Improve generic mapped type relations #13448
Merged
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This PR improves type relationships for generic mapped types: A mapped type
{ [P in S]: X }
is related to a mapped type{ [Q in T]: Y }
ifT
is related toS
andX'
is related toY
, whereX'
is an instantiation ofX
in whichP
is replaced withQ
. Notice thatS
andT
are contra-variant whereasX
andY
are co-variant.Fixes #12832.