Deduplicate identical region constraints in new solver
the new solver doesn't track whether we've already proven a goal like the fulfillment context's obligation forest does, so we may be instantiating a canonical response (and specifically, its nested region obligations) quite a few times.
This may lead to exponentially gathering up identical region constraints for things like auto traits, so let's deduplicate region constraints when in `compute_external_query_constraints`.
r? ``@lcnr``
Preserve substs in opaques recorded in typeck results
This means that we now prepopulate MIR with opaques with the right substs.
The first commit is a hack that I think we discussed, having to do with `DefiningAnchor::Bubble` basically being equivalent to `DefiningAnchor::Error` in the new solver, so having to use `DefiningAnchor::Bind` instead, lol.
r? `@lcnr`
Deal with unnormalized projections when structurally resolving types with new solver
1. Normalize types in `structurally_resolved_type` when the new solver is enabled
2. Normalize built-in autoderef targets in `Autoderef` when the new solver is enabled
3. Normalize-erasing-regions in `resolve_type` in writeback
This is motivated by the UI test provided, which currently fails with:
```
error[E0609]: no field `x` on type `<usize as SliceIndex<[Foo]>>::Output`
--> <source>:9:11
|
9 | xs[0].x = 1;
| ^
```
I'm pretty happy with the approach in (1.) and (2.) and think we'll inevitably need something like this in the long-term, but (3.) seems like a hack to me. It's a *lot* of work to add tons of new calls to every user of these typeck results though (mir build, late lints, etc). Happy to discuss further.
r? `@lcnr`
do not allow inference in `predicate_must_hold` (alternative approach)
See the FCP description for more info, but tl;dr is that we should not return `EvaluatedToOkModuloRegions` if an obligation may hold only with some choice of inference vars being constrained.
Attempts to solve this in the approach laid out by lcnr here: https://github.com/rust-lang/rust/pull/109558#discussion_r1147318134, rather than by eagerly replacing infer vars with placeholders which is a bit too restrictive.
r? `@ghost`
Note user-facing types of coercion failure
When coercing, for example, `Box<A>` into `Box<dyn B>`, make sure that any failure notes mention *those* specific types, rather than mentioning inner types, like "the cast from `A` to `dyn B`".
I expect end-users are often confused when we skip layers of types and only mention the "innermost" part of a coercion, especially when other notes point at HIR, e.g. #111406.
Uplift `clippy::{drop,forget}_{ref,copy}` lints
This PR aims at uplifting the `clippy::drop_ref`, `clippy::drop_copy`, `clippy::forget_ref` and `clippy::forget_copy` lints.
Those lints are/were declared in the correctness category of clippy because they lint on useless and most probably is not what the developer wanted.
## `drop_ref` and `forget_ref`
The `drop_ref` and `forget_ref` lint checks for calls to `std::mem::drop` or `std::mem::forget` with a reference instead of an owned value.
### Example
```rust
let mut lock_guard = mutex.lock();
std::mem::drop(&lock_guard) // Should have been drop(lock_guard), mutex
// still locked
operation_that_requires_mutex_to_be_unlocked();
```
### Explanation
Calling `drop` or `forget` on a reference will only drop the reference itself, which is a no-op. It will not call the `drop` or `forget` method on the underlying referenced value, which is likely what was intended.
## `drop_copy` and `forget_copy`
The `drop_copy` and `forget_copy` lint checks for calls to `std::mem::forget` or `std::mem::drop` with a value that derives the Copy trait.
### Example
```rust
let x: i32 = 42; // i32 implements Copy
std::mem::forget(x) // A copy of x is passed to the function, leaving the
// original unaffected
```
### Explanation
Calling `std::mem::forget` [does nothing for types that implement Copy](https://doc.rust-lang.org/std/mem/fn.drop.html) since the value will be copied and moved into the function on invocation.
-----
Followed the instructions for uplift a clippy describe here: https://github.com/rust-lang/rust/pull/99696#pullrequestreview-1134072751
cc `@m-ou-se` (as T-libs-api leader because the uplifting was discussed in a recent meeting)
Don't compute trait super bounds unless they're positive
Fixes#111207
The comment is modified to explain the rationale for why we even have this recursive call to supertraits in the first place, which doesn't apply to negative bounds since they don't elaborate at all.
Tweak await span to not contain dot
Fixes a discrepancy between method calls and await expressions where the latter are desugared to have a span that *contains* the dot (i.e. `.await`) but method call identifiers don't contain the dot. This leads to weird suggestions suggestions in borrowck -- see linked issue.
Fixes#110761
This mostly touches a bunch of tests to tighten their `await` span.
Use `?0` notation for ty/ct/int/float/region vars
Aligns the notation for infer vars that T-types and friends most often uses for inference variables with the notation in the compiler (which is kinda a sigil nightmare IMO: `_#`) by adopting `?0` style infer vars.
This mostly affects debug output since verbose infer vars shouldn't show up in user-facing places.
Does this need an MCP? It's debug output, so I'm thinking no, but happy to open one. 🤔
r? types
Clone region var origins instead of taking them in borrowck
Fixes an issue with the new solver where reporting a borrow-checker error ICEs because it calls `InferCtxt::evaluate_obligation`.
This also removes a handful of unnecessary `tcx.infer_ctxt().build()` calls that are only there to mitigate this same exact issue, but with the old solver.
Fixescompiler-errors/next-solver-hir-issues#12.
----
This implements `@aliemjay's` solution where we just don't *take* the region constraints, but clone them. This potentially makes it easier to write a bug about taking region constraints twice or never at all, but again, not many folks are touching this code.
don't uniquify regions when canonicalizing
uniquifying causes a bunch of issues, most notably it causes `AliasEq(<?x as Trait<'a>>::Assoc, <?x as Trait<'a>>::Assoc)` to result in ambiguity because both `normalizes-to` paths result in ambiguity and substs equate should trivially succeed but doesn't because we uniquified `'a` to two different regions.
I originally added uniquification to make it easier to deal with requirement 6 from the dev-guide: https://rustc-dev-guide.rust-lang.org/solve/trait-solving.html#requirements
> ### 6. Trait solving must be (free) lifetime agnostic
>
> Trait solving during codegen should have the same result as during typeck. As we erase
> all free regions during codegen we must not rely on them during typeck. A noteworthy example
> is special behavior for `'static`.
cc https://github.com/rust-lang/rustc-dev-guide/pull/1671
Relying on regions being identical may cause ICE during MIR typeck, but even without this PR we can end up relying on that as type inference vars can resolve to types which contain an identical region. Let's land this and deal with any ICE that crop up as we go. Will look at this issue again before stabilization.
r? ```@compiler-errors```
