Document canonicalization in `std::env::current_dir`

[AZMCode]

As of now, the stable and nightly documentation on std::env::current_dir only states

Returns the current working directory as a PathBuf.

And proceeds to note a couple of errors the function may fail with.
This does not mention the fact that (as far as I am aware, testing on Linux) the path is also canonicalized, having resolved all symlinks in any segment of the path. I'd imagine not documenting this behavior could lead to confusion and/or bugs, if it already hasn't.

I tried this code within a symlink folder /example/symlink/here pointing to /symlink/target/here:

println!("{:#?}",std::env::current_dir().unwrap())

I expected to see get the output: "/example/symlink/here"
Instead, this was output: "/symlink/target/here"

Currently using the nightly compiler.

For obvious reasons, there's no backtrace.

Update: Read a bit through the code and realized this behavior might be libc-dependent
ldd --version on my system returns ldd (GNU libc) 2.33

[hkratz]

For UNIX Rust just calls getcwd() and that behavior is documented in the POSIX spec, so it will be the same on all conforming implementations. We should document which platform-specific function we call here just like we do with other filesystem functions (e.g. here).

@rustbot label T-libs A-docs

[GuillaumeGomez]

It was also missing for set_current_dir so I opened #93635 for both.

[AZMCode]

Thanks a lot