Semantic analysis deferral crash #11064

$ mypy .
./test1.py:2: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
If this issue continues with mypy master, please report a bug at https://github.com/python/mypy/issues
version: 0.920+dev.b17ae30d1efe58095c61c1731c29bcfe4dd7065c
./test1.py:2: : note: please use --show-traceback to print a traceback when reporting a bug
(.venv) ~/src/src mypy . --show-traceback
./test1.py:2: 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: 0.920+dev.b17ae30d1efe58095c61c1731c29bcfe4dd7065c
Traceback (most recent call last):
  File "/Users/ishimoto/src/src/.venv/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/__main__.py", line 11, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/main.py", line 87, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/main.py", line 165, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/build.py", line 179, in build
    result = _build(
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/build.py", line 254, in _build
    graph = dispatch(sources, manager, stdout)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/build.py", line 2707, in dispatch
    process_graph(graph, manager)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/build.py", line 3031, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/build.py", line 3123, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/semanal_main.py", line 78, in semantic_analysis_for_scc
    process_top_levels(graph, scc, patches)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/semanal_main.py", line 199, in process_top_levels
    deferred, incomplete, progress = semantic_analyze_target(next_id, state,
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/semanal_main.py", line 326, in semantic_analyze_target
    analyzer.refresh_partial(refresh_node,
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/semanal.py", line 402, in refresh_partial
    self.refresh_top_level(node)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/semanal.py", line 413, in refresh_top_level
    self.accept(d)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/semanal.py", line 4928, in accept
    node.accept(self)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/nodes.py", line 402, in accept
    return visitor.visit_import_all(self)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/semanal.py", line 1983, in visit_import_all
    self.add_imported_symbol(name, node, i,
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/semanal.py", line 4576, in add_imported_symbol
    self.add_symbol_table_node(name, symbol, context)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/semanal.py", line 4481, in add_symbol_table_node
    self.defer(context)
  File "/Users/ishimoto/src/src/.venv/lib/python3.9/site-packages/mypy/semanal.py", line 4639, in defer
    assert not self.final_iteration, 'Must not defer during final iteration'
AssertionError: Must not defer during final iteration
./test1.py:2: : note: use --pdb to drop into pdb

.
└── src
    ├── dir1
    │   ├── __init__.py
    │   └── test2.py
    └── test1.py