Internal error when overriding frozen attribute with function #8976

foo.py:10: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.rtfd.io/en/latest/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.790+dev.793cf187f0e529f9d6623a512ae0149124ded542
Traceback (most recent call last):
  File "/home/karl/tools/venv/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/__main__.py", line 8, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/main.py", line 89, in main
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/build.py", line 181, in build
    sources, options, alt_lib_path, flush_errors, fscache, stdout, stderr, extra_plugins
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/build.py", line 252, in _build
    graph = dispatch(sources, manager, stdout)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/build.py", line 2626, in dispatch
    process_graph(graph, manager)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/build.py", line 2949, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/build.py", line 3041, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/semanal_main.py", line 78, in semantic_analysis_for_scc
    process_top_levels(graph, scc, patches)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/semanal_main.py", line 203, in process_top_levels
    patches)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/semanal_main.py", line 331, in semantic_analyze_target
    active_type=active_type)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/semanal.py", line 357, in refresh_partial
    self.refresh_top_level(node)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/semanal.py", line 368, in refresh_top_level
    self.accept(d)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/semanal.py", line 4691, in accept
    node.accept(self)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/nodes.py", line 940, in accept
    return visitor.visit_class_def(self)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/semanal.py", line 1011, in visit_class_def
    self.analyze_class(defn)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/semanal.py", line 1088, in analyze_class
    self.analyze_class_body_common(defn)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/semanal.py", line 1097, in analyze_class_body_common
    self.apply_class_plugin_hooks(defn)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/semanal.py", line 1143, in apply_class_plugin_hooks
    hook(ClassDefContext(defn, decorator, self))
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/plugins/dataclasses.py", line 348, in dataclass_class_maker_callback
    transformer.transform()
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/plugins/dataclasses.py", line 161, in transform
    self._freeze(attributes)
  File "/home/karl/tools/venv/lib/python3.7/site-packages/mypy/plugins/dataclasses.py", line 334, in _freeze
    assert isinstance(var, Var)
AssertionError: 
foo.py:10: : note: use --pdb to drop into pdb