Tracking bug for RFC 18 - undefined struct layout

[brson]

rust-lang/rfcs#79

Nominating.

[pcwalton]

What exactly is the action needed here? Add the lint, or something else?

[pnkfelix]

Action items:

• add a lint,
• change any docs that say struct layout is defined by default,
• ensure we have support for repr(c) attribute on structs

[pnkfelix]

P-backcompat-lang, 1.0.

[emberian]

Taking this. I'll add a lint for using non-#[repr(C)] structs in FFI, transitively, as well as adding a separate codepath through trans that makes sure such structs have a C-compatible ABI.

[lilyball]

Due to the dead_code lint now changing behavior in the presence of #[repr(C)], I'd really like to see the FFI lint done sooner rather than later, even if nothing else is done yet.