clang and libc++: compile error in json.h

[MichaelSB]

For reasons I tried to compile a simple program with clang++ (13.0.1) and libc++ (13.0.1). I got a monster error message hinting at wvalue& operator=(object const& value) and wvalue& operator=(std::initializer_list<std::pair<std::string const, wvalue>> initializer_list), compiling with clang++ -stdlib=libc++ -I ./Crow/include/ main.cc -o main The error refers to the assignments of value or initializer_list to (*o). wvalue contains unique_ptrs, which can't be copied. So I guess clang++ is right. Using the __APPLE__ or __MACH__ execution path unconditionally fixes the error in my experiments.

[MichaelSB]

Is this a scenario (clang, libc++ on linux) crow should support? I could just "implement" the fix mentioned above. Or dig deeper and try to find out more about the cause of the error. I wonder why this is no problem with libstdc++. This lib should complain about copying unique_ptrs too. I suspect there's a flaw in my analysis so far :)

[The-EDev]

Is this a scenario (clang, libc++ on linux) crow should support?

It absolutely should, I'm guessing this is a problem with our CI process which I should address (that it doesn't test with libc++)

[The-EDev]

This issue seems to be the result of an oversight in #242. The workaround is already in place, but my guess is that MacOS uses libc++ by default, which is why I assumed the bug was related to the OS rather than the standard template library.

I'm sorry it took me this long to investigate.

[The-EDev]

The fix for this would be to change the macro from Apple related to libc++ related, and having a comment explaining what's going on.

[MichaelSB]

I was busy with other things myself, so I had close to no time to dig deeper. For me this looks like: wvalue contains std::unique_ptrs. The code in question does assignments from wvalues. So the wvalues should be moved not copied. I don't see a move in the code in question. What am I missing?

[The-EDev]

Well the code in question does assignments from initializer_lists and objects. You might be correct in that the lists would need to be moved, but the objects already have an rvalue assignment operator that does the moving, for a normal lvalue assignment the data needs to be copied, the reason the macros are there is because I didn't want to construct a new object when I could use the existing object's assignment operator. I hope that made sense..