Calling CompilerControl.parseTree can return a typechecked tree, which is problematic if what you wanted was just a parsed tree.

It happens because the current implementation tries to memorize the tree. An easy fix is just to re-create the parse tree every time. Tests for this should check that:

1. You get a new parse tree every time you ask for one
2. A parse tree should never contain any symbols or types [1]
3. If you ask for a parse tree and then someone else asks for a typed tree it shouldn't change the parse tree you originally asked for, i.e. property
   2 still holds.

I've discussed this with the IDE team and provided a fix in their project for now but this is something that should be fixed in the compiler. See the ticket here: https://www.assembla.com/spaces/scala-ide/tickets/1001326#/activity/ticket:

I have a fix for this but I need to port my tests from the IDE to the compiler before I can have a pull request ready.

[1] There is an exception to this though. Some of the nodes that
the compiler generates will actually contain symbols. I've
chosen to just ignore these special cases for now.