Slava Pestov 762bf1e7d0 RequirementMachine: Refine 'derived via protocol typealias' criterion ...

Preserves concrete type rules on associated types that were derived
from rules indirectly formed from protocol typealias rules.

That is, if you have a pair of rules in another minimization domain:

    [P].A.[concrete: C] => [P].A
    [Q:T].[P] => [Q:T]

Then completion will introduce a new rule:

    [Q:T].A.[concrete: C] => [Q:T].A

Since this rule is outside of our minimization domain, we don't record
a rewrite loop for it, and it will never become redundant.

Now if we have a rule in our own minimization domain:

    T.[Q:T].A => T.[Q:U]

Then we get a new rule:

    T.[Q:U].[concrete: C] => T.[Q:U]

Make sure we keep this rule around on account of it being derived from
([Q:T].A.[concrete: C] => [Q:T].A).

2022-03-14 12:33:18 -04:00

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