`<source_location>`: Use `__builtin_FUNCSIG` when Clang 17 is available

[JMazurkiewicz]

I've implemented __builtin_FUNCSIG in Clang recently (llvm/llvm-project@78d8312):

const char* __builtin_FUNCSIG();

We should use this builtin in source_location implementation after VS gets Clang 17:

STL/stl/inc/source_location

Lines 28 to 32 in a621095

	#if defined(__clang__) || defined(__EDG__) // TRANSITION, DevCom-10199227 and LLVM-58951
	const char* const _Function_ = __builtin_FUNCTION()
	#else // ^^^ workaround / no workaround vvv
	const char* const _Function_ = __builtin_FUNCSIG()
	#endif // TRANSITION, DevCom-10199227 and LLVM-58951

Comparison:

// https://godbolt.org/z/zq6v9v87q
#include <iostream>

void f(const char* old_ = __builtin_FUNCTION(), const char* new_ = __builtin_FUNCSIG()) {
    std::cout << "old: " << old_ << "\nnew: " << new_ << '\n';
}

int main() {
    f();
}

old: main
new: int __cdecl main(void)

[nuuSolutions]

I'm wondering why we can't have both the simple function name as well as the full signature.

Alternatively: How would I best go about extending/modifying this to my needs? (not only on clang)

[sylveon]

You can always just copy the definition of source_location and customize it to your needs.

[CaseyCarter]

Interestingly, __has_builtin(__builtin_FUNCSIG) doesn't appear to work: https://godbolt.org/z/6Tsa55j8T

Maybe it's only available in MSVC mode? Yeah (IIRC this is rc4):

C:\Users\cacarter\OneDrive - Microsoft\Desktop>type repro.cpp
#include <cstdio>

int main() {
#if __has_builtin(__builtin_FUNCSIG)
    std::puts("has it");
#else
    std::puts("does NOT have it");
#endif
}

C:\Users\cacarter\OneDrive - Microsoft\Desktop>"c:\Program Files\LLVM\bin\clang-cl.exe" --version
clang version 17.0.0
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: c:\Program Files\LLVM\bin

C:\Users\cacarter\OneDrive - Microsoft\Desktop>"c:\Program Files\LLVM\bin\clang-cl.exe" "c:\Users\cacarter\OneDrive - Microsoft\Desktop\repro.cpp" && repro
has it

[StephanTLavavej]

Oh thanks - I deleted my comments because I had gotten very confused about what I was seeing on Compiler Explorer.

[nuuSolutions]

I'm more confused that Intellisense shows __builtin_FUNCSIG as an error while does compile & work fine (with msvc 1937)
I'm even more confused that such trivial things are not implemented/implementable in a consistent way across platforms

I did indeed have to adapt std::source_location to include what I need (i.e. the simple function name)

[StephanTLavavej]

IntelliSense is powered by a different compiler front-end (EDG). MSVC's "C1XX" front-end is what's used by cl.exe to actually compile code.