Using members in a generic protocol leads to crash

[ptpan]

In the current master mypy crashes with the following minimal repro:

from typing import TypeVar, Generic
from typing_extensions import Protocol

_T = TypeVar("_T")

class Foo( Protocol, Generic[_T] ):
  bar: Container[_T]

class Container( Generic[_T] ):
  def __init__( s ) -> None: ...

class Bar( Foo[_T] ):
  def __init__( s ) -> None:
    s.bar = Container[_T]() # crash this line

Mypy traceback

(mypy) $ mypy generic_typevar.pyi --show-traceback
generic_typevar.pyi:15: 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: 0.730+dev.b405e05e220935dca6aa895045924ee68b435091
Traceback (most recent call last):
  File "///.virtualenvs/mypy/bin/mypy", line 10, in <module>
    sys.exit(console_entry())
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/__main__.py", line 8, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/main.py", line 83, in main
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/build.py", line 164, in build
    result = _build(sources, options, alt_lib_path, flush_errors, fscache, stdout, stderr)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/build.py", line 224, in _build
    graph = dispatch(sources, manager, stdout)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/build.py", line 2579, in dispatch
    process_graph(graph, manager)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/build.py", line 2892, in process_graph
    process_stale_scc(graph, scc, manager)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/build.py", line 2999, in process_stale_scc
    graph[id].type_check_first_pass()
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/build.py", line 2108, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 285, in check_first_pass
    self.accept(d)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 396, in accept
    stmt.accept(self)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/nodes.py", line 922, in accept
    return visitor.visit_class_def(self)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 1634, in visit_class_def
    self.accept(defn.defs)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 396, in accept
    stmt.accept(self)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/nodes.py", line 987, in accept
    return visitor.visit_block(self)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 1830, in visit_block
    self.accept(s)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 396, in accept
    stmt.accept(self)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/nodes.py", line 663, in accept
    return visitor.visit_func_def(self)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 707, in visit_func_def
    self._visit_func_def(defn)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 711, in _visit_func_def
    self.check_func_item(defn, name=defn.name())
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 773, in check_func_item
    self.check_func_def(defn, typ, name)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 952, in check_func_def
    self.accept(item.body)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 396, in accept
    stmt.accept(self)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/nodes.py", line 987, in accept
    return visitor.visit_block(self)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 1830, in visit_block
    self.accept(s)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 396, in accept
    stmt.accept(self)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/nodes.py", line 1045, in accept
    return visitor.visit_assignment_stmt(self)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 1864, in visit_assignment_stmt
    self.check_assignment(s.lvalues[-1], s.rvalue, s.type is None, s.new_syntax)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 1925, in check_assignment
    if self.check_compatibility_all_supers(lvalue, lvalue_type, rvalue):
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 2038, in check_compatibility_all_supers
    base_type, base_node = self.lvalue_type_from_base(lvalue_node, base)
  File "///.virtualenvs/mypy/lib/python3.7/site-packages/mypy/checker.py", line 2128, in lvalue_type_from_base
    assert self_type is not None, "Internal error: base lookup outside class"
AssertionError: Internal error: base lookup outside class
generic_typevar.pyi:15: : note: use --pdb to drop into pdb

[ilevkivskyi]

This has nothing to do with protocols, duplicate of #5846