The stable ABI, because flix.jar does not have one.

Flix's internals carry no compatibility promise: Bootstrap, TypedAst and everything under them may be reorganised in any release, and have been. A plugin that spreads knowledge of those types through its own code inherits that instability everywhere, and every new compiler becomes an edit in a dozen places.

So the instability is confined instead. This interface is the only thing the rest of the plugin knows about a compiler, and it is Java, and versionless on purpose: everything crossing it is a string, a number or a boolean. One implementation per Flix generation sits behind it, written against that generation's AST, and nothing outside those implementations imports ca.uwaterloo.flix.

Per declaration, not aggregate. An earlier version returned totals, which was enough to print a summary and useless for anything else: a finding has to name a file and a line, a ranking has to compare definitions to each other, and "the worst three" cannot be recovered from a sum. Returning records costs nothing in coupling — none of them mention a compiler type — and is what lets every smell, format and ranking live outside the adapter.

Implementing one

Implementations must be instantiable with a public no-argument constructor and named in Adapters. They are loaded reflectively by name, which is what keeps them off the class path of the phase that has no compiler: an adapter is only ever loaded in a JVM that already has the compiler it was written for.