Apple Clang: std::source_location returns a wrong results if called in a function parameter.

[H-G-Hristov]

This is more of a question. The examples in this article as seen on Compiler Explorer (trunk) work as expected but in Xcode 15 they return the location of the std::source_location::current() call. Could that be a bug in Apple Clang 15.0?

https://www.cppstories.com/2021/non-terminal-variadic-args/

template <typename... Ts>
struct Logger
{
    Logger(Ts&&... ts, const std::source_location& loc = std::source_location::current())
    {
        std::cout << loc.function_name() << " line " << loc.line() << ": ";
        ((std::cout << std::forward<Ts>(ts) << " "), ...);
        std::cout << '\n';
    }
};

template <typename... Ts>
Logger(Ts&&...) -> Logger<Ts...>;

Apple Clang 15 output (wrong):

> % ./nagent
Logger<const char (&)[26], int, int, int, int>::Logger(Ts &&..., const std::source_location &) [Ts = <const char (&)[26], int, int, int, int>] line 281: Alabalanica turska panica 1 2 3 5 

GCC 13.2 output (correct):

>  # ./nagent
int main(int, char**) line 295: Alabalanica turska panica 1 2 3 5 

Apple Clang details:

> % clang --version
Apple clang version 15.0.0 (clang-1500.0.40.1)
Target: arm64-apple-darwin23.0.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

[DimitryAndric]

If it is only reproducible with Apple clang, please file a bug report with Apple. Do you have a complete example that you can post in this bug, instead of referring to godbolt or some other site?

[H-G-Hristov]

If it is only reproducible with Apple clang, please file a bug report with Apple. Do you have a complete example that you can post in this bug, instead of referring to godbolt or some other site?

This should do:

#include <iostream>
#include <string_view>
#include <source_location>
#include <fmt/core.h>

struct Logger {
    Logger(std::source_location l = std::source_location::current()) : loc(std::move(l)) { }
    
    template <typename ...Args>
    void debug(std::string_view format, Args&& ...args) {
	    std::cout << fmt::format("{}({}) ", loc.file_name(), loc.line())
                  << fmt::format(format, std::forward<Args>(args)...) << '\n';
    }
    
private:
    std::source_location loc;    
};
 
int main() {
    std::cout << sizeof(std::source_location) << '\n';
    Logger().debug("{}, {}", "hello", "world");
    Logger().debug("{}, {}", 10, 42);
}

I hope this is Apple's Clang repository: apple#7562

[tbaederr]

IIRC @cor3ntin fixed that for clang 17(?)

[cor3ntin]

This has been working since clang 16
https://compiler-explorer.com/z/o7T8jbh3a

Sadly it's difficult to map a version of clang to a version of AppleClang, and I don't know how fast Apple has been at adopting Clang 16. Because this is a question for the Apple-shipped version of clang, I think we can close this issue.

(apple#7562 does seem to be the appropriate place for this!)