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I forgot to ignore etc.

I want to add a test, but can't figure out how to do it.

@liuxingbaoyu #15160 adds a test for a comment that could never be printed, you could use that and check that we report an error.

This assertion seems overly restrictive, as file.comments is not modified when we transform, which results in reporting comments that the compiler expected or accidentally discarded, and we only want to catch problems with the printer. I will try other methods.

I think this becomes unnecessary after #15144.