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bcc9aa01b5
Use fulfillment to check `Drop` impl compatibility Use an `ObligationCtxt` to ensure that a `Drop` impl does not have stricter requirements than the ADT that it's implemented for, rather than using a `SimpleEqRelation` to (more or less) syntactically equate predicates on an ADT with predicates on an impl. r? types ### Some background The old code reads: ```rust // An earlier version of this code attempted to do this checking // via the traits::fulfill machinery. However, it ran into trouble // since the fulfill machinery merely turns outlives-predicates // 'a:'b and T:'b into region inference constraints. It is simpler // just to look for all the predicates directly. ``` I'm not sure what this means, but perhaps in the 8 years since that this comment was written (cc #23638) it's gotten easier to process region constraints after doing fulfillment? I don't know how this logic differs from anything we do in the `compare_impl_item` module. Ironically, later on it says: ```rust // However, it may be more efficient in the future to batch // the analysis together via the fulfill (see comment above regarding // the usage of the fulfill machinery), rather than the // repeated `.iter().any(..)` calls. ``` Also: * Removes `SimpleEqRelation` which was far too syntactical in its relation. * Fixes #110557 |
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For high-level intro to how type checking works in rustc, see the type checking chapter of the rustc dev guide.