Please specify minimum Rust version (and add reference to rustup)

[codethief]

When running cargo build --release on the latest snapshot from the git repository on a machine with Ubuntu 17.10 freshly installed I end up with the following error message:

$ cargo build --release
[…]
   Compiling bitflags v1.0.0
error: associated constants are experimental (see issue #29646)
   --> ~/.cargo/registry/src/github.com-1ecc6299db9ec823/bitflags-1.0.0/src/lib.rs:441:17
    |
441 |                   pub const $Flag: $BitFlags = $BitFlags { bits: $value };
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    | 
   ::: ~/.cargo/registry/src/github.com-1ecc6299db9ec823/bitflags-1.0.0/src/example_generated.rs
    |
4   | / bitflags! {
5   | |     /// This is the same `Flags` struct defined in the [crate level example](../index.html#example).
6   | |     /// Note that this struct is just for documentation purposes only, it must not be used outside
7   | |     /// this crate.
...   |
15  | |     }
16  | | }
    | |_- in this macro invocation

error: associated constants are experimental (see issue #29646)
   --> ~/.cargo/registry/src/github.com-1ecc6299db9ec823/bitflags-1.0.0/src/lib.rs:441:17
    |
441 |                   pub const $Flag: $BitFlags = $BitFlags { bits: $value };
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    | 
   ::: ~/.cargo/registry/src/github.com-1ecc6299db9ec823/bitflags-1.0.0/src/example_generated.rs
    |
4   | / bitflags! {
5   | |     /// This is the same `Flags` struct defined in the [crate level example](../index.html#example).
6   | |     /// Note that this struct is just for documentation purposes only, it must not be used outside
7   | |     /// this crate.
...   |
15  | |     }
16  | | }
    | |_- in this macro invocation

error: associated constants are experimental (see issue #29646)
   --> ~/.cargo/registry/src/github.com-1ecc6299db9ec823/bitflags-1.0.0/src/lib.rs:441:17
    |
441 |                   pub const $Flag: $BitFlags = $BitFlags { bits: $value };
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    | 
   ::: ~/.cargo/registry/src/github.com-1ecc6299db9ec823/bitflags-1.0.0/src/example_generated.rs
    |
4   | / bitflags! {
5   | |     /// This is the same `Flags` struct defined in the [crate level example](../index.html#example).
6   | |     /// Note that this struct is just for documentation purposes only, it must not be used outside
7   | |     /// this crate.
...   |
15  | |     }
16  | | }
    | |_- in this macro invocation

error: associated constants are experimental (see issue #29646)
   --> ~/.cargo/registry/src/github.com-1ecc6299db9ec823/bitflags-1.0.0/src/lib.rs:441:17
    |
441 |                   pub const $Flag: $BitFlags = $BitFlags { bits: $value };
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    | 
   ::: ~/.cargo/registry/src/github.com-1ecc6299db9ec823/bitflags-1.0.0/src/example_generated.rs
    |
4   | / bitflags! {
5   | |     /// This is the same `Flags` struct defined in the [crate level example](../index.html#example).
6   | |     /// Note that this struct is just for documentation purposes only, it must not be used outside
7   | |     /// this crate.
...   |
15  | |     }
16  | | }
    | |_- in this macro invocation

error: aborting due to 4 previous errors

error: Could not compile `bitflags`.
Build failed, waiting for other jobs to finish...
error: build failed

According to this issue I need at least Rust version 1.20 to fix this which is not yet available in the official Ubuntu repositories. It seems this can be fixed by installing Rust through rustup which, I suppose, most Rust developers are familiar with. However, as I'm not intimately familiar with the Rust tool chain I didn't expect I'd have to avoid the official Ubuntu repositories. I (and probably other users in a similar situation) would therefore appreciate it if you could add a comment to the README, mentioning the required Rust version and how to obtain it. :)

[greshake]

I've added a notice to the README mentioning that we only test compatibility with the latest stable Rust version. I really don't want to get into maintaining backwards compatibility with distros that like to ship old versions of everything. There is a simple and officially recommended way to install Rust and that is rustup. If someone still really wants to use an outdated compiler, I'm not going to maintain a Wiki on how to do that. It's probably nonsense to try anyway. If we start to keep track of which distro ships which compiler version by default and how to compile with that or obtain some usable version, we might as well open a new project for that.

[greshake]

Fixed in 485d5b4

[codethief]

Thanks, that's exactly what I had in mind!