Improve unresolved use error message
"use of undeclared type or module `foo`" doesn't mention that it could be a crate.
This error can happen when users forget to add a dependency to `Cargo.toml`, so I think it's important to mention that it could be a missing crate.
I've used a heuristic based on Rust's naming conventions. It complains about an unknown type if the ident starts with an upper-case letter, and crate or module otherwise. It seems to work very well. The expanded error help covers both an unknown type and a missing crate case.
If a symbol name can only be imported from one place for a type, and
as long as it was not glob-imported anywhere in the current crate, we
can trim its printed path and print only the name.
This has wide implications on error messages with types, for example,
shortening `std::vec::Vec` to just `Vec`, as long as there is no other
`Vec` importable anywhere.
This adds a new '-Z trim-diagnostic-paths=false' option to control this
feature.
On the good path, with no diagnosis printed, we should try to avoid
issuing this query, so we need to prevent trimmed_def_paths query on
several cases.
This change also relies on a previous commit that differentiates
between `Debug` and `Display` on various rustc types, where the latter
is trimmed and presented to the user and the former is not.
Account for multiple impl/dyn Trait in return type when suggesting `'_`
Make `impl` and `dyn` Trait lifetime suggestions a bit more resilient.
Follow up to #72804.
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.
Only display other method receiver candidates if they actually apply
Previously, we would suggest `Box<Self>` as a valid receiver, even if
method resolution only succeeded due to an autoderef (e.g. to `&self`)
Further tweak lifetime errors involving `dyn Trait` and `impl Trait` in return position
* Suggest substituting `'static` lifetime in impl/dyn `Trait + 'static` instead of `Trait + 'static + '_`
* When `'static` is explicit, also suggest constraining argument with it
* Reduce verbosity of suggestion message and mention lifetime in label
* Tweak output for overlapping required/captured spans
* Give these errors an error code
Follow up to #72543.
r? @nikomatsakis
Don't create impl candidates when obligation contains errors
Fixes#72839
In PR #72621, trait selection was modified to no longer bail out early
when an error type was encountered. This allowed us treat `ty::Error` as
`Sized`, causing us to avoid emitting a spurious "not sized" error after
a type error had already occured.
However, this means that we may now try to match an impl candidate
against the error type. Since the error type will unify with almost
anything, this can cause us to infinitely recurse (eventually triggering
an overflow) when trying to verify certain `where` clauses.
This commit causes us to skip generating any impl candidates when an
error type is involved.
