Verify that the binop trait *is* implemented for the types *if* all the
involved type parameters are replaced with fresh inferred types. When
this is the case, it means that the type parameter was indeed missing a
trait bound. If this is not the case, provide a generic `note` refering
to the type that doesn't implement the expected trait.
Try to suggest dereferences on trait selection failed
Fixes#39029Fixes#62530
This PR consists of two parts:
1. Decouple `Autoderef` with `FnCtxt` and move `Autoderef` to `librustc_trait_selection`.
2. Try to suggest dereferences when trait selection failed.
The first is needed because:
1. For suggesting dereferences, the struct `Autoderef` should be used. But before this PR, it is placed in `librustc_typeck`, which depends on `librustc_trait_selection`. But trait selection error emitting happens in `librustc_trait_selection`, if we want to use `Autoderef` in it, dependency loop is inevitable. So I moved the `Autoderef` to `librustc_trait_selection`.
2. Before this PR, `FnCtxt` is coupled to `Autoderef`, and `FnCtxt` only exists in `librustc_typeck`. So decoupling is needed.
After this PR, we can get suggestion like this:
```
error[E0277]: the trait bound `&Baz: Happy` is not satisfied
--> $DIR/trait-suggest-deferences-multiple.rs:34:9
|
LL | fn foo<T>(_: T) where T: Happy {}
| ----- required by this bound in `foo`
...
LL | foo(&baz);
| ^^^^
| |
| the trait `Happy` is not implemented for `&Baz`
| help: consider adding dereference here: `&***baz`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0277`.
```
r? @estebank
Unify region variables when projecting associated types
This is required to avoid cycles when evaluating auto trait predicates.
Notably, this is required to be able add Chalk types to `CtxtInterners` for `cfg(parallel_compiler)`.
r? @nikomatsakis
Specialization is unsound
As discussed in https://github.com/rust-lang/rust/issues/31844#issuecomment-617013949, it might be a good idea to warn users of specialization that the feature they are using is unsound.
I also expanded the "incomplete feature" warning to link the user to the tracking issue.
Fix trait alias inherent impl resolution
Fixes#60021 and fixes#72415.
Obviously, the fix was very easy, but getting started with the testing and debugging rust compiler was an interesting experience. Now I can cross it off my bucket list!
Detect type parameter that might require lifetime constraint.
Do not name `ReVar`s in expected/found output.
Reword text suggesting to check the lifetimes.
Fix suggestion to borrow in struct
The corresponding issue is #71136.
The compiler suggests that borrowing `the_foos` might solve the problem. This is obviously incorrect.
```
struct Foo(u8);
#[derive(Clone)]
struct FooHolster {
the_foos: Vec<Foo>,
}
```
I propose as fix to check if there is any colon in the span. However, there might a case where `my_method(B { a: 1, b : foo })` would be appropriate to show a suggestion for `&B ...`. To fix that too, we can simply check if there is a bracket in the span. This is only possible because both spans are different.
Issue's span: `the_foos: Vec<Foo>`
other's span: `B { a : 1, b : foo }`
When evaluating the derived obligations from super traits, maintain a
reference to the original obligation in order to give more actionable
context in the output.
They used to be covered by `optin_builtin_traits` but negative impls
are now applicable to all traits, not just auto traits.
This also adds docs in the unstable book for the current state of auto traits.
Increase verbosity when suggesting subtle code changes
Do not suggest changes that are actually quite small inline, to minimize the likelihood of confusion.
Fix#69243.
