<locale>: Repair std::collate<unsigned short>

[Julian Müller (muellerj2)]

This repairs collate<unsigned short> by adding two missing unsigned short specializations for _LStrcoll and _LStrxfrm when we're building the STL. Fixes #5236.

There are similar specializations for a few functions in <xlocale>. I guess _LStrcoll and _LStrxfrm were missed because they are located in a different header.

Since collate is the only user of these functions, I also moved them from <xlocinfo> to <locale> just above collate.

As for why this also fixes collate<wchar_t> = collate<unsigned short> under non-native wchar_t when linking to the DLL, this is because the the locale facets are constructed in the DLL here:

STL/stl/src/wlocale.cpp

Lines 58 to 88 in f2a2933

	// moved from locale to ease subsetting
	using _Tu1 = ctype<unsigned short>;
	using _Tu2 = num_get<unsigned short>;
	using _Tu3 = num_put<unsigned short>;
	using _Tu4 = numpunct<unsigned short>;
	using _Tu5 = collate<unsigned short>;
	using _Tu6 = messages<unsigned short>;
	using _Tu7 = money_get<unsigned short>;
	using _Tu8 = money_put<unsigned short>;
	using _Tu9 = moneypunct<unsigned short, false>;
	using _Tu10 = moneypunct<unsigned short, true>;
	using _Tu11 = time_get<unsigned short>;
	using _Tu12 = time_put<unsigned short>;
	using _Tu13 = codecvt<unsigned short, char, _Mbstatet>;
	void __CLRCALL_OR_CDECL locale::_Locimp::_Makeushloc(const _Locinfo& lobj, locale::category cat, _Locimp* ptrimp,
	const locale* ptrloc) { // setup wide part of a new locale
	ADDFAC(_Tu1, cat, ptrimp, ptrloc);
	ADDFAC(_Tu2, cat, ptrimp, ptrloc);
	ADDFAC(_Tu3, cat, ptrimp, ptrloc);
	ADDFAC(_Tu4, cat, ptrimp, ptrloc);
	ADDFAC(_Tu5, cat, ptrimp, ptrloc);
	ADDFAC(_Tu6, cat, ptrimp, ptrloc);
	ADDFAC(_Tu7, cat, ptrimp, ptrloc);
	ADDFAC(_Tu8, cat, ptrimp, ptrloc);
	ADDFAC(_Tu9, cat, ptrimp, ptrloc);
	ADDFAC(_Tu10, cat, ptrimp, ptrloc);
	ADDFAC(_Tu11, cat, ptrimp, ptrloc);
	ADDFAC(_Tu12, cat, ptrimp, ptrloc);
	ADDFAC(_Tu13, cat, ptrimp, ptrloc);
	}

Thus, collate's virtual functions originate from the DLL as well. These virtual functions call _LStrcoll and _LStrxfrm, but the specializations for unsigned short were missing since the DLL is built with native wchar_t.

In the new test, we have to skip collate::transform() tests when there is IDL mismatch between TU and linked DLL.

[Stephan T. Lavavej (StephanTLavavej)]

Thanks! I updated the product code's preprocessor logic, pushed significant changes to the test, and updated the PR description accordingly - please meow if I messed something up.

The general principle that we now follow (although our legacy codebase didn't) is that while /Zc:wchar_t- should work (fake wchar_t), normal users of /Zc:wchar_t (real wchar_t) should not experience unsigned short as anything special. Only the STL's separately compiled code has to worry about real and fake wchar_t simultaneously.

[Stephan T. Lavavej (StephanTLavavej)]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[Stephan T. Lavavej (StephanTLavavej)]

Thanks for fixing the world's best library with the world's worst compiler option! 😹 💚 🎉