Implement Fuse with Option
The former `done` flag was roughly similar to an `Option` tag, but left
the possibity of misuse. By using a real `Option`, we can set `None`
when the iterator is exhausted, removing any way to call it again. We
also allow niche layout this way, so the `Fuse` may be smaller.
The `FusedIterator` specialization does want to ignore the possibility
of exhaustion though, so it uses `unsafe { intrinsics::unreachable() }`
to optimize that branch away. The entire `Fuse` implementation is now
isolated in its own module to contain that unsafety.
r? @scottmcm
use checked casts and arithmetic in Miri engine
This is unfortunately pretty annoying because we have to cast back and forth between `u64` and `usize` more often that should be necessary, and that cast is considered fallible.
For example, should [this](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/mir/interpret/value/enum.ConstValue.html) really be `usize`?
Also, `LayoutDetails` uses `usize` for field indices, but in Miri we use `u64` to be able to also handle array indexing. Maybe methods like `mplace_field` should be suitably generalized to accept both `u64` and `usize`?
r? @oli-obk Cc @eddyb
Fix smaller issues with invalid placeholder type errors
Follow up to #70294.
- Fix placement of suggested generic param when bounds are present.
- Reduce error duplication for invalid placeholder types in `fn` types.
r? @Centril
resolve: Remove `rustc_attrs` as a standalone feature gate
Now it only gates specific built-in attributes.
So if you want to make a rustc attribute, make it a built-in (this was already the case in practice for some time).
Update backtrace crate to 0.3.46
* Support line-tables-only when using libbacktrace
* Update libbacktrace to latest master
* Define HAVE_KERN_PROC on FreeBSD to fixrust-lang/rust#54434
Request "-Z unstable-options" for unstable options
Explicitly requests the "-Z unstable-options" flag if someone attempts to use
a cargo option gated by it. This enhances discoverability, particularly in the
instance where the user is on the nightly compiler but isn't using the flag.
This relates to, but does not end with or resolve, issue #65770.
Miri: move ModifiedStatic to ConstEval errors
Also generally adjust terminology from "static" to "global" where appropriate (to avoid confusion with specifically `static` items).
The former `done` flag was roughly similar to an `Option` tag, but left
the possibity of misuse. By using a real `Option`, we can set `None`
when the iterator is exhausted, removing any way to call it again. We
also allow niche layout this way, so the `Fuse` may be smaller.
The `FusedIterator` specialization does want to ignore the possibility
of exhaustion though, so it uses `unsafe { intrinsics::unreachable() }`
to optimize that branch away. The entire `Fuse` implementation is now
isolated in its own module to contain that unsafety.
