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
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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