classmethod of Generic class fail with TypeVarType is already analyzed

[tharvik]

Stacktrack very closely related to #1682, but unable to find a way to related both issues.

from typing import TypeVar, Generic

T = TypeVar('T')

class A(Generic[T]):
    def __init__(self, a: T) -> None: ...
    @classmethod
    def f(cls) -> None: ...

gives

*** INTERNAL ERROR ***
asd4.py:7: error: Internal error -- please report a bug at https://github.com/python/mypy/issues
NOTE: you can use "mypy --pdb ..." to drop into the debugger when this happens.
Traceback (most recent call last):
  File "/usr/lib/python-exec/python3.4/mypy", line 6, in <module>
    main(__file__)
  File "/usr/lib64/python3.4/site-packages/mypy/main.py", line 40, in main
    res = type_check_only(sources, bin_dir, options)
  File "/usr/lib64/python3.4/site-packages/mypy/main.py", line 81, in type_check_only
    options=options)
  File "/usr/lib64/python3.4/site-packages/mypy/build.py", line 177, in build
    dispatch(sources, manager)
  File "/usr/lib64/python3.4/site-packages/mypy/build.py", line 1331, in dispatch
    process_graph(graph, manager)
  File "/usr/lib64/python3.4/site-packages/mypy/build.py", line 1469, in process_graph
    process_stale_scc(graph, scc)
  File "/usr/lib64/python3.4/site-packages/mypy/build.py", line 1542, in process_stale_scc
    graph[id].semantic_analysis()
  File "/usr/lib64/python3.4/site-packages/mypy/build.py", line 1296, in semantic_analysis
    self.manager.semantic_analyzer.visit_file(self.tree, self.xpath)
  File "/usr/lib64/python3.4/site-packages/mypy/semanal.py", line 243, in visit_file
    self.accept(d)
  File "/usr/lib64/python3.4/site-packages/mypy/semanal.py", line 2306, in accept
    node.accept(self)
  File "/usr/lib64/python3.4/site-packages/mypy/nodes.py", line 660, in accept
    return visitor.visit_class_def(self)
  File "/usr/lib64/python3.4/site-packages/mypy/semanal.py", line 564, in visit_class_def
    defn.defs.accept(self)
  File "/usr/lib64/python3.4/site-packages/mypy/nodes.py", line 723, in accept
    return visitor.visit_block(self)
  File "/usr/lib64/python3.4/site-packages/mypy/semanal.py", line 1014, in visit_block
    self.accept(s)
  File "/usr/lib64/python3.4/site-packages/mypy/semanal.py", line 2306, in accept
    node.accept(self)
  File "/usr/lib64/python3.4/site-packages/mypy/nodes.py", line 544, in accept
    return visitor.visit_decorator(self)
  File "/usr/lib64/python3.4/site-packages/mypy/semanal.py", line 1626, in visit_decorator
    dec.func.accept(self)
  File "/usr/lib64/python3.4/site-packages/mypy/nodes.py", line 475, in accept
    return visitor.visit_func_def(self)
  File "/usr/lib64/python3.4/site-packages/mypy/semanal.py", line 316, in visit_func_def
    self.analyze_function(defn)
  File "/usr/lib64/python3.4/site-packages/mypy/semanal.py", line 468, in analyze_function
    defn.type = self.anal_type(defn.type)
  File "/usr/lib64/python3.4/site-packages/mypy/semanal.py", line 1039, in anal_type
    return t.accept(a)
  File "/usr/lib64/python3.4/site-packages/mypy/types.py", line 606, in accept
    return visitor.visit_callable_type(self)
  File "/usr/lib64/python3.4/site-packages/mypy/typeanal.py", line 204, in visit_callable_type
    return t.copy_modified(arg_types=self.anal_array(t.arg_types),
  File "/usr/lib64/python3.4/site-packages/mypy/typeanal.py", line 274, in anal_array
    res.append(t.accept(self))
  File "/usr/lib64/python3.4/site-packages/mypy/types.py", line 606, in accept
    return visitor.visit_callable_type(self)
  File "/usr/lib64/python3.4/site-packages/mypy/typeanal.py", line 204, in visit_callable_type
    return t.copy_modified(arg_types=self.anal_array(t.arg_types),
  File "/usr/lib64/python3.4/site-packages/mypy/typeanal.py", line 274, in anal_array
    res.append(t.accept(self))
  File "/usr/lib64/python3.4/site-packages/mypy/types.py", line 448, in accept
    return visitor.visit_type_var(self)
  File "/usr/lib64/python3.4/site-packages/mypy/typeanal.py", line 201, in visit_type_var
    raise RuntimeError('TypeVarType is already analyzed')
RuntimeError: TypeVarType is already analyzed

Removing the Generic subclassing also triggers it.

[gvanrossum]

Looking into this, but making slow progress. I just rediscovered that removing Generic[T] from the base still triggers this. The immediate cause seems to be that the type of cls in the class method is derived from the constructor signature, but apparently if that contains type variables it always thinks it's a generic function, and that always causes this crash.

So there are really two bugs -- the crash when the constructor is actually a generic function; and the way the cls type believes the constructor is a generic function even when its type variable belongs to the class.

[gvanrossum]

My best guess is that the raise causing this crash was wrong.