Remove some feature gates
The first commit removes various feature gates that are unused. The second commit replaces some `Fn` implementations with `Iterator` implementations, which is much cleaner IMO. The third commit replaces an unboxed_closures feature gate with min_specialization. For some reason the unboxed_closures feature gate suppresses the min_specialization feature gate from triggering on an `TrustedStep` impl. The last comment just turns a regular comment into a doc comment as drive by cleanup. I can move it to a separate PR if preferred.
Make diangostic item naming consistent
Right now there is about a 50/50 split of naming diagnostic items as `vec_type` vs `Vec`. So it is hard to guess a diagnostic item name with confidence. I know it's not great to change these retroactively, but I think it will be much easier to maintain consistency after consistency is established.
Make *const (), *mut () okay for FFI
Pointer-to-() is used occasionally in the standard library to mean "pointer to none-of-your-business". Examples:
- `RawWakerVTable::new` https://doc.rust-lang.org/1.51.0/std/task/struct.RawWakerVTable.html#method.new
- `<*const T>::to_raw_parts` https://doc.rust-lang.org/nightly/std/primitive.pointer.html#method.to_raw_parts
I believe it's useful for the same purpose in FFI signatures, even while `()` itself is not FFI safe. The following should be allowed:
```rust
extern "C" {
fn demo(pc: *const (), pm: *mut ());
}
```
Prior to this PR, those pointers were not considered okay for an extern signature.
```console
warning: `extern` block uses type `()`, which is not FFI-safe
--> src/main.rs:2:17
|
2 | fn demo(pc: *const (), pm: *mut ());
| ^^^^^^^^^ not FFI-safe
|
= note: `#[warn(improper_ctypes)]` on by default
= help: consider using a struct instead
= note: tuples have unspecified layout
warning: `extern` block uses type `()`, which is not FFI-safe
--> src/main.rs:2:32
|
2 | fn demo(pc: *const (), pm: *mut ());
| ^^^^^^^ not FFI-safe
|
= help: consider using a struct instead
= note: tuples have unspecified layout
```
Implement `#[must_not_suspend]`
implements #83310
Some notes on the impl:
1. The code that searches for the attribute on the ADT is basically copied from the `must_use` lint. It's not shared, as the logic did diverge
2. The RFC does specify that the attribute can be placed on fn's (and fn-like objects), like `must_use`. I think this is a direct copy from the `must_use` reference definition. This implementation does NOT support this, as I felt that ADT's (+ `impl Trait` + `dyn Trait`) cover the usecase's people actually want on the RFC, and adding an imp for the fn call case would be significantly harder. The `must_use` impl can do a single check at fn call stmt time, but `must_not_suspend` would need to answer the question: "for some value X with type T, find any fn call that COULD have produced this value". That would require significant changes to `generator_interior.rs`, and I would need mentorship on that. `@eholk` and I are discussing it.
3. `@estebank` do you know a way I can make the user-provided `reason` note pop out? right now it seems quite hidden
Also, I am not sure if we should run perf on this
r? `@nikomatsakis`
This also adjusts the lint docs generation to accept (and ignore) an allow
attribute, rather than expecting the documentation to be immediately followed by
the lint name.
Gather module items after lowering.
This avoids having a non-local analysis inside lowering.
By implementing `hir_module_items` using a visitor, we make sure that iterations and visitors are consistent.
Fix ICE in `improper_ctypes_definitions` lint with all-ZST transparent types
Fixes#87496. There is also another function in the same file that looks fishy, but I haven't been able to produce an ICE there, and in any case, it's not related to #87496:
fd853c00e2/compiler/rustc_lint/src/types.rs (L720-L734)
r? ```@JohnTitor```
Const drop
The changes are pretty primitive at this point. But at least it works. ^-^
Problems with the current change that I can think of now:
- [x] `~const Drop` shouldn't change anything in the non-const world.
- [x] types that do not have drop glues shouldn't fail to satisfy `~const Drop` in const contexts. `struct S { a: u8, b: u16 }` This might not fail for `needs_non_const_drop`, but it will fail in `rustc_trait_selection`.
- [x] The current change accepts types that have `const Drop` impls but have non-const `Drop` glue.
Fixes#88424.
Significant Changes:
- `~const Drop` is no longer treated as a normal trait bound. In non-const contexts, this bound has no effect, but in const contexts, this restricts the input type and all of its transitive fields to either a) have a `const Drop` impl or b) can be trivially dropped (i.e. no drop glue)
- `T: ~const Drop` will not be linted like `T: Drop`.
- Instead of recursing and iterating through the type in `rustc_mir::transform::check_consts`, we use the trait system to special case `~const Drop`. See [`rustc_trait_selection::...::candidate_assembly#assemble_const_drop_candidates`](https://github.com/fee1-dead/rust/blob/const-drop/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs#L817) and others.
Changes not related to `const Drop`ping and/or changes that are insignificant:
- `Node.constness_for_typeck` no longer returns `hir::Constness::Const` for type aliases in traits. This was previously used to hack how we determine default bound constness for items. But because we now use an explicit opt-in, it is no longer needed.
- Removed `is_const_impl_raw` query. We have `impl_constness`, and the only existing use of that query uses `HirId`, which means we can just operate it with hir.
- `ty::Destructor` now has a field `constness`, which represents the constness of the destructor.
r? `@oli-obk`
Avoid invoking the hir_crate query to traverse the HIR
Walking the HIR tree is done using the `hir_crate` query. However, this is unnecessary, since `hir_owner(CRATE_DEF_ID)` provides the same information. Since depending on `hir_crate` forces dependents to always be executed, this leads to unnecessary work.
By splitting HIR and attributes visits, we can avoid an edge to `hir_crate` when trying to visit the HIR tree.
Provide `layout_of` automatically (given tcx + param_env + error handling).
After #88337, there's no longer any uses of `LayoutOf` within `rustc_target` itself, so I realized I could move the trait to `rustc_middle::ty::layout` and redesign it a bit.
This is similar to #88338 (and supersedes it), but at no ergonomic loss, since there's no funky `C: LayoutOf<Ty = Ty>` -> `Ty: TyAbiInterface<C>` generic `impl` chain, and each `LayoutOf` still corresponds to one `impl` (of `LayoutOfHelpers`) for the specific context.
After this PR, this is what's needed to get `trait LayoutOf` (with the `layout_of` method) implemented on some context type:
* `TyCtxt`, via `HasTyCtxt`
* `ParamEnv`, via `HasParamEnv`
* a way to transform `LayoutError`s into the desired error type
* an error type of `!` can be paired with having `cx.layout_of(...)` return `TyAndLayout` *without* `Result<...>` around it, such as used by codegen
* this is done through a new `LayoutOfHelpers` trait (and so is specifying the type of `cx.layout_of(...)`)
When going through this path (and not bypassing it with a manual `impl` of `LayoutOf`), the end result is that only the error case can be customized, the query itself and the success paths are guaranteed to be uniform.
(**EDIT**: just noticed that because of the supertrait relationship, you cannot actually implement `LayoutOf` yourself, the blanket `impl` fully covers all possible context types that could ever implement it)
Part of the motivation for this shape of API is that I've been working on querifying `FnAbi::of_*`, and what I want/need to introduce for that looks a lot like the setup in this PR - in particular, it's harder to express the `FnAbi` methods in `rustc_target`, since they're much more tied to `rustc` concepts.
r? `@nagisa` cc `@oli-obk` `@bjorn3`
Introduce `let...else`
Tracking issue: #87335
The trickiest part for me was enforcing the diverging else block with clear diagnostics. Perhaps the obvious solution is to expand to `let _: ! = ..`, but I decided against this because, when a "mismatched type" error is found in typeck, there is no way to trace where in the HIR the expected type originated, AFAICT. In order to pass down this information, I believe we should introduce `Expectation::LetElseNever(HirId)` or maybe add `HirId` to `Expectation::HasType`, but I left that as a future enhancement. For now, I simply assert that the block is `!` with a custom `ObligationCauseCode`, and I think this is clear enough, at least to start. The downside here is that the error points at the entire block rather than the specific expression with the wrong type. I left a todo to this effect.
Overall, I believe this PR is feature-complete with regard to the RFC.
Warn when [T; N].into_iter() is ambiguous in the new edition.
Fixes https://github.com/rust-lang/rust/issues/88475
In https://github.com/rust-lang/rust/issues/88475, a situation was found where `[T; N].into_iter()` becomes *ambiguous* in the new edition. This is different than the case where `(&[T; N]).into_iter()` resolves differently, which was the only case handled by the `array_into_iter` lint. This is almost identical to the new-traits-in-the-prelude problem. Effectively, due to the array-into-iter hack disappearing in Rust 2021, we effectively added `IntoIterator` to the 'prelude' in Rust 2021 specifically for arrays.
This modifies the prelude collisions lint to detect that case and emit a `array_into_iter` lint in that case.
rustc_target: `TyAndLayout::field` should never error.
This refactor (making `TyAndLayout::field` return `TyAndLayout` without any `Result` around it) is based on a simple observation, regarding `TyAndLayout::field`:
If `cx.layout_of(ty)` succeeds (for some `cx` and `ty`), then `.field(cx, i)` on the resulting `TyAndLayout` should *always* succeed in computing `cx.layout_of(field_ty)` (where `field_ty` is the type of the `i`th field of `ty`).
The reason for this is that no matter which field is chosen, `cx.layout_of(field_ty)` *will have already been computed*, as part of computing `cx.layout_of(ty)`, as we cannot determine the layout of *any* type without considering the layouts of *all* of its fields.
And so it should be fine to turn any errors into ICEs, since they likely indicate a `cx` mismatch, or some other edge case that is due to a compiler bug (as opposed to ever being an user-facing error).
<hr/>
Each commit should probably be reviewed separately, though note that there's some `where` clauses (in `rustc_target::abi::call::*`) that change in most commits.
cc `@nagisa` `@oli-obk`
