rust/compiler/rustc_traits
Aaron Hill 93ab12eeab
Improve cause information for NLL higher-ranked errors
This PR has several interconnected pieces:

1. In some of the NLL region error code, we now pass
   around an `ObligationCause`, instead of just a plain `Span`.
   This gets forwarded into `fulfill_cx.register_predicate_obligation`
   during error reporting.
2. The general InferCtxt error reporting code is extended to
   handle `ObligationCauseCode::BindingObligation`
3. A new enum variant `ConstraintCategory::Predicate` is added.
   We try to avoid using this as the 'best blame constraint' - instead,
   we use it to enhance the `ObligationCause` of the `BlameConstraint`
   that we do end up choosing.

As a result, several NLL error messages now contain the same
"the lifetime requirement is introduced here" message as non-NLL
errors.

Having an `ObligationCause` available will likely prove useful
for future improvements to NLL error messages.
2021-09-27 10:23:45 -05:00
..
src Improve cause information for NLL higher-ranked errors 2021-09-27 10:23:45 -05:00
Cargo.toml Migrate to 2021 2021-09-20 22:21:42 -04:00