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.
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.
When a trait bound is not met and restricting a type parameter would
make the restriction hold, use a structured suggestion pointing at an
appropriate place (type param in param list or `where` clause).
Account for opaque parameters where instead of suggesting extending
the `where` clause, we suggest appending the new restriction:
`fn foo(impl Trait + UnmetTrait)`.
This gives at least some explanation for why a borrow is expected to
last for a certain free region. Also:
* Reports E0373: "closure may outlive the current function" with NLL.
* Special cases the case of returning a reference to (or value
referencing) a local variable or temporary (E0515).
* Special case assigning a reference to a local variable in a closure
to a captured variable.
This commit updates the test output for the updated NLL compare mode
that uses `-Z borrowck=migrate` rather than `-Z borrowck=mir`. The
previous commit changes `compiletest` and this commit only updates
`.nll.stderr` files.
