Remove comment about handling non-global where bounds with corresponding projection
This comment is no longer relevant since we only assemble rigid projections if no param-env candidates hold.
Also remove a stray comment from the old solver.
r? lcnr
Fix replacing supertrait aliases in `ReplaceProjectionWith`
The new solver has a procedure called `predicates_for_object_candidate`, which elaborates the super-bounds and item-bounds that are required to hold for a dyn trait to implement something via a built-in object impl.
In that procedure, there is a folder called `ReplaceProjectionWith` which is responsible for replacing projections that reference `Self`, so that we don't encounter cycles when we then go on to normalize those projections in the process of proving these super-bounds.
That folder had a few problems: Firstly, it wasn't actually checking that this was a super bound originating from `Self`. Secondly, it only accounted for a *single* projection type def id, but trait objects can have multiple (i.e. `trait Foo<A, B>: Bar<A, Assoc = A> + Bar<B, Assoc = B>`).
To fix the first, it's simple enough to just add an equality check for the self ty. To fix the second, I implemented a matching step that's very similar to the `projection_may_match` check we have for upcasting, since on top of having multiple choices, we need to deal with both non-structural matches and ambiguity.
This probably lacks a bit of documentation, but I think it works pretty well.
Fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/171
r? lcnr
stepping into impls for normalization is unproductive
See the inline comment. This builds on the reasoning from #136824 (https://gist.github.com/lcnr/c49d887bbd34f5d05c36d1cf7a1bf5a5). Fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/176.
Looking at the end of the gist:
> The only ways to project out of a constructor are the following:
> - accessing an associated item, either its type or its item bounds
> - accessing super predicates
Detecting cases where we accessing the type of an associated item is easy, it's simply when we normalize. I don't yet know how to detect whether we step out of an impl by accessing item bounds. Once we also detect these cases we should be able to soundly support arbitrary coinductive traits. Luckily this does not matter for this PR :>
r? `@compiler-errors` cc `@nikomatsakis`
Rigidly project missing item due to guaranteed impossible sized predicate
This is a somewhat involved change, but it amounts to treating missing impl items due to guaranteed impossible where clauses (dyn/str/slice sized, cc #135480) as *rigid projections* rather than projecting to an error term, since that was preventing either reporting a proper error (in an empty param env) *or* successfully type checking the code (in the presence of trivially false where clauses).
Fixes https://github.com/rust-lang/rust/issues/138970
r? `@lcnr` `@oli-obk`
add `TypingMode::Borrowck`
Shares the first commit with #138499, doesn't really matter which PR to land first 😊😁
Introduces `TypingMode::Borrowck` which unlike `TypingMode::Analysis`, uses the hidden type computed by HIR typeck as the initial value of opaques instead of an unconstrained infer var. This is a part of https://github.com/rust-lang/types-team/issues/129.
Using this new `TypingMode` is unfortunately a breaking change for now, see tests/ui/impl-trait/non-defining-uses/as-projection-term.rs. Using an inference variable as the initial value results in non-defining uses in the defining scope. We therefore only enable it if with `-Znext-solver=globally` or `-Ztyping-mode-borrowck`
To do that the PR contains the following changes:
- `TypeckResults::concrete_opaque_type` are already mapped to the definition of the opaque type
- writeback now checks that the non-lifetime parameters of the opaque are universal
- for this, `fn check_opaque_type_parameter_valid` is moved from `rustc_borrowck` to `rustc_trait_selection`
- we add a new `query type_of_opaque_hir_typeck` which, using the same visitors as MIR typeck, attempts to merge the hidden types from HIR typeck from all defining scopes
- done by adding a `DefiningScopeKind` flag to toggle between using borrowck and HIR typeck
- the visitors stop checking that the MIR type matches the HIR type. This is trivial as the HIR type are now used as the initial hidden types of the opaque. This check is useful as a safeguard when not using `TypingMode::Borrowck`, but adding it to the new structure is annoying and it's not soundness critical, so I intend to not add it back.
- add a `TypingMode::Borrowck` which behaves just like `TypingMode::Analysis` except when normalizing opaque types
- it uses `type_of_opaque_hir_typeck(opaque)` as the initial value after replacing its regions with new inference vars
- it uses structural lookup in the new solver
fixes#112201, fixes#132335, fixes#137751
r? `@compiler-errors` `@oli-obk`
change definitely unproductive cycles to error
builds on top of #136824 by adding a third variant to `PathKind` for paths which may change to be coinductive in the future but must not be so right now. Most notably, impl where-clauses of not yet coinductive traits.
With this, we can change cycles which are definitely unproductive to a proper error. This fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/114. This does not affect stable as we keep these cycles as ambiguous during coherence.
r? ````````@compiler-errors```````` ````````@nikomatsakis````````
Revert <https://github.com/rust-lang/rust/pull/138084> to buy time to
consider options that avoids breaking downstream usages of cargo on
distributed `rustc-src` artifacts, where such cargo invocations fail due
to inability to inherit `lints` from workspace root manifest's
`workspace.lints` (this is only valid for the source rust-lang/rust
workspace, but not really the distributed `rustc-src` artifacts).
This breakage was reported in
<https://github.com/rust-lang/rust/issues/138304>.
This reverts commit 48caf81484, reversing
changes made to c6662879b2.
Use `Binder<Vec<Ty>>` instead of `Vec<Binder<Ty>>` in both solvers for sized/auto traits/etc.
It's more conceptually justified IMO, especially when binders get implications.
r? lcnr
A cycle was previously coinductive if all steps were coinductive.
Change this to instead considerm cycles to be coinductive if they
step through at least one where-bound of an impl of a coinductive
trait goal.
Simplify slice indexing in next trait solver
Unless I'm missing something:
- no need to explicitly specify the end of the slice as the end of the index range
- the `assert` is redundant since the indexing will panic for the same condition
I think this change simplifies it a bit. Also replaced the `for` loop of `push`es with a call to `extend` with an iterator. Might improve performance since it knows how many elements will be added beforehand and can pre-reserve room?
r? `@compiler-errors` , I think
handle global trait bounds defining assoc types
This also fixes the compare-mode for
- tests/ui/coherence/coherent-due-to-fulfill.rs
- tests/ui/codegen/mono-impossible-2.rs
- tests/ui/trivial-bounds/trivial-bounds-inconsistent-projection.rs
- tests/ui/nll/issue-61320-normalize.rs
I first considered the alternative to always prefer where-bounds during normalization, regardless of how the trait goal has been proven by changing `fn merge_candidates` instead. ecda83b30f/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs (L785)
This approach is more restrictive than behavior of the old solver to avoid mismatches between trait and normalization goals. This may be breaking in case the where-bound adds unnecessary region constraints and we currently don't ever try to normalize an associated type. I would like to detect these cases and change the approach to exactly match the old solver if required. I want to minimize cases where attempting to normalize in more places causes code to break.
r? `@compiler-errors`
If a type has unsafe fields, its safety invariants are not simply
the conjunction of its field types' safety invariants. Consequently,
it's invalid to reason about the safety properties of these types
in a purely structural manner — i.e., the manner in which `auto`
traits are implemented.
Makes progress towards #132922.
the behavior of the type system not only depends on the current
assumptions, but also the currentnphase of the compiler. This is
mostly necessary as we need to decide whether and how to reveal
opaque types. We track this via the `TypingMode`.
