Account for HR lifetimes when suggesting introduction of named lifetime
```
error[E0106]: missing lifetime specifier
--> src/test/ui/suggestions/fn-missing-lifetime-in-item.rs:2:32
|
2 | struct S2<F: Fn(&i32, &i32) -> &i32>(F);
| ---- ---- ^ expected named lifetime parameter
|
= help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from argument 1 or argument 2
= note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
help: consider making the bound lifetime-generic with a new `'a` lifetime
|
2 | struct S2<F: for<'a> Fn(&'a i32, &'a i32) -> &'a i32>(F);
| ^^^^^^^ ^^^^^^^ ^^^^^^^ ^^^
help: consider introducing a named lifetime parameter
|
2 | struct S2<'a, F: Fn(&'a i32, &'a i32) -> &'a i32>(F);=
| ^^^ ^^^^^^^ ^^^^^^^ ^^^
```
Follow up to #68267. Addresses the diagnostics part of #49287.
Address inconsistency in using "is" with "declared here"
"is" was generally used for NLL diagnostics, but not other diagnostics. Using "is" makes the diagnostics sound more natural and readable, so it seems sensible to commit to them throughout.
r? @Centril
This doesn't mention that using an existing lifetime is possible, but
that would hopefully be clear as always being an option. The intention
of this is to teach newcomers what the lifetime syntax is.
Account for common `impl Trait`/`dyn Trait` return type errors
- When all return paths have the same type, suggest `impl Trait`.
- When all return paths implement the expected `trait`, suggest `Box<dyn Trait>` and mention using an `enum`.
- When multiple different types are returned and `impl Trait` is expected, extend the explanation.
- When return type is `impl Trait` and the return paths do not implement `Trait`, point at the returned values.
- Split `src/librustc/traits/error_reporting.rs` into multiple files to keep size under control.
Fix#68110, cc #66523.
When a type error involves a `dyn Trait` as the return type, do not emit
the type error, as the "return type is not `Sized`" error will provide
enough information to the user.
When encountering `_` type placeholder in fn arguments and return type,
suggest using generic type parameters.
Expand what counts as an inferable return type to slice, array and
tuples of `_`.
This still doesn't handle the case entirely correctly, requiring a more
targeted approach with a better suggestion, but at least now the
suggested syntax makes *some* sense.
Initial implementation of `#![feature(bindings_after_at)]`
Following up on #16053, under the gate `#![feature(bindings_after_at)]`, `x @ Some(y)` is allowed subject to restrictions necessary for soundness.
The implementation and test suite should be fairly complete now.
One aspect that is not covered is the interaction with nested `#![feature(or_patterns)]`.
This is not possible to test at the moment in a good way because that feature has not progressed sufficiently and has fatal errors in MIR building. We should make sure to add such tests before we stabilize both features (but shipping one of them is fine).
r? @pnkfelix
cc @nikomatsakis @matthewjasper @pcwalton
cc https://github.com/rust-lang/rust/issues/65490
