For bootstrapping purposes, this commit does not remove all uses of
the keyword "pure" -- doing so would cause the compiler to no longer
bootstrap due to some syntax extensions ("deriving" in particular).
Instead, it makes the compiler ignore "pure". Post-snapshot, we can
remove "pure" from the language.
There are quite a few (~100) borrow check errors that were essentially
all the result of mutable fields or partial borrows of `@mut`. Per
discussions with Niko I think we want to allow partial borrows of
`@mut` but detect obvious footguns. We should also improve the error
message when `@mut` is erroneously reborrowed.
This removes most explicit uses of the + argument mode. Pending a
snapshot, I had to remove the forbid(deprecated_modes) pragma from
a bunch of files. I'll put it back!
+ mode still has to be used in a few places for functions that get
moved (see task.rs)
The changes outside core and std are due to the to_bytes trait and
making the compiler (with legacy modes on) agree with the libraries
(with legacy modes off) about modes.
The Mut<T> type is intended to allow freezable data stuctures to be stored in
`@mut` boxes. Currently this causes borrowck to be very conserivative since it
cannot prove that you are not modifying such a structure while iterating over
it, for example. But if you do `@Mut<T>` instead of `@mut T`, you will
effectively convert borrowck's static checks into dynamic ones. This lets
you use the e.g. send_map just like a Java Map or something else.
