libstd: io::fs::File::stat() need not to take &mut self.

The same goes for sys::fs::FileDesc::fstat() on Windows.

Signed-off-by: NODA, Kai <nodakai@gmail.com>
libstd: explicitly disallow io::fs::File to open a directory.

On *BSD systems, we can open(2) a directory and directly read(2) from
it due to an old tradition.  We should avoid doing so by explicitly
calling fstat(2) to check the type of the opened file.

Opening a directory as a module file can't always be avoided.
Even when there's no "path" attribute trick involved, there can always
be a *directory* named "my_module.rs".

Fix #12460

Signed-off-by: NODA, Kai <nodakai@gmail.com>
auto merge of #19303 : nodakai/rust/libsyntax-reject-dirs, r=alexcrichton

On *BSD systems, we can `open(2)` a directory and directly `read(2)` from it due to an old tradition.  We should avoid doing so by explicitly calling `fstat(2)` to check the type of the opened file.

Opening a directory as a module file can't always be avoided.  Even when there's no "path" attribute trick involved, there can always be a *directory* named `my_module.rs`.

Incidentally, remove unnecessary mutability of `&self` from `io::fs::File::stat()`.
librustc: Make `Copy` opt-in.

This change makes the compiler no longer infer whether types (structures
and enumerations) implement the `Copy` trait (and thus are implicitly
copyable). Rather, you must implement `Copy` yourself via `impl Copy for
MyType {}`.

A new warning has been added, `missing_copy_implementations`, to warn
you if a non-generic public type has been added that could have
implemented `Copy` but didn't.

This breaks code like:

    #[deriving(Show)]
    struct Point2D {
        x: int,
        y: int,
    }

    fn main() {
        let mypoint = Point2D {
            x: 1,
            y: 1,
        };
        let otherpoint = mypoint;
        println!("{}{}", mypoint, otherpoint);
    }

Change this code to:

    #[deriving(Show)]
    struct Point2D {
        x: int,
        y: int,
    }

    impl Copy for Point2D {}

    fn main() {
        let mypoint = Point2D {
            x: 1,
            y: 1,
        };
        let otherpoint = mypoint;
        println!("{}{}", mypoint, otherpoint);
    }

This is the backwards-incompatible part of #13231.

Part of RFC #3.

[breaking-change]