Fix ioctl() call compilation error for freebsd

[gchers]

This is a temporary fix to rust-lang/libc#704 and fixes #12.

May want to remove when rust libc accepts rust-lang/libc#704.

[murarth]

A couple minor points: I believe attributes on expressions landed in stable rustc only a few days ago, so I think it would be better to implement this as cfg-marked functions, to continue supporting the old stable. Also, I think the cast would be better done as as c_ulong.

[gchers]

Hi, this should solve with backward compatibility.

NOTE_1: I wasn't sure how to create a more generic ioctl() wrapper (i.e., one that could accept either c_int or c_ulong for argument request, which is the case for non-freebsd platforms), so I simply created a wrapper for the call to ioctl() with request=TIOCGWINSZ.

NOTE_2:
Just in case, I post here for reference, in order:
platform, TIOCGWINSZ type, ioctl() request type
for the current libc, and mark with * the wrong entries.
I omit openbsd -like entries for which TIOCGWINSZ is not defined; I suspect linefeed doesn't support them anyway.

linux:
mips-unknown-linux-gnu, c_ulong, c_ulong
arm-unknown-linux-gnueabihf, c_ulong, c_ulong
i686-unknown-linux-gnu, c_ulong, c_ulong
x86_64-unknown-linux-gnu, c_ulong, c_ulong
aarch64-unknown-linux-gnu, c_ulong, c_ulong
x86_64-unknown-linux-musl, c_int, c_int

linux-android:
arm-linux-androideabi, c_int, c_int

freebsd:
* x86_64-unknown-freebsd, c_uint, c_ulong
* x86_64-unknown-dragonfly, c_uint, c_ulong

apple:
x86_64-apple-darwin, c_ulong, c_ulong
i686-apple-darwin, c_ulong, c_ulong

other:
asmjs-unknown-emscripten, c_int, c_int
wasm32-unknown-emscripten, c_int, c_int
sparc64-unknown-linux-gnu, c_ulong, c_ulong

[murarth]

This generates an unused_imports warning on non-freebsd platforms. You can instead add use libc::c_ulong; inside the freebsd version of ioctl_wrapper.

[murarth]

If dragonfly has the same issue, you can go ahead and apply this fix for dragonfly, as well.

I'd like to support any platform that can reasonably be supported. Do you know whether it is a bug that libc doesn't define TIOCGWINSZ for OpenBSD or does OpenBSD truly not implement this ioctl request?

[murarth]

I've just realized something that will greatly simplify the implementation of this fix: For each integer type in Rust, there exist From implementations to convert losslessly from each smaller integer type of the same signedness, e.g. from u32 to u64. So, the only change that needs to be made to the original code is to pass TIOCGWINSZ.into() to ioctl. (Though you can preserve the comment about the FreeBSD/Dragonfly issue that explains why this is necessary.)

Because a From implementation also exists to convert a value of any type into itself, TIOCGWINSZ.into() can be used on all platforms (provided that the signedness matches for the type of the constant TIOCGWINSZ and the type expected by ioctl, which does appear to be the case).

[gchers]

Such an elegant solution! Sweet, I was really hoping there was something like that.

As for your openbsd question. TIOCGWINSZ is defined, but not in rust libc [1].
I'll: i) try compiling linefeed on an openbsd tomorrow (which I suspect will fail), ii) look for its actual value in ioctl.h (it may be different from the one in freebsd).

[1] https://man.openbsd.org/tty.4#TIOCGWINSZ

[murarth]

Looks good. Go ahead and squash the commits and I'll merge it.