Find a more reliable source origin for diagnostic #30
Description
Coming from m-labs/artiq#1671:
It seems like one of the issue stems from here:
pythonparser/pythonparser/diagnostic.py
Lines 51 to 53 in 5413ee5
And indeed the evaluation of the expression shows there are more than 2 elements.
While the source is clearly different, and it kind of makes sense for the compiler to throw an error like this, shouldn't we find a better source of determining the source origin?
