ClangCL can't use UDL with /std:c++latest


Bugzilla Link	PR40549
Status	NEW
Importance	P enhancement
Reported by	Stephen Kelly (steveire@gmail.com)
Reported on	2019-01-31 09:43:14 -0800
Last modified on	2019-01-31 12:47:10 -0800
Version	trunk
Hardware	PC Windows NT
CC	efriedma@quicinc.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk, rnk@google.com, Tom.Tan@microsoft.com
Fixed by commit(s)
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This occurs while trying to implement a user-defined literal. Attempting to
compile code without char8_t and with

 A a2 = u8"\u4F60\u597D"_sv;

results in

u8.cpp(24,28):  error: no matching literal operator for call to 'operator""_sv'
with arguments of types
      'const char8_t *' and 'unsigned long long', and no matching literal operator template
    A a2 = u8"\u4F60\u597D"_sv;

Trying to add an overload with char8_t results in:

u8.cpp(10,1):  error: cannot mangle this built-in char8_t type yet
A operator "" _sv(const char8_t* str, INT len)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

So, currently UDL can't be used with /std:c++latest

struct A
{
  A()  {}
};

#define INT unsigned long long

#ifdef TRY_U8
A operator "" _sv(const char8_t* str, INT len)
{
    return A{};
}
#endif

A operator "" _sv(const char* str, INT len)
{
    return A{};
}

int main()
{
    A a1 = "hello"_sv;
#ifdef TRY_U8
    A a2 = u8"\u4F60\u597D"_sv;
#endif
}

Quuxplusone / LLVMBugzillaTest

ClangCL can't use UDL with /std:c++latest #39520