Remove identity casts from optimizer

[zachyee]

prestodb#4259

@maciejgrzybek

[maciejgrzybek]

from optimizer is not necessary in commit msg.
What about Add remove identity casts rewriter?
Commit msgs guidelines: http://chris.beams.io/posts/git-commit/

[maciejgrzybek]

requireNonNull

[maciejgrzybek]

Back to you, @zachyee.

[zachyee]

I addressed the easy-to-fix comments. I responded with some info on the harder-to-fix comments to figure out what would be best before trying to address them. @maciejgrzybek

[kokosing]

I don't like this name. As it is a plan. Maybe assertPlanDoesNotMatch

[kokosing]

It is a expression tree and you check only the root of it.

[kokosing]

I think you should use ExpressionVerifier here and compare expected expression vs actual one.

[kokosing]

IMO interface here is an over engineering. I would prefer abstract class with below methods implemented.

[maciejgrzybek]

Why this iface is needed at all?