Performance error when clicking in some tokens

[dpordomingo]

as reported by @vmarkovtsev vía Slack:

I found a bug. Open fizzbuzz.py and click on "return" in "return 'Buzz'". It freezes and kills the tab

Diagnostic:

There is a performance error when clicking in some tokens, that causes a browser tab freeze.

given the following python sourcecode:

def fizzbuzz(n):
    if false:
        return 'Fizz'
    else:
        return 'FizzBuzz'

click in the last return -> small freeze
click in FizzBuzz -> looooong freeze

[dpordomingo]

I spotted the merge causing the problem:
https://github.com/bblfsh/dashboard/pull/19/files
It was added to (recursively) uncollapse a highlited node.

[dpordomingo]

It does not depend on the language;
It depends on the complexity of the source code -> deepness of the UAST.
It's more likely to occur when the clicked token is really deep in the UAST.