Crash unpacking tuple in argument list

[scott-ainsworth]

The following code produces a NotImplementedError using Python 3.5.2 and mypy 0.4.2-dev (commit commit e7e9c4a):

from typing import Any, List, Optional, Tuple

def count(items: Optional[List[Any]]) -> Tuple[int, str]:
    """Return item count and English singular/plural ('' or 's')."""
    if not items:
        return 0, 's'
    count = len(items)
    return count, '' if count == 1 else 's'

items = [1, 2, 3]
print('{0} items{1}'.format(*count(items)))

Here is the command line and stack dump:

$ mypy --disallow-untyped-defs --disallow-untyped-calls mypy-failure.py
Traceback (most recent call last):
  File "/Volumes/Research/python35-venv/bin/mypy", line 6, in <module>
    main(__file__)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/main.py", line 54, in main
    res = type_check_only(sources, bin_dir, options)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/main.py", line 102, in type_check_only
    python_path=options.python_path)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/build.py", line 209, in build
    dispatch(sources, manager)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/build.py", line 1329, in dispatch
    process_graph(graph, manager)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/build.py", line 1460, in process_graph
    process_stale_scc(graph, scc)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/build.py", line 1490, in process_stale_scc
    graph[id].type_check()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/build.py", line 1309, in type_check
    manager.type_checker.visit_file(self.tree, self.xpath)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checker.py", line 424, in visit_file
    self.accept(d)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checker.py", line 465, in accept
    typ = node.accept(self)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/nodes.py", line 729, in accept
    return visitor.visit_expression_stmt(self)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checker.py", line 1570, in visit_expression_stmt
    self.accept(s.expr)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checker.py", line 465, in accept
    typ = node.accept(self)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/nodes.py", line 1185, in accept
    return visitor.visit_call_expr(self)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checker.py", line 1993, in visit_call_expr
    return self.expr_checker.visit_call_expr(e)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checkexpr.py", line 141, in visit_call_expr
    return self.check_call_expr_with_callee_type(callee_type, e)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checkexpr.py", line 192, in check_call_expr_with_callee_type
    e.arg_names, callable_node=e.callee)[0]
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checkexpr.py", line 235, in check_call
    callee, args, arg_kinds, formal_to_actual)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checkexpr.py", line 330, in infer_arg_types_in_context2
    res[ai] = self.accept(args[ai], callee.arg_types[i])
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checkexpr.py", line 1491, in accept
    return self.chk.accept(node, context)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checker.py", line 465, in accept
    typ = node.accept(self)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/nodes.py", line 1185, in accept
    return visitor.visit_call_expr(self)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checker.py", line 1993, in visit_call_expr
    return self.expr_checker.visit_call_expr(e)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checkexpr.py", line 141, in visit_call_expr
    return self.check_call_expr_with_callee_type(callee_type, e)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checkexpr.py", line 192, in check_call_expr_with_callee_type
    e.arg_names, callable_node=e.callee)[0]
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checkexpr.py", line 226, in check_call
    lambda i: self.accept(args[i]))
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/mypy/checkexpr.py", line 1589, in map_actuals_to_formals
    raise NotImplementedError()
NotImplementedError:

*** INTERNAL ERROR ***```

[refi64]

Duplicate of #1553?

[scott-ainsworth]

Oops, sure looks like it.