[2.0 regression] Crash with --allow-redefinition on partial type with global #21423

λ cat test250.py
x = []

def f() -> None:
    global x
    x

λ mypy --no-incremental --show-traceback --allow-redefinition test250.py
test250.py:5: 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: 2.1.0+dev.16823a17c10ce5a00b0bbdee5fa9959dccea8ccc
Traceback (most recent call last):
  File "/Users/shantanu/.virtualenvs/mypy-fexc/bin/mypy", line 10, in <module>
    sys.exit(console_entry())
  File "/Users/shantanu/dev/mypy/mypy/__main__.py", line 16, in console_entry
    main()
  File "/Users/shantanu/dev/mypy/mypy/main.py", line 154, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "/Users/shantanu/dev/mypy/mypy/main.py", line 244, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/Users/shantanu/dev/mypy/mypy/build.py", line 422, in build
    result = build_inner(
  File "/Users/shantanu/dev/mypy/mypy/build.py", line 537, in build_inner
    graph = dispatch(sources, manager, stdout, connect_threads)
  File "/Users/shantanu/dev/mypy/mypy/build.py", line 4150, in dispatch
    process_graph(graph, manager)
  File "/Users/shantanu/dev/mypy/mypy/build.py", line 4618, in process_graph
    done, still_working, results = manager.wait_for_done(graph)
  File "/Users/shantanu/dev/mypy/mypy/build.py", line 1492, in wait_for_done
    process_stale_scc(graph, next_scc, self)
  File "/Users/shantanu/dev/mypy/mypy/build.py", line 4792, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/Users/shantanu/dev/mypy/mypy/build.py", line 3414, in type_check_first_pass
    self.type_checker().check_first_pass(recurse_into_functions=recurse_into_functions)
  File "/Users/shantanu/dev/mypy/mypy/checker.py", line 618, in check_first_pass
    self.accept(d)
  File "/Users/shantanu/dev/mypy/mypy/checker.py", line 765, in accept
    stmt.accept(self)
  File "/Users/shantanu/dev/mypy/mypy/nodes.py", line 1159, in accept
    return visitor.visit_func_def(self)
  File "/Users/shantanu/dev/mypy/mypy/checker.py", line 1332, in visit_func_def
    self.visit_func_def_impl(defn)
  File "/Users/shantanu/dev/mypy/mypy/checker.py", line 1336, in visit_func_def_impl
    self.check_func_item(defn, name=defn.name)
  File "/Users/shantanu/dev/mypy/mypy/checker.py", line 1369, in check_func_item
    self.check_func_def(defn, typ, name, allow_empty)
  File "/Users/shantanu/dev/mypy/mypy/checker.py", line 1551, in check_func_def
    self.accept(item.body)
  File "/Users/shantanu/dev/mypy/mypy/checker.py", line 765, in accept
    stmt.accept(self)
  File "/Users/shantanu/dev/mypy/mypy/nodes.py", line 1816, in accept
    return visitor.visit_block(self)
  File "/Users/shantanu/dev/mypy/mypy/checker.py", line 3275, in visit_block
    self.accept(s)
  File "/Users/shantanu/dev/mypy/mypy/checker.py", line 765, in accept
    stmt.accept(self)
  File "/Users/shantanu/dev/mypy/mypy/nodes.py", line 1836, in accept
    return visitor.visit_expression_stmt(self)
  File "/Users/shantanu/dev/mypy/mypy/checker.py", line 5139, in visit_expression_stmt
    expr_type = self.expr_checker.accept(s.expr, allow_none_return=True, always_allow_any=True)
  File "/Users/shantanu/dev/mypy/mypy/checkexpr.py", line 6177, in accept
    typ = node.accept(self)  # r-value type, when interpreted as a value expression
  File "/Users/shantanu/dev/mypy/mypy/nodes.py", line 2439, in accept
    return visitor.visit_name_expr(self)
           ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/checkexpr.py", line 350, in visit_name_expr
    narrowed = self.narrow_type_from_binder(e, result)
  File "/Users/shantanu/dev/mypy/mypy/checkexpr.py", line 6486, in narrow_type_from_binder
    narrowed = narrow_declared_type(known_type, restriction)
  File "/Users/shantanu/dev/mypy/mypy/meet.py", line 185, in narrow_declared_type
    elif not is_overlapping_types(declared, narrowed):
             ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/meet.py", line 379, in is_overlapping_types
    assert False, "Unexpectedly encountered partial type"
           ^^^^^
AssertionError: Unexpectedly encountered partial type