This removes all remnants of `@` pointers from rustc. Additionally, this removes
the `GC` structure from the prelude as it seems odd exporting an experimental
type in the prelude by default.
Closes#14193
[breaking-change]
This PR enables the use of mutable slices in *mutable* static items. The work was started by @xales and I added a follow-up commit that moves the *immutable* restriction to the recently added `check_static`
Closes#11411
- For each *mutable* static item, check that the **type**:
- cannot own any value whose type has a dtor
- cannot own any values whose type is an owned pointer
- For each *immutable* static item, check that the **value**:
- does not contain any ~ or box expressions
(including ~[1, 2, 3] sort of things)
- does not contain a struct literal or call to an enum
variant / struct constructor where
- the type of the struct/enum has a dtor
