Fallback type for namedtuple/NamedTuple has containing module as module name

[gvanrossum]

Example:

from typing import NamedTuple

F = [('x', int)]
A = NamedTuple('A', F)  # List or tuple literal expected as the second argument to namedtuple()

def f(a: A):
    reveal_type(a)  # Revealed type is 'Tuple[, fallback=t.namedtuple]'

The first error is expected. But when we silence it, we see that the fallback type generated in this case is not collections.namedtuple but t.namedtuple (t.py was the filename I used).

The problem is that the fallback type ends up in the incremental cache, resulting in tracebacks when incremental mode is used like this:

Traceback (most recent call last):
  File "/usr/lib/python3.5/runpy.py", line 184, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.5/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/user/src/server/.mypy/venv/lib/python3.5/site-packages/mypy/__main__.py", line 11, in <module>
    main(None)
  File "/home/user/src/server/.mypy/venv/lib/python3.5/site-packages/mypy/main.py", line 66, in main
    res = type_check_only(sources, bin_dir, options)
  File "/home/user/src/server/.mypy/venv/lib/python3.5/site-packages/mypy/main.py", line 119, in type_check_only
    options=options)
  File "/home/user/src/server/.mypy/venv/lib/python3.5/site-packages/mypy/build.py", line 212, in build
    graph = dispatch(sources, manager)
  File "/home/user/src/server/.mypy/venv/lib/python3.5/site-packages/mypy/build.py", line 1939, in dispatch
    process_graph(graph, manager)
  File "/home/user/src/server/.mypy/venv/lib/python3.5/site-packages/mypy/build.py", line 2219, in process_graph
    process_fresh_scc(graph, prev_scc, manager)
  File "/home/user/src/server/.mypy/venv/lib/python3.5/site-packages/mypy/build.py", line 2296, in process_fresh_scc
    graph[id].fix_cross_refs()
  File "/home/user/src/server/.mypy/venv/lib/python3.5/site-packages/mypy/build.py", line 1656, in fix_cross_refs
    self.manager.options.quick_and_dirty)
  File "/home/user/src/server/.mypy/venv/lib/python3.5/site-packages/mypy/fixup.py", line 22, in fixup_module_pass_one
    node_fixer.visit_symbol_table(tree.names)
  File "/home/user/src/server/.mypy/venv/lib/python3.5/site-packages/mypy/fixup.py", line 84, in visit_symbol_table
    self.quick_and_dirty)
  File "/home/user/src/server/.mypy/venv/lib/python3.5/site-packages/mypy/fixup.py", line 284, in lookup_qualified_stnode
    assert key in names, "Cannot find %s for %s" % (key, name)
AssertionError: Cannot find namedtuple for metaserver.lib.deletion_filter.namedtuple

[gvanrossum]

(Note I don't have an exact recipe for the crash, but it's clearly related.)