tree da41bd60a625b438dc2533b6072d6a772e2fbbc1
parent cc7a6e0b2ffed7b6cb3d299e4c37859ad167e06e
author janakr <janakr@google.com> 1558564889 -0700
committer Copybara-Service <copybara-worker@google.com> 1558564969 -0700

Make Artifact an abstract class, and break out a DerivedArtifact subclass. This will facilitate future refactorings in which a DerivedArtifact will have an ActionLookupData "owner", while a SourceArtifact will have a Label owner (or an ArtifactOwner, depending on how lazy I am).

I verified using the test in ArtifactTest, modified to use dummy classes, that derived artifacts don't use any more memory with this refactoring than they did before.

PiperOrigin-RevId: 249535371