibly a similar one for _CPPRTTI

We also might want to flip the conditions a little to better reflect the different possibilities you described. Need to think a little more

[phlptp]

I added a potential fix in #666, not sure if you can check that, or if we should try to tweak one of the CI builds with RTTI disabled like in the issue? @henryiii thoughts?

[inkychris]

I was under the impression that _HAS_STATIC_RTTI=0 defined but disabled it, although I think this STL source suggests I misunderstood this variable, it seems a little backwards to me!

https://github.com/microsoft/STL/blob/178b8406a5647507e759442960f17cd33045cdf5/stl/inc/yvals_core.h#L591-L597

Your changes seem to have fixed the issue for me and it's correctly selecting the static cast now.

[phlptp]

I think I have always interpreted it as if that is set it has RTTI but don't use the dynamic RTTI.

[inkychris]

Yeah that STL snippet I linked seems to agree with you, since it throws an error if you both define _HAS_STATIC_RTTI and have /GR (enable RTTI). I think I need to pull those definitions out of my codebase!

Actually on reflection, I think the value of that definition is taken into consideration, as implied by both these threads:

• https://www.mail-archive.com/[email protected]/msg235273.html
• <functional>: _HAS_STATIC_RTTI=0 shouldn't say typeid(void) microsoft/STL#340

That said, your proposed change is still behaving correctly. CLI11 should be using the static cast if _HAS_STATIC_RTTI=0. The original condition was in fact supposed to be checking for a value of 1 and not 0.