Yet another "AssertionError: Should never get here in normal mode"

[pradyunsg]

Similar crash as in #5192; happening with current pip master.

$ # In a venv with only mypy installed.
$ git clone https://github.com/pypa/pip.git --depth=1
[...]
$ cd pip
$ git fetch origin deeb1e493d8947a957c86bf256e7f5fa91c92e52
$ git checkout deeb1e493d8947a957c86bf256e7f5fa91c92e52
$ # Populate the cache; there's 2 errors as expected.
$ mypy src
[...]
$ # This run will crash
$ mypy src
Traceback (most recent call last):
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/bin/mypy", line 11, in <module>
    sys.exit(console_entry())
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/__main__.py", line 7, in console_entry
    main(None)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/main.py", line 91, in main
    res = type_check_only(sources, bin_dir, options, flush_errors, fscache)  # noqa
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/main.py", line 148, in type_check_only
    fscache=fscache)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/build.py", line 183, in build
    flush_errors, fscache)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/build.py", line 356, in _build
    graph = dispatch(sources, manager)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/build.py", line 2543, in dispatch
    process_graph(graph, manager)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/build.py", line 2833, in process_graph
    process_fresh_modules(graph, prev_scc, manager)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/build.py", line 2919, in process_fresh_modules
    graph[id].fix_cross_refs()
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/build.py", line 1927, in fix_cross_refs
    self.options.use_fine_grained_cache)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/fixup.py", line 24, in fixup_module
    node_fixer.visit_symbol_table(tree.names)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/fixup.py", line 89, in visit_symbol_table
    value.node.accept(self)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/nodes.py", line 2582, in accept
    return visitor.visit_type_alias(self)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/fixup.py", line 135, in visit_type_alias
    a.target.accept(self.type_fixer)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/types.py", line 501, in accept
    return visitor.visit_instance(self)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/fixup.py", line 149, in visit_instance
    inst.type = lookup_qualified_typeinfo(self.modules, type_ref, self.quick_and_dirty)
  File "/Users/pradyunsg/.virtualenvs/tmp-646a2fd8b91d920/lib/python3.7/site-packages/mypy/fixup.py", line 239, in lookup_qualified_typeinfo
    assert quick_and_dirty, "Should never get here in normal mode"
AssertionError: Should never get here in normal mode

I haven't tested with master (internet access is patchy for me atm) but this does occur for mypy 0.630 on Python 3.7.0.

[pradyunsg]

Doing rm -r .mypy_cache/3.7/pip/_vendor/ before a second run prevents this crash.

[ilevkivskyi]

I still see the crash on master. I am investigating now.

[ilevkivskyi]

OK, it looks like the code causing the crash is also similar to the previous one (now in urllib3):

try:  # Python 3:
    # Not a no-op, we're adding this to the namespace so it can be imported.
    ConnectionError = ConnectionError
except NameError:  # Python 2:
    class ConnectionError(Exception):
        pass

I will try to write a simple repro now.

[ilevkivskyi]

OK, the minimal repro is as simple as this:

[case testOverrideByIdemAlias]
import a
[file a.py]
import lib
x = 1
[file a.py.2]
import lib
x = 2
[file lib.py]
C = C
class C:  # type: ignore
    pass
[out]
[out2]

Also it looks like this is a regression since 0.620, caused by #5565

The fix is straightforward, the only question is does this warrant a bug-fix release 0.631?

[JukkaL]

The fix is straightforward, the only question is does this warrant a bug-fix release 0.631?

Let's wait first if there are other reports of this issue. If not, we can release 0.640 in ~two weeks, on a slightly accelerated schedule. If there are other reports, a bug-fix release may make sense.

[pradyunsg]

Thanks for this fix! ^.^

(late post)