Slava Pestov ae56af36d2 RequirementMachine: Workaround invariant violation when requirement signature completion fails ...

- If P is declared to inherit from Q and Q has an associated type named U, then
  isValidTypeInContext() returns true for a type 'T.U' where 'T' is a generic
  parameter conforming to P, and 'U' is the unresolved DependentMemberType, and
  the type 'T.U' will simplify to the term 'T.[P:U]'.

- However, if completion failed while building the rewrite system for P's
  requirement signature, then the requirement signature for P won't have a
  rule [P].[Q] => [P]. As a result, getTypeForTerm() will fail when given
  'T.[P:U]', because the property map entry for 'T' will not contain a
  conformance to Q.

Work around this by manually adding protocol inheritance rules when building
a signature from a protocol whose requirement signature failed to compute.

This was triggered by the test case I added in the previous commit to
test/Generics/non_confluent.swift.

2022-05-09 21:21:35 -04:00

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