If a base class initializer was not generic but had a contextual 'where'
clause, we would unconditionally inherit the 'where' clause in the override as
part of the fix for another issue (https://bugs.swift.org/browse/SR-14118).
However, it is possible that some of those requirements are satisfied by
the derived class itself. For example:
class Base<T> {
init() where T : AnyObject {}
}
class Derived : Base<AnyObject> {}
In this case, the implicit override Derived.init() has no generic requirements
at all. We used to assert because we would create a GSB with no generic
parameters.
It was also possible for a base class initializer to have generic
requirements that are not satisfied by the derived class. In this case,
we need to drop the initializer from consideration altogether.
While I'm here, I improved the comments in computeDesignatedInitOverrideSignature(),
which is the new name for configureGenericDesignatedInitOverride().
Fixes rdar://problem/77285618.
SE-0267 allows where clauses on declarations without their own generic
parameters, which means we can longer assume that if getGenericParams()
returns nullptr on a constructor, then the constructor has the same
generic signature as its parent class.
Instead, explicitly compare the superclass constructor's generic
signature with that of the superclass, and if they don't match,
compute a new generic signature for the override.
Fixes https://bugs.swift.org/browse/SR-14118 / rdar://73764827.
