Add Py3k warning for list comprehension target rebinding and regression test

[Eddy114514]

List comprehensions that rebind an outer name (e.g. x in [x = ...; [x for x in ...]] can cause 2.x vs 3.x behavior differences. Specifically, in python 2, it will rebind the outer variable, but in 3.x, it will not.

I added a symbol-table check in symtable.c to detect listcomp target rebinding and emit the warning. I add test in test_grammer.py and it passed on my local machine.

[ltratt]

AFAICS the return int is either 0 or 1 so a bool in disguise? I'm not sure what true/false mean here though: there was/wasn't an error?

[Eddy114514]

I followed the convention of symtable_warn , where the return value indicates whether the check completed successfully or hit an error, not whether a warning was found. So symtable_warn_listcomp_target() and symtable_warn_listcomp_shadowing() return 1 if analysis can continue and 0 only if fail at issuing warning or a recursive check fails.

My comments shows "pending" so it wasn't visible to you as the picture shown below:

@ltratt

[ltratt]

Got it, thanks! [Pending means I didn't see the original comment, alas!].