fix #36869, incorrect intersection with Union in supertype
#36996
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JeffBezanson
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types and dispatch
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I don't have a great solution to this, but fortunately in this case one of the types is concrete so a shortcut is possible.
The basic problem is the constraint
Union{T, S} == Union{A, B}, where T and S are variables and A and B are types. We know the subtype relation holds, so that part is fine, but the values of T and S are not uniquely defined. In this case we were takingT == Union{A, B}andS == A. That makes it very difficult to use parameter values inferred from a supertype in intersection. As a next step we could perhaps try some heuristic for when it is "safe" to use the inferred values, e.g. if the variables appear as direct parameters of the supertype.fixes #36869