Fix #11312: nonlocal does not raise SyntaxError

[felixzhuologist]

As we traverse the AST, keep track of the depth in terms of the function call stack so that we can check for different invalid AstNodes at each depth and terminate early when possible. Fixes #11312

[felixzhuologist]

@Carreau I'd like to add a test for this but I couldn't figure out how to run tests - I tried various forms of python3 -m unittest core.tests.test_async_helpers but ended up getting import errors. Would you be able to point me to some info about running unittests?

[Carreau]

running test is a bit weird as we are a python shell.
You need to not be in IPython directory and run iptest

To run a single test I would for example run

$ cd ; iptest IPython.core.tests.test_inputtransformer2:test_check_complete; cd -

You can also just push on the branch and let Travis CI work for you :-)

[felixzhuologist]

Awesome, that works. Thanks!

[minrk]

Thanks!