Inscrutable error possibly due to failure to infer generic types

[msridhar]

This is related to #3035 and #3044. We may have missed a case there. This is as small as I could make the repro example (reduced from code in https://github.com/h2oai/h2o-3):

class GenericFailure {
    public interface Freezable<T extends Freezable> extends Cloneable {}
    public static final class Key<T extends Keyed> extends Iced<Key<T>> implements Comparable {
        @Override
        public int compareTo(Object o) {
            return 0;
        }
    }
    public abstract static class Keyed<T extends Keyed> extends Iced<T> {}
    public static final class Job<T extends Keyed> extends Keyed<Job> {
        public Job(Key<T> key, String clz_of_T, String desc) {}
    }
    public abstract static class Lockable<T extends Lockable<T>> extends Keyed<T> {}
    public abstract static class Iced<D extends Iced>
            implements Freezable<D>, java.io.Externalizable {
        @Override
        public void readExternal(java.io.ObjectInput ois)
                throws java.io.IOException, ClassNotFoundException {}
        @Override
        public void writeExternal(java.io.ObjectOutput oos) throws java.io.IOException {}
    }
    public abstract static class Model<
                    M extends Model<M, P, O>, P extends Model.Parameters, O extends Model.Output>
            extends Lockable<M> {
        public abstract static class Parameters extends Iced<Parameters> {
            abstract String algoName();
            abstract String javaName();
        }
        public abstract static class Output extends Iced {}
    }
    public abstract static class ModelBuilder<
                    M extends Model<M, P, O>, P extends Model.Parameters, O extends Model.Output>
            extends Iced {
        public static <B extends ModelBuilder, MP extends Model.Parameters> B make(
                MP parms, Key<Model> mKey) {
            Job<Model> mJob = new Job<>(mKey, parms.javaName(), parms.algoName());
            B newMB = ModelBuilder.make(parms.algoName(), mJob, mKey);
            return newMB;
        }
        public static <B extends ModelBuilder> B make(String algo, Job job, Key<Model> result) {
            return null;
        }
    }
}

When I run with tainting checker I get:

$ ./checker/bin/javac -processor TaintingChecker checker/tests/tainting/GenericFailure.java
checker/tests/tainting/GenericFailure.java:54: error: [return.type.incompatible] incompatible types in return.
            return newMB;
                   ^
  type of expression: B extends @Tainted ModelBuilder</*INFERENCE FAILED for:*/ ? extends @Tainted Model</*INFERENCE FAILED for:*/ ?, /*INFERENCE FAILED for:*/ ? extends @Tainted Parameters, /*INFERENCE FAILED for:*/ ? extends @Tainted Output>, /*INFERENCE FAILED for:*/ ? extends @Tainted Parameters, /*INFERENCE FAILED for:*/ ? extends @Tainted Output>
  method return type: B extends @Tainted ModelBuilder</*INFERENCE FAILED for:*/ ? extends @Tainted Model<M extends @Tainted Model<M extends @Tainted Model<M, P extends @Tainted Parameters, O extends @Tainted Output>, P extends @Tainted Parameters, O extends @Tainted Output>, P extends @Tainted Parameters, O extends @Tainted Output>, /*INFERENCE FAILED for:*/ ? extends @Tainted Parameters, /*INFERENCE FAILED for:*/ ? extends @Tainted Output>
1 error

I think we should not be reporting this error unless -AconservativeUninferredTypeArguments is passed.

[msridhar]

I just checked and this passes the checker now! Closing