Only convert Guava Predicate when not used as method argument

[timtebeek]

@lredor I'm considering this change to avoid the compilation issues you saw, without potentially changing performance or semantics. This fits into our "do no harm", to avoid making potentially breaking changes whist still migrating what we can.

Any thoughts before a merge?

• Fixes Iterables.filter(Iterable<T> unfiltered, com.google.common.base.Predicat) is not correctly handed by PreferJavaUtilPredicate recipe #883

• Fixes Sets.filter is not migrated, which creates a conflict with the PreferJavaUtilPredicate recipe #897

• Fixes Collections2.filter is not migrated, which creates a conflict with the PreferJavaUtilPredicate recipe #899

• Closes Convert Guava Collections2.filter #900

[lredor]

Any thoughts before a merge?

I've amended your PR with the changes from PR #904.

It’s a pity to also exclude methods like Predicates.not() (which can be safely converted). Is there a way to be more selective?
What I have in mind is to get the list of methods using the "predicate" and check whether all of these "users" belong to a known list of methods already handled by other recipes (instead of using the global Preconditions.not(new UsesMethod<>("*..* *(.., com.google.common.base.Predicate)")).

But overall, I’m fine with the PR to respect the "do no harm" principle.

[timtebeek]

Thanks! Pushed up a small change just now to at least allow not to be converted still; we can indeed be more selective but figured this would be the safest way to go about it; as long as we migrate the predicate type last any others covered with dedicated recipes should at least be converted without accommodations here. Thanks for the helpful nudges!

[lredor]

There is at least one problem with this PR: the conversion of the apply method into test method of the Predicate type does not follow the same rule as its type. I described it in issue #908 (which is more of a general issue about Predicate).