Show closest candidates for misspellings

[JukkaL]

Instead of just saying "foobar" undefined try to look for closest candidates (using edit distance, for example) and give suggestions. For example: "get_stats" undefined, did you mean "getstats"?.

[JukkaL]

This would be useful for at least these things:

• Attribute lookups
• Keyword argument names
• Module imports

[JukkaL]

There is basic support for attribute lookups in the hack branch.

[JelleZijlstra]

This is done for attribute lookups, but not for the other things Jukka mentions.

[marcodoordash]

#4934 adds more details and use cases to the Module imports part of this issue, pasting those here and closing it as a duplicate of this one.

Mypy can suggest correct spellings for some attributes, but it doesn't seem to work for module attributes:

from subprocess import popen  # Module 'subprocess' has no attribute 'popen'

import subprocess
subprocess.popen  # Module has no attribute "popen"

class Foobar:
    def do_it(self): pass
foobar  # Name 'foobar' is not defined

Foobar().doit()  # "Foobar" has no attribute "doit"; maybe "do_it"?

It would be better if mypy would suggest corrections for all of the cases in the above example.

[marcodoordash]

looking at this one

[Wuisch]

I took a shot at the keyword argument name case. Comments are welcome.

[ilevkivskyi]

This is now fully implemented.