std::os::errno returns a different type than IoError::from_errno takes

[tomjakubowski]

std::os::errno returns an int whereas IoError::from_errno takes a uint. It's a bit irritating to have to write out errno() as uint every time one constructs an IoError from errno.

AIUI errno in C is always of (C) type int, so my inclination would be to change from_errno unless there's a good reason for it to be using uint.

[mahkoh]

errno should return c_int.

[tomjakubowski]

On Windows std::os::errno returns a uint: https://github.com/rust-lang/rust/blob/master/src/libstd/os.rs#L944-L957

This means that IoError::from_errno(errno(), ...) compiles on Windows without a cast but not on other platforms.

[steveklabnik]

src/libstd/os.rs:pub fn errno() -> uint {
src/libstd/sys/unix/os.rs:pub fn errno() -> int {
src/libstd/sys/unix/os.rs:    fn errno_location() -> *const c_int {
src/libstd/sys/unix/os.rs:    fn errno_location() -> *const c_int {
src/libstd/sys/unix/os.rs:    fn errno_location() -> *const c_int {
src/libsrc/libstd/os.rs:pub fn errno() -> uint {

[steveklabnik]

/cc @aturon , is this a backcompati issue?

[aturon]

This affects the stabilization of the new std::io::Error::from_os_error. Nominating for 1.0-beta P-backcompat-libs.

[pnkfelix]

I-needs-decision, P-high; but not 1.0 beta nor P-backcompat-libs.

(We may need to put more thought into how we track such things)

[huonw]

We no longer have std::os:errno, just various methods on io::Error, which all use i32. Closing.