[libcxx-dev] LLVM libcxx "hash" clashes with custom define "hash"

[Marshall Clow via libcxx-dev]

On Jul 29, 2020, at 5:32 AM, Oliver Major via libcxx-dev <libcxx-dev at lists.llvm.org> wrote:
> 
> Hello everyone,
> 
> I am new here and in fact not subscribed, I just have a question and don't even know if I am at the right address.
> 
> We recently found a bug in our product code when building with NDK Clang for Android and it is related to the LLVM libcxx. It is fairly easy to reproduce and a quick internet search reveals that we are not the only ones with this or a similar issue.
> 
> What we did, was
> #define hash #
> 
> before
> #include <math.h>
> 
> which let to a problem with libcxx/include/type_traits:417  
> template <class _Tp> struct _LIBCPP_TEMPLATE_VIS hash; 
> 
> of course. We obviously shouldn't let defines leak into the stdlib, so it is our fault, we fixed it simply by renaming the define.

Good.

> 
> I didn't want to post it as a bug in the LLVM bugtracker, because I don't even think it needs fixing on LLVM side. I just wanted to make aware that this issue exists for some people and wanted to ask if there is a way to publicly document this issue somewhere, so people having problems with this can potentially find a solution on the internet.

You’re not allowed to #define names that are defined in the standard library..
See http://eel.is/c++draft/macro.names <http://eel.is/c++draft/macro.names>, which states:

A translation unit that includes a standard library header shall not #define or #undef names declared in any standard library header.

— Marshall
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