Nothing else makes sense, and there is no "danger" in doing so, as it only does something if there are const bounds, which are unstable. This used to happen implicitly via the inferctxt before, which was much more fragile.
Print associated types on opaque `impl Trait` types
This PR generalizes #91021, printing associated types for all opaque `impl Trait` types instead of just special-casing for future.
before:
```
error[E0271]: type mismatch resolving `<impl Iterator as Iterator>::Item == u32`
```
after:
```
error[E0271]: type mismatch resolving `<impl Iterator<Item = usize> as Iterator>::Item == u32`
```
---
Questions:
1. I'm kinda lost in binders hell with this one. Is all of the `rebind`ing necessary?
2. Is there a map collection type that will give me a stable iteration order? Doesn't seem like TraitRef is Ord, so I can't just sort later..
3. I removed the logic that suppresses printing generator projection types. It creates outputs like this [gist](https://gist.github.com/compiler-errors/d6f12fb30079feb1ad1d5f1ab39a3a8d). Should I put that back?
4. I also added spaces between traits, `impl A+B` -> `impl A + B`. I quite like this change, but is there a good reason to keep it like that?
r? ````@estebank````
Elaborate `Future::Output` when printing opaque `impl Future` type
I would love to see the `Output =` type when printing type errors involving opaque `impl Future`.
[Test code](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=a800b481edd31575fbcaf5771a9c3678)
Before (cut relevant part of output):
```
note: while checking the return type of the `async fn`
--> /home/michael/test.rs:5:19
|
5 | async fn bar() -> usize {
| ^^^^^ checked the `Output` of this `async fn`, found opaque type
= note: expected type `usize`
found opaque type `impl Future`
```
After:
```
note: while checking the return type of the `async fn`
--> /home/michael/test.rs:5:19
|
5 | async fn bar() -> usize {
| ^^^^^ checked the `Output` of this `async fn`, found opaque type
= note: expected type `usize`
found opaque type `impl Future<Output = usize>`
```
Note the "found opaque type `impl Future<Output = usize>`" in the new output.
----
Questions:
1. We skip printing the output type when it's a projection, since I have been seeing some types like `impl Future<Output = <[static generator@/home/michael/test.rs:2:11: 2:21] as Generator<ResumeTy>>::Return>` which are not particularly helpful and leak implementation detail.
* Am I able to normalize this type within `rustc_middle::ty::print::pretty`? Alternatively, can we normalize it when creating the diagnostic? Otherwise, I'm fine with skipping it and falling back to the old output.
* Should I suppress any other types? I didn't encounter anything other than this generator projection type.
2. Not sure what the formatting of this should be. Do I include spaces in `Output = `?
fix CTFE/Miri simd_insert/extract on array-style repr(simd) types
The changed test would previously fail since `place_index` would just return the only field of `f32x4`, i.e., the array -- rather than *indexing into* the array which is what we have to do.
The new helper methods will also be needed for https://github.com/rust-lang/miri/issues/1912.
r? ``````@oli-obk``````
This function parameter attribute was introduced in https://github.com/rust-lang/rust/pull/44866 as an intermediate step in implementing `impl Trait`, it's not necessary or used anywhere by itself.
Because it's always `'tcx`. In fact, some of them use a mixture of
passed-in `$tcx` and hard-coded `'tcx`, so no other lifetime would even
work.
This makes the code easier to read.
implement rfc-2528 type_changing-struct-update
This PR implement rfc2528-type_changing-struct-update.
The main change process is as follows:
1. Move the processing part of `base_expr` into `check_expr_struct_fields` to avoid returning `remaining_fields` (a relatively complex hash table)
2. Before performing the type consistency check(`check_expr_has_type_or_error`), if the `type_changing_struct_update` feature is set, enter a different processing flow, otherwise keep the original flow
3. In the case of the same structure definition, check each field in `remaining_fields`. If the field in `base_expr` is not the suptype of the field in `adt_ty`, an error(`FeildMisMatch`) will be reported.
The MIR part does not need to be changed, because only the items contained in `remaining_fields` will be extracted from `base_expr` when MIR is generated. This means that fields with different types in `base_expr` will not be used
Updates #86618
cc `@nikomatsakis`
Implement coherence checks for negative trait impls
The main purpose of this PR is to be able to [move Error trait to core](https://github.com/rust-lang/project-error-handling/issues/3).
This feature is necessary to handle the following from impl on box.
```rust
impl From<&str> for Box<dyn Error> { ... }
```
Without having negative traits affect coherence moving the error trait into `core` and moving that `From` impl to `alloc` will cause the from impl to no longer compiler because of a potential future incompatibility. The compiler indicates that `&str` _could_ introduce an `Error` impl in the future, and thus prevents the `From` impl in `alloc` that would cause overlap with `From<E: Error> for Box<dyn Error>`. Adding `impl !Error for &str {}` with the negative trait coherence feature will disable this error by encoding a stability guarantee that `&str` will never implement `Error`, making the `From` impl compile.
We would have this in `alloc`:
```rust
impl From<&str> for Box<dyn Error> {} // A
impl<E> From<E> for Box<dyn Error> where E: Error {} // B
```
and this in `core`:
```rust
trait Error {}
impl !Error for &str {}
```
r? `@nikomatsakis`
This PR was built on top of `@yaahc` PR #85764.
Language team proposal: to https://github.com/rust-lang/lang-team/issues/96
