Remove restriction on isize/usize in repr(simd)
As discussed in #55078, there's no known reason for this restriction.
It's unlikely that repr(simd) will be stabilized in its current form, but
might as well remove some restrictions on it.
This removes the branch in `is_machine` which returns false for these types.
`is_machine` is only used for the repr(simd) type validation check.
Add `-Z allow_features=...` flag
Adds a compiler option to allow only whitelisted features.
For projects on nightly that want to prevent feature-creep (and maybe, someday, move off of nightly). Not being able to enforce this has been a problem on Fuchsia and at other big companies.
This doesn't support filtering edition feature flags, but someone is welcome to add that if they need it.
As discussed in #55078, there's no known reason for this restriction.
It's unlikely that repr(simd) will be stabilized in its current form, but
might as well remove some restrictions on it.
This removes the branch in `is_machine` which returns false for these types.
`is_machine` is only used for the repr(simd) type validation check.
resolve: Simplify import resolution for mixed 2015/2018 edition mode
Non-controversial part of https://github.com/rust-lang/rust/pull/57745.
Before:
| Local edition (per-span) | Global edition (--edition) | Imports (`use foo;`) | Absolute paths (`::foo`) |
| ------------- |----------------|-----------------------------------------|------------------------------------------------|
| 2018 | Any | Uniform | Extern prelude |
| 2015 | 2015 | Crate-relative | Crate-relative |
| 2015 | 2018 | Crate-relative with fallback to Uniform (future-proofed to error if the result is not Crate-relative or from Extern prelude) | Crate-relative with fallback to Extern prelude |
After:
| Local edition (per-span) | Global edition (--edition) | Imports (`use foo;`) | Absolute paths (`::foo`) |
| ------------- |----------------|-----------------------------------------|------------------------------------------------|
| 2018 | Any | Uniform | Extern prelude |
| 2015 | 2015 | Crate-relative | Crate-relative |
| 2015 | 2018 | Crate-relative with fallback to Extern prelude | Crate-relative with fallback to Extern prelude |
I.e. only the behavior of the mixed local-2015-global-2018 mode is changed.
This mixed mode has two goals:
- Address regressions from https://github.com/rust-lang/rust/pull/56053#issuecomment-440826397.
Both "before" and "after" variants address those regressions.
- Be retrofit-able to "full 2015" edition (https://github.com/rust-lang/rust/pull/57745).
Any more complex fallback scheme (with more candidates) than "Crate-relative with fallback to Extern prelude" will give more regressions than https://github.com/rust-lang/rust/pull/57745#issuecomment-455855089 and is therefore less retrofit-able while also being, well, more complex.
So, we can settle on "Crate-relative with fallback to Extern prelude".
(I'll hopefully proceed with https://github.com/rust-lang/rust/pull/57745 after mid-February.)
r? @Centril
ignore higher-ranked object bound conditions created by WF
In the `issue-53548` test added in this PR, the `Box<dyn Trait>` type is expanded to `Box<dyn Trait + 'static>`, but the generator "witness" that results is `for<'r> { Box<dyn Trait + 'r> }`. The WF code was encountering an ICE (when debug-assertions were enabled) and an unexpected compilation error (without debug-asserions) when trying to process this `'r` region bound. In particular, to be WF, the region bound must meet the requirements of the trait, and hence we got `for<'r> { 'r: 'static }`. This would ICE because the `Binder` constructor we were using was assering that no higher-ranked regions were involved (because the WF code is supposed to skip those). The error (if debug-asserions were disabled) came because we obviously cannot prove that `'r: 'static` for any region `'r`. Pursuant with
our "lazy WF" strategy for higher-ranked regions, the fix is not to require that `for<'r> { 'r: 'static }` holds (this is also analogous to what we would do for higher-ranked regions appearing within the trait in other positions).
Fixes#53548
r? @pnkfelix
Fix#54822 and associated faulty tests
Type checking associated constants can require trait bounds, but an empty
parameter environment was provided to the trait solver. Providing an
appropriate parameter environment seems to fix#54822 and also make one of the
cases in src/test/ui/nll/trait-associated-constant.rs that should compile
successfully do so. It also (slightly) improves the error message in
src/test/ui/associated-const/associated-const-generic-obligations.rs
