Module rustc_trait_selection::solve::alias_relate

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Implements the AliasRelate goal, which is used when unifying aliases. Doing this via a separate goal is called “deferred alias relation” and part of our more general approach to “lazy normalization”.

This goal, e.g. A alias-relate B, may be satisfied by one of three branches:

  • normalizes-to: If A is a projection, we can prove the equivalent projection predicate with B as the right-hand side of the projection. This goal is computed in both directions, if both are aliases.
  • subst-relate: Equate A and B by their substs, if they’re both aliases with the same def-id.
  • bidirectional-normalizes-to: If A and B are both projections, and both may apply, then we can compute the “intersection” of both normalizes-to by performing them together. This is used specifically to resolve ambiguities.

Enums

  • Invert 🔒
    We may need to invert the alias relation direction if dealing an alias on the RHS.