How do I add a warning with Groovy AST transformations?

I see on the SourceUnit object that I can addError(SyntaxException)开发者_如何学Go, but how do I add a warning?

EDIT: Anyone know how I can either get a CSTNode in the CompilePhase.SEMANTIC_ANALYSIS, or how I can simply add a warning with only having to know the line number and column number (just like the addError function works)?

EDIT 2: I tried just creating a CSTNode myself, but it didn't seem to work as eclipse didn't show the warning.

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Can you call getErrorCollector() on SourceUnit then add the warnings to that with one of the addWarning(...) methods?