NotImplementedError in map_actuals_to_formals

[The-Compiler]

When I run mypy (0.4 or git master with Python 3.5) with --check-untyped-defs over qutebrowser, I get:

Traceback (most recent call last):
  File "./.tox/mypy/bin/mypy", line 6, in <module>
    main(__file__)
  File ".../mypy/main.py", line 54, in main
    res = type_check_only(sources, bin_dir, options)
  File ".../mypy/main.py", line 102, in type_check_only
    python_path=options.python_path)
  File ".../mypy/build.py", line 209, in build
    dispatch(sources, manager)
  File ".../mypy/build.py", line 1321, in dispatch
    process_graph(graph, manager)
  File ".../mypy/build.py", line 1452, in process_graph
    process_stale_scc(graph, scc)
  File ".../mypy/build.py", line 1482, in process_stale_scc
    graph[id].type_check()
  File ".../mypy/build.py", line 1301, in type_check
    manager.type_checker.visit_file(self.tree, self.xpath)
  File ".../mypy/checker.py", line 419, in visit_file
    self.accept(d)
  File ".../mypy/checker.py", line 460, in accept
    typ = node.accept(self)
  File ".../mypy/nodes.py", line 650, in accept
    return visitor.visit_class_def(self)
  File ".../mypy/checker.py", line 1049, in visit_class_def
    self.accept(defn.defs)
  File ".../mypy/checker.py", line 460, in accept
    typ = node.accept(self)
  File ".../mypy/nodes.py", line 715, in accept
    return visitor.visit_block(self)
  File ".../mypy/checker.py", line 1144, in visit_block
    self.accept(s)
  File ".../mypy/checker.py", line 460, in accept
    typ = node.accept(self)
  File ".../mypy/nodes.py", line 531, in accept
    return visitor.visit_decorator(self)
  File ".../mypy/checker.py", line 1934, in visit_decorator
    e.func.accept(self)
  File ".../mypy/nodes.py", line 462, in accept
    return visitor.visit_func_def(self)
  File ".../mypy/checker.py", line 573, in visit_func_def
    self.check_func_item(defn, name=defn.name())
  File ".../mypy/checker.py", line 631, in check_func_item
    self.check_func_def(defn, typ, name)
  File ".../mypy/checker.py", line 739, in check_func_def
    self.accept_in_frame(item.body)
  File ".../mypy/checker.py", line 475, in accept_in_frame
    answer = self.accept(node, type_context)
  File ".../mypy/checker.py", line 460, in accept
    typ = node.accept(self)
  File ".../mypy/nodes.py", line 715, in accept
    return visitor.visit_block(self)
  File ".../mypy/checker.py", line 1144, in visit_block
    self.accept(s)
  File ".../mypy/checker.py", line 460, in accept
    typ = node.accept(self)
  File ".../mypy/nodes.py", line 753, in accept
    return visitor.visit_assignment_stmt(self)
  File ".../mypy/checker.py", line 1153, in visit_assignment_stmt
    self.check_assignment(s.lvalues[-1], s.rvalue, s.type is None)
  File ".../mypy/checker.py", line 1203, in check_assignment
    self.infer_variable_type(inferred, lvalue, self.accept(rvalue),
  File ".../mypy/checker.py", line 460, in accept
    typ = node.accept(self)
  File ".../mypy/nodes.py", line 1185, in accept
    return visitor.visit_call_expr(self)
  File ".../mypy/checker.py", line 1992, in visit_call_expr
    return self.expr_checker.visit_call_expr(e)
  File ".../mypy/checkexpr.py", line 141, in visit_call_expr
    return self.check_call_expr_with_callee_type(callee_type, e)
  File ".../mypy/checkexpr.py", line 192, in check_call_expr_with_callee_type
    e.arg_names, callable_node=e.callee)[0]
  File ".../mypy/checkexpr.py", line 226, in check_call
    lambda i: self.accept(args[i]))
  File ".../mypy/checkexpr.py", line 1570, in map_actuals_to_formals
    raise NotImplementedError()
NotImplementedError: 

*** INTERNAL ERROR ***

qutebrowser/browser/webpage.py:344: error: Internal error -- please report a bug at https://github.com/python/mypy/issues

I wasn't able to construct a minimal example which fails in the same way, but it fails on this line:

    @pyqtSlot('QWebFrame*', 'QWebPage::Feature')
    def on_feature_permission_requested(self, frame, feature):
        """Ask the user for approval for geolocation/notifications."""
        options = {
            QWebPage.Notifications: ('content', 'notifications'),
            QWebPage.Geolocation: ('content', 'geolocation'),
        }
        config_val = config.get(*options[feature])  # <-----
        # [...]

Some interesting locals from a --pdb session:

>>> argt.items
[builtins.str, builtins.str]
>>> j
1
>>> ncallee
2
>>> callee_kinds
[2, 4]

Seems like the 4 for the current argument (j=1) is nodes.UNBOUND_TVAR.

[gvanrossum]

Here's a smaller repro:

def xget(section, subsection):
    pass

def aget(*args, **kwds):
    return xget(*args, **kwds)

def foo(i):
    args = ('x', 'y')
    return aget(*args)  # <----- error

The explicit raise NotImplementedError() in the mypy code suggests that Jukka was aware that he left some complicated case unhandled. Probably not rocket science to fix it.

[refi64]

Has this been fixed already? Running Mypy on @gvanrossum's example now prints nothing.

[gvanrossum]

@The-Compiler Can you confirm? Indeed my little example doesn't crash any more. Most likely @rwbarton fixed this as a side effect of one of his other fixes.

[The-Compiler]

Unfortunately I can still reproduce this with the current master and my code - no time right now to investigate more though, sorry!

[gvanrossum]

Thanks for the confirmation! We'll keep it open. Is the code that reproduces this in your repo?

[The-Compiler]

Indeed. You should be able to clone https://github.com/The-Compiler/qutebrowser, check out the mypy branch, replace mypy-lang==0.4 by git+https://github.com/python/mypy.git in tox.ini and run tox -e mypy. When you do so, the issue will not happen because I worked around it in qutebrowser/qutebrowser@996ebbd. As soon as you do git revert 996ebbdb142070d13765d7ac619fc09553670bf1 you should see it again.

[tharvik]

I just found a smaller repro:

t = (1, 2)
'{} {}'.format(*t)

[euresti]

Here's a python2 repro we hit:

from typing import Any

def good_log(string, *n):
    # type: (str, *Any) -> None
    string %= n

def bad_log(string, *n, **kw):
    # type: (str, *Any, **Any) -> None
    string %= n

def testit():
    # type: () -> None
    good_log("Numbers: (%r %r, %r %r)", *(1, 2, 3, 4))

    bad_log("Numbers: (%r %r, %r %r)", *(1, 2, 3, 4))

Notice how the existence of the **kw is what causes this to happen.

[refi64]

Smallest test case yet:

def f(**kw): pass
f(*(1, 2))

[gvanrossum]

I'm sure this has something to do with the case analysis for "arg_kind" and the special-casing there for tuple unpacking.

[refi64]

Simply commenting out these lines seems to fix the issue and not introduce any worse bugs, though I can't be sure...

[gvanrossum]

Well, something is clearly hitting the else branch there, so the question is what the various variables are at that point. Could you come up with some test?