ISTM that it is kind of a regression, because logically this is about the scan state so it should be in the corresponding structure, and having two structures to pass the scan state is not an improvement...
I wasn't too happy with the extra param, either. Having moved the guts to conditional.c, I'm happy with that change and can move the stack head back to scan_state with a clear conscience.
I would suggest to also apply the advice to the example shown, including a comment about why the variable is set on.
+1
Also, the last element of the tap tests should be distinct: I suggest to use 'if syntax error' and 'elif syntax error' in place of 'syntax error' for the two first tests.
