anchor.diff:      } else if (prefixExpectations != null) {
         for (_PrefixExpectation expectation in prefixExpectations) {
           expect(reference.prefixReference, isNot(0));
  -        reference = checkReferenceIndex(
  -            reference.prefixReference,
  -            expectation.inLibraryDefiningUnit
  -                ? null
  -                : expectation.absoluteUri ?? absoluteUri,
  -            expectation.inLibraryDefiningUnit
  -                ? null
  -                : expectation.relativeUri ?? relativeUri,
  -            expectation.name,
  +        reference = checkReferenceIndex(reference.prefixReference,
  +            expectation.absoluteUri, expectation.relativeUri, expectation.name,
               expectedKind: expectation.kind,
               checkAstDerivedDataOverride: checkAstDerivedDataOverride,
               expectedTargetUnit: expectedTargetUnit,
  
positive.code:       (EntityRef r) => checkTypeRef(r, absUri('/a.dart'), 'a.dart', 'f',
                expectedKind: ReferenceKind.topLevelFunction,
                prefixExpectations: [
                  new _PrefixExpectation(ReferenceKind.prefix, 'p',
                      inLibraryDefiningUnit: true)
                ])
      ]);
    }
  
negative.code:               prefixExpectations: [
                  new _PrefixExpectation(ReferenceKind.classOrEnum, 'C',
                      absoluteUri: absUri('/a.dart'), relativeUri: 'a.dart'),
                  new _PrefixExpectation(ReferenceKind.prefix, 'p')
                ])
      ]);
    }
  