Exclude undefined
from constraints of mapped type type parameters
#59995
+292
−2
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fixes #59987
see @ahejlsberg's comment here about homomorphic mapped types and their constraints
given that
keyof X
(and the same is true about[K in ...]
) should never includeundefined
, I think it should be fairly OK to eliminateundefined
from such rogue instantiations that might happen