rust-lang/rust — pull request #17501 by pcwalton (2014-09-24 06:02:32+00:00)
Title: librustc: Fix up mutability in method autoderefs if incorrect, and

prefer `Deref` over `DerefMut` in all other circumstances.

Because the compiler now prefers `Deref`, this can break code that
looked like:

let mut foo = bar.borrow_mut();
(*foo).call_something_that_requires_mutable_self();

Replace this code with:

let mut foo = bar.baz();
(&mut *foo).call_something_that_requires_mutable_self();

Closes #12825.

[breaking-change]

r? @nikomatsakis