Slava Pestov 35daf17dc4 RequirementMachine: Implement RewriteContext::getTypeForTerm() ...

Protocol atoms map to the 'Self' parameter; GenericParam and Name
atoms map in the obvious way.

An associated type atom `[P1&P1&...&Pn:A]` has one or more protocols
P0...Pn and an identifier 'A'.

We map it back to a AssociatedTypeDecl as follows:

- For each protocol Pn, look for associated types A in Pn itself,
  and all protocols that Pn refines.

- For each candidate associated type An in protocol Qn where
  Pn refines Qn, get the associated type anchor An' defined in
  protocol Qn', where Qn refines Qn'.

- Out of all the candidiate pairs (Qn', An'), pick the one where
  the protocol Qn' is the lowest element according to the linear
  order defined by TypeDecl::compare().

The associated type An' is then the canonical associated type
representative of the associated type atom `[P0&...&Pn:A]`.

2021-07-09 00:03:39 -04:00

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