Crash when using `TypeAlias` inside a dataclass

[AlexWaygood]

Crash Report

The following snippet of code causes a crash:

from dataclasses import dataclass
from typing import TypeAlias

class Foo:
    x = 1

@dataclass
class A:
    ShortName: TypeAlias = Foo
    var: int = ShortName.x

It doesn't work as expected at runtime, but it also probably shouldn't cause mypy to crash.

Traceback

test.py:8: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.950+dev.222029b07e0fdcb3c174f15b61915b3b2e1665ca
Traceback (most recent call last):
  File "C:\Users\alexw\coding\mypy\venv\Scripts\mypy-script.py", line 33, in <module>
    sys.exit(load_entry_point('mypy', 'console_scripts', 'mypy')())
  File "c:\users\alexw\coding\mypy\mypy\__main__.py", line 12, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "c:\users\alexw\coding\mypy\mypy\main.py", line 96, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "c:\users\alexw\coding\mypy\mypy\main.py", line 173, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "c:\users\alexw\coding\mypy\mypy\build.py", line 180, in build
    result = _build(
  File "c:\users\alexw\coding\mypy\mypy\build.py", line 256, in _build
    graph = dispatch(sources, manager, stdout)
  File "c:\users\alexw\coding\mypy\mypy\build.py", line 2733, in dispatch
    process_graph(graph, manager)
  File "c:\users\alexw\coding\mypy\mypy\build.py", line 3081, in process_graph
    process_stale_scc(graph, scc, manager)
  File "c:\users\alexw\coding\mypy\mypy\build.py", line 3173, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "c:\users\alexw\coding\mypy\mypy\semanal_main.py", line 78, in semantic_analysis_for_scc
    process_top_levels(graph, scc, patches)
  File "c:\users\alexw\coding\mypy\mypy\semanal_main.py", line 199, in process_top_levels
    deferred, incomplete, progress = semantic_analyze_target(next_id, state,
  File "c:\users\alexw\coding\mypy\mypy\semanal_main.py", line 326, in semantic_analyze_target
    analyzer.refresh_partial(refresh_node,
  File "c:\users\alexw\coding\mypy\mypy\semanal.py", line 414, in refresh_partial
    self.refresh_top_level(node)
  File "c:\users\alexw\coding\mypy\mypy\semanal.py", line 425, in refresh_top_level
    self.accept(d)
  File "c:\users\alexw\coding\mypy\mypy\semanal.py", line 5281, in accept
    node.accept(self)
  File "c:\users\alexw\coding\mypy\mypy\nodes.py", line 1021, in accept
    return visitor.visit_class_def(self)
  File "c:\users\alexw\coding\mypy\mypy\semanal.py", line 1120, in visit_class_def
    self.analyze_class(defn)
  File "c:\users\alexw\coding\mypy\mypy\semanal.py", line 1200, in analyze_class
    self.analyze_class_body_common(defn)
  File "c:\users\alexw\coding\mypy\mypy\semanal.py", line 1209, in analyze_class_body_common
    self.apply_class_plugin_hooks(defn)
  File "c:\users\alexw\coding\mypy\mypy\semanal.py", line 1255, in apply_class_plugin_hooks
    hook(ClassDefContext(defn, decorator, self))
  File "c:\users\alexw\coding\mypy\mypy\plugins\dataclasses.py", line 521, in dataclass_class_maker_callback
    transformer.transform()
  File "c:\users\alexw\coding\mypy\mypy\plugins\dataclasses.py", line 121, in transform
    attributes = self.collect_attributes()
  File "c:\users\alexw\coding\mypy\mypy\plugins\dataclasses.py", line 327, in collect_attributes
    assert isinstance(node, Var)
AssertionError:

To Reproduce

Paste the code above into a .py file, run mypy on it. Also reproduced on mypy playground.