Merge unboxed trait object error suggestion into regular dyn incompat error
Another hir-walker removed from the well-formed queries. This error was always a duplicate of another, but it was able to provide more information because it could invoke `is_dyn_compatible` without worrying about cycle errors. That's also the reason we can't put the error directly into hir_ty_lowering when lowering a `dyn Trait` within an associated item signature. So instead I packed it into the error handling of wf obligation checking.
Prefer built-in sized impls (and only sized impls) for rigid types always
This PR changes the confirmation of `Sized` obligations to unconditionally prefer the built-in impl, even if it has nested obligations. This also changes all other built-in impls (namely, `Copy`/`Clone`/`DiscriminantKind`/`Pointee`) to *not* prefer built-in impls over param-env impls. This aligns the old solver with the behavior of the new solver.
---
In the old solver, we register many builtin candidates with the `BuiltinCandidate { has_nested: bool }` candidate kind. The precedence this candidate takes over other candidates is based on the `has_nested` field. We only prefer builtin impls over param-env candidates if `has_nested` is `false`
2b4694a698/compiler/rustc_trait_selection/src/traits/select/mod.rs (L1804-L1866)
Preferring param-env candidates when the builtin candidate has nested obligations *still* ends up leading to detrimental inference guidance, like:
```rust
fn hello<T>() where (T,): Sized {
let x: (_,) = Default::default();
// ^^ The `Sized` obligation on the variable infers `_ = T`.
let x: (i32,) = x;
// We error here, both a type mismatch and also b/c `T: Default` doesn't hold.
}
```
Therefore this PR adjusts the candidate precedence of `Sized` obligations by making them a distinct candidate kind and unconditionally preferring them over all other candidate kinds.
Special-casing `Sized` this way is necessary as there are a lot of traits with a `Sized` super-trait bound, so a `&'a str: From<T>` where-bound results in an elaborated `&'a str: Sized` bound. People tend to not add explicit where-clauses which overlap with builtin impls, so this tends to not be an issue for other traits.
We don't know of any tests/crates which need preference for other builtin traits. As this causes builtin impls to diverge from user-written impls we would like to minimize the affected traits. Otherwise e.g. moving impls for tuples to std by using variadic generics would be a breaking change. For other builtin impls it's also easier for the preference of builtin impls over where-bounds to result in issues.
---
There are two ways preferring builtin impls over where-bounds can be incorrect and undesirable:
- applying the builtin impl results in undesirable region constraints. E.g. if only `MyType<'static>` implements `Copy` then a goal like `(MyType<'a>,): Copy` would require `'a == 'static` so we must not prefer it over a `(MyType<'a>,): Copy` where-bound
- this is mostly not an issue for `Sized` as all `Sized` impls are builtin and don't add any region constraints not already required for the type to be well-formed
- however, even with `Sized` this is still an issue if a nested goal also gets proven via a where-bound: [playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=30377da5b8a88f654884ab4ebc72f52b)
- if the builtin impl has associated types, we should not prefer it over where-bounds when normalizing that associated type. This can result in normalization adding more region constraints than just proving trait bounds. https://github.com/rust-lang/rust/issues/133044
- not an issue for `Sized` as it doesn't have associated types.
r? lcnr
Continuing the work from #137350.
Removes the unused methods: `expect_variant`, `expect_field`,
`expect_foreign_item`.
Every method gains a `hir_` prefix.
Use `edition = "2024"` in the compiler (redux)
Most of this is binding mode changes, which I fixed by running `x.py fix`.
Also adds some miscellaneous `unsafe` blocks for new unsafe standard library functions (the setenv ones), and a missing `unsafe extern` block in some enzyme codegen code, and fixes some precise capturing lifetime changes (but only when they led to errors).
cc ``@ehuss`` ``@traviscross``
Prune dead regionck code
We never encounter `ObligationCauseCode`s that correspond to region obligations that originate from "within" a body, since we don't do HIR regionck anymore on bodies. So prune some dead code.
tree-wide: parallel: Fully removed all `Lrc`, replaced with `Arc`
tree-wide: parallel: Fully removed all `Lrc`, replaced with `Arc`
This is continuation of https://github.com/rust-lang/rust/pull/132282 .
I'm pretty sure I did everything right. In particular, I searched all occurrences of `Lrc` in submodules and made sure that they don't need replacement.
There are other possibilities, through.
We can define `enum Lrc<T> { Rc(Rc<T>), Arc(Arc<T>) }`. Or we can make `Lrc` a union and on every clone we can read from special thread-local variable. Or we can add a generic parameter to `Lrc` and, yes, this parameter will be everywhere across all codebase.
So, if you think we should take some alternative approach, then don't merge this PR. But if it is decided to stick with `Arc`, then, please, merge.
cc "Parallel Rustc Front-end" ( https://github.com/rust-lang/rust/issues/113349 )
r? SparrowLii
`@rustbot` label WG-compiler-parallel
We have four macros for generating trivial traversal (fold/visit) and
lift impls.
- `rustc_ir::TrivialTypeTraversalImpls`
- `rustc_middle::TrivialTypeTraversalImpls`
- `rustc_middle::TrivialLiftImpls`
- `rustc_middle::TrivialTypeTraversalAndLiftImpls`
The first two are very similar. The last one just combines the second
and third one.
The macros themselves are ok, but their use is a mess. This commit does
the following.
- Removes types that no longer need a lift and/or traversal impl from
the macro calls.
- Consolidates the macro calls into the smallest number of calls
possible, with each one mentioning as many types as possible.
- Orders the types within those macro calls alphabetically, and makes
the module qualification more consistent.
- Eliminates `rustc_middle::mir::type_foldable`, because the macro calls
were merged and the manual `TypeFoldable` impls are better placed in
`structural_impls.rs`, alongside all the other ones.
This makes the code more concise. Moving forward, it also makes it more
obvious where new types should be added.
`rustc_span::symbol` defines some things that are re-exported from
`rustc_span`, such as `Symbol` and `sym`. But it doesn't re-export some
closely related things such as `Ident` and `kw`. So you can do `use
rustc_span::{Symbol, sym}` but you have to do `use
rustc_span::symbol::{Ident, kw}`, which is inconsistent for no good
reason.
This commit re-exports `Ident`, `kw`, and `MacroRulesNormalizedIdent`,
and changes many `rustc_span::symbol::` qualifiers in `compiler/` to
`rustc_span::`. This is a 200+ net line of code reduction, mostly
because many files with two `use rustc_span` items can be reduced to
one.
In this new version of Arbitrary Self Types, we no longer use the Deref trait
exclusively when working out which self types are valid. Instead, we follow a
chain of Receiver traits. This enables methods to be called on smart pointer
types which fundamentally cannot support Deref (for instance because they are
wrappers for pointers that don't follow Rust's aliasing rules).
This includes:
* Changes to tests appropriately
* New tests for:
* The basics of the feature
* Ensuring lifetime elision works properly
* Generic Receivers
* A copy of the method subst test enhanced with Receiver
This is really the heart of the 'arbitrary self types v2' feature, and
is the most critical commit in the current PR.
Subsequent commits are focused on:
* Detecting "shadowing" problems, where a smart pointer type can hide
methods in the pointee.
* Diagnostics and cleanup.
Naming: in this commit, the "Autoderef" type is modified so that it no
longer solely focuses on the "Deref" trait, but can now consider the
"Receiver" trait instead. Should it be renamed, to something like
"TraitFollower"? This was considered, but rejected, because
* even in the Receiver case, it still considers built-in derefs
* the name Autoderef is short and snappy.
