Code pattern matching should ignore difference between overriding and overridden symbols about squid HOT 1 CLOSED

Implementation-wise, one tricky thing is that a Scala method may implement/override several distinct methods defined in different traits, so we can't just go up the override chain and always pick a single ancestor symbol to use as a representative. Conceptually, we'd need to maintain sets of base method symbols, and test for set intersection during pattern matching. But that seems pretty inefficient.

An alternative would be to use a union-find data structure, where two symbols are unified if one overrides the other. This basically means that, perhaps counter-intuitively, two method symbols may be always considered equivalent if there exists a type containing a method that overrides both of them. The existence of such a type tells us that their signatures are compatible, and Scala's type checking of both the pattern and the source programs should ensure that we never end up making an unsound match.

We have to change the definition of the MtdSymbol member type in most existing Squid Base implementations from scala.reflect.runtime.universe.MethodSymbol to that union-find data structure, which seems like a little bit of a hassle but should be doable.

from squid.