• Are you reporting a bug, or opening a feature request?

Bug

• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private.

from typing import Dict
from dataclasses import dataclass


@dataclass
class Foo:
    bar: bool


@dataclass
class Bar:
    baz: bool


foo_registry: Dict[str, Foo] = {}
bar_registry: Dict[str, Bar] = {}

use_foo = True

registry = foo_registry if use_foo else bar_registry
registry.get('asdfsdf')

• What is the actual behavior/output?

On the last line, mypy infers that registry has the type object

error: "object" has no attribute "get"

• What is the behavior/output you expect?

mypy infers that the type of registry to be Union[Dict[str, Foo], Dict[str, Bar]] but it looks like this behavior may have been undone by #5095 ?

• What are the versions of mypy and Python you are using?

mypy 0.740 and Python 3.7.2

Do you see the same issue after installing mypy from Git master?

I ran into other issues doing this, but I am on the latest release.

• What are the mypy flags you are using? (For example --strict-optional)

I'm using --strict --warn-unreachable though this occurs with no flags at all.

Thanks for reading.