File does not implement Debug

[steveklabnik]

All types should, but it doesn't:

the trait `core::fmt::Debug` is not implemented for the type `std::fs::File` [E0277]

[sfackler]

We can easily slap one on that just prints the file descriptor/HANDLE, but it would ideally include the path of the open file. It looks like it'll be a bit of a pain to get.

Windows can get it via either GetFinalPathNameByHandle or GetFileInformationByHandleEx. It does look like both of those require Vista, but this page has a workaround for earlier versions of Windows: https://msdn.microsoft.com/en-us/library/windows/desktop/aa366789%28v=vs.85%29.aspx.

OSX can grab it by passing F_GETPATH to fnctl: https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man2/fcntl.2.html.

Looks like Linux may have to poke around in /proc/pid/fds/ unfortunately.

[sfackler]

It'd also be nice to print if the file's writable or read only.

[lambda-fairy]

On Linux, you can read the link at /proc/self/fd/<FD>. The destination of that symlink is the name of the file.

That shouldn't be too hard, given that we have a read_link function in std.

[lambda-fairy]

I'm working on this.

[nagisa]

Relying on procfs is bad, because it might not be mounted or be mounted at a non-standard location.

[lambda-fairy]

@nagisa We aren't really relying on it here. If /proc isn't present, the code would just not print a path. No biggie.

[lambda-fairy]

Currently the Debug impl gives path and access mode information on Linux only.

If anyone wants to flesh out the Windows or OS X or BSD code, then feel free.

[steveklabnik]

use std::fs::File;

fn main() {
    let f = File::open("hello.rs");
    println!("{:?}", f);
}

prints

Ok(File { fd: 3, path: "/home/steve/tmp/hello.rs", read: true, write: false })

[Eh2406]

There is a FIXME related to this issue,
https://github.com/rust-lang/rust/blob/master/src/libstd/sys/windows/fs.rs#L445
https://github.com/rust-lang/rust/blob/master/src/libstd/sys/unix/fs.rs#L592
https://github.com/rust-lang/rust/blob/master/src/libstd/sys/unix/fs.rs#L612
Now that the issue is closed can the FIXME be fix, or made more specific?