Second part of response to comments: minor things (but many); Two mor…

…e tests

docs/source/kinds_of_types.rst

@@ -427,22 +427,28 @@ assigning the type to a variable:
        ...
 
 Type aliases can be generic, in this case they could be used in two variants:
-Subscribed aliases are equivalent to original types with substituted type variables,
+Subscripted aliases are equivalent to original types with substituted type variables,
 number of type arguments must match the number of free type variables
 in generic type alias. Unsubscribed aliases are treated as original types with free
-vaiables replacec with ``Any``. Examples (following `PEP 484
+variables replaced with ``Any``. Examples (following `PEP 484
 <https://www.python.org/dev/peps/pep-0484/#type-aliases>`_):
 
 .. code-block:: python
 
     from typing import TypeVar, Iterable, Tuple, Union, Callable
     T = TypeVar('T', int, float, complex)
 
-    TInt = Tuple[T, int]
+    TInt = Tuple[int, T]
     UInt = Union[T, int]
     CBack = Callable[..., T]
     Vec = Iterable[Tuple[T, T]]
 
+    def response(query: str) -> UInt[str]:  # Same as Union[str, int]
+        ...
+    def activate(cb: CBack[T]) -> T:        # Same as Callable[..., T]
+        ...
+    table_entry: TInt  # Same as Tuple[int, Any]
+
     def inproduct(v: Vec[T]) -> T:
         return sum(x*y for x, y in v)
 
@@ -479,12 +485,9 @@ Following previous examples:
 
     A type alias does not create a new type. It's just a shorthand notation for
     another type -- it's equivalent to the target type. For generic type aliases
-    this means that variance of type variables used for alias definition does not
-    allpy to aliases. Parameterized generic alias is treated simply as an original
-    type with corresponding type variables substituted. Accordingly, type checking
-    happens when a type alias is used. Invalid aliases (like e.g.
-    ``Callable[..., List[T, T]]``) might not always be flagged by mypy if they are
-    left unused.
+    this means that variance or constraints of type variables used for alias
+    definition don't apply to aliases. Parameterized generic alias is treated
+    simply as an original type with corresponding type variables substituted.
 
 .. _newtypes:
 

mypy/checkexpr.py

@@ -1378,13 +1378,18 @@ def visit_type_application(self, tapp: TypeApplication) -> Type:
         return AnyType()
 
     def visit_type_alias_expr(self, alias: TypeAliasExpr) -> Type:
-        """ Get type of a type alias (could be generic) in a runtime expression."""
+        """Get type of a type alias (could be generic) in a runtime expression."""
         item = alias.type
-        if not alias.runtime:
+        if not alias.in_runtime:
+            # We don't replace TypeVar's with Any for alias used as Alias[T](42).
             item = self.replace_tvars_any(item)
         if isinstance(item, Instance):
+            # Normally we get a callable type (or overloaded) with .is_type_obj() true
+            # representing the class's constructor
             tp = type_object_type(item.type, self.named_type)
         else:
+            # This type is invalid in most runtime contexts
+            # and corresponding an error will be reported.
             return alias.fback
         if isinstance(tp, CallableType):
             if len(tp.variables) != len(item.args):
@@ -1403,9 +1408,9 @@ def visit_type_alias_expr(self, alias: TypeAliasExpr) -> Type:
         return AnyType()
 
     def replace_tvars_any(self, tp: Type) -> Type:
-        """ Replace all unbound type variables with Any if an alias is used in
-        a runtime expression. Basically, this function finishes what could not be done
-        in similar funtion from typeanal.py.
+        """Replace all type variables of a type alias tp with Any. Basically, this function
+        finishes what could not be done in method TypeAnalyser.visit_unbound_type()
+        from typeanal.py.
         """
         typ_args = get_typ_args(tp)
         new_args = typ_args[:]

mypy/nodes.py

@@ -1733,13 +1733,15 @@ class TypeAliasExpr(Expression):
 
     type = None  # type: mypy.types.Type
     fback = None  # type: mypy.types.Type
-    runtime = False  # type: bool
+    # This type alias is subscripted in a runtime expression like Alias[int](42)
+    # (not in a type context like type annotation or base class).
+    in_runtime = False  # type: bool
 
     def __init__(self, type: 'mypy.types.Type', fback: 'mypy.types.Type' = None,
-                 runtime: bool = False) -> None:
+                 in_runtime: bool = False) -> None:
         self.type = type
         self.fback = fback
-        self.runtime = runtime
+        self.in_runtime = in_runtime
 
     def accept(self, visitor: NodeVisitor[T]) -> T:
         return visitor.visit_type_alias_expr(self)

mypy/semanal.py

@@ -1217,7 +1217,6 @@ def alias_fallback(self, tp: Type) -> Instance:
         """Make a dummy Instance with no methods. It is used as a fallback type
         to detect errors for non-Instance aliases (i.e. Unions, Tuples, Callables).
         """
-
         kind = (' to Callable' if isinstance(tp, CallableType) else
                 ' to Tuple' if isinstance(tp, TupleType) else
                 ' to Union' if isinstance(tp, UnionType) else '')
@@ -2378,13 +2377,13 @@ def visit_unary_expr(self, expr: UnaryExpr) -> None:
     def visit_index_expr(self, expr: IndexExpr) -> None:
         expr.base.accept(self)
         if isinstance(expr.base, RefExpr) and expr.base.kind == TYPE_ALIAS:
-            # Special form -- subcribing a generic type alias.
+            # Special form -- subscripting a generic type alias.
             # Perform the type substitution and create a new alias.
             res = analyze_type_alias(expr,
                                      self.lookup_qualified,
                                      self.lookup_fully_qualified,
                                      self.fail)
-            expr.analyzed = TypeAliasExpr(res, fback=self.alias_fallback(res), runtime=True)
+            expr.analyzed = TypeAliasExpr(res, fback=self.alias_fallback(res), in_runtime=True)
         elif refers_to_class_or_function(expr.base):
             # Special form -- type application.
             # Translate index to an unanalyzed type.

mypy/typeanal.py

@@ -79,7 +79,7 @@ def __init__(self,
                  lookup_func: Callable[[str, Context], SymbolTableNode],
                  lookup_fqn_func: Callable[[str], SymbolTableNode],
                  fail_func: Callable[[str, Context], None], *,
-                 aliasing = False) -> None:
+                 aliasing: bool = False) -> None:
         self.lookup = lookup_func
         self.lookup_fqn_func = lookup_fqn_func
         self.fail = fail_func
@@ -158,8 +158,6 @@ def visit_unbound_type(self, t: UnboundType) -> Type:
                 if exp_len == 0 and act_len == 0:
                     return override
                 if act_len != exp_len:
-                    # TODO: Detect wrong type variable numer for unused aliases
-                    # (it is difficult at this stage, see comment below, line 187 atm)
                     self.fail('Bad number of arguments for type alias, expected: %s, given: %s'
                               % (exp_len, act_len), t)
                     return t
@@ -174,7 +172,7 @@ def visit_unbound_type(self, t: UnboundType) -> Type:
                     # as a base class -- however, this will fail soon at runtime so the problem
                     # is pretty minor.
                     return AnyType()
-                # Allow unbount type variables when defining an alias
+                # Allow unbound type variables when defining an alias
                 if not (self.aliasing and sym.kind == UNBOUND_TVAR):
                     self.fail('Invalid type "{}"'.format(name), t)
                 return t
@@ -205,7 +203,7 @@ def visit_unbound_type(self, t: UnboundType) -> Type:
             return AnyType()
 
     def get_type_var_names(self, tp: Type) -> List[str]:
-        """ Get all type variable names that are present in a generic type alias
+        """Get all type variable names that are present in a generic type alias
         in order of textual appearance (recursively, if needed).
         """
         tvars = []  # type: List[str]
@@ -236,7 +234,7 @@ def get_tvar_name(self, t: Type) -> Optional[str]:
         return None
 
     def replace_alias_tvars(self, tp: Type, vars: List[str], subs: List[Type]) -> Type:
-        """ Replace type variables in a generic type alias tp with substitutions subs.
+        """Replace type variables in a generic type alias tp with substitutions subs.
         Length of subs should be already checked.
         """
         typ_args = get_typ_args(tp)

mypy/types.py

@@ -1527,6 +1527,7 @@ def function_type(func: mypy.nodes.FuncBase, fallback: Instance) -> FunctionLike
 
 
 def get_typ_args(tp: Type) -> List[Type]:
+    """Get all type arguments from a parameterizable Type."""
     if not isinstance(tp, (Instance, UnionType, TupleType, CallableType)):
         return []
     typ_args = (tp.args if isinstance(tp, Instance) else
@@ -1536,12 +1537,13 @@ def get_typ_args(tp: Type) -> List[Type]:
 
 
 def set_typ_args(tp: Type, new_args: List[Type]) -> Type:
+    """Return a copy of a parameterizable Type with arguments set to new_args."""
     if isinstance(tp, Instance):
-        return Instance(tp.type, new_args, tp.line)
+        return Instance(tp.type, new_args, tp.line, tp.column)
     if isinstance(tp, TupleType):
         return tp.copy_modified(items=new_args)
     if isinstance(tp, UnionType):
-        return UnionType.make_union(new_args, tp.line)
+        return UnionType.make_simplified_union(new_args, tp.line, tp.column)
     if isinstance(tp, CallableType):
         return tp.copy_modified(arg_types=new_args[:-1], ret_type=new_args[-1])
     return tp

test-data/unit/check-generics.test

@@ -766,7 +766,7 @@ if not isinstance(s, str):
 
 z = None # type: TNode # Same as TNode[Any]
 z.x
-z.foo() # E: Some element of union has no attribute "foo"
+z.foo() # Any simplyfies Union to Any
 
 [builtins fixtures/isinstance.pyi]
 
@@ -914,6 +914,44 @@ reveal_type(us) # E: Revealed type is 'Any'
 
 [out]
 
+[case testGenericTypeAliasesTypeVarBinding]
+from typing import TypeVar, Generic, List
+T = TypeVar('T')
+S = TypeVar('S')
+
+class A(Generic[T, S]):
+    def __init__(self, x: T, y: S) -> None: ...
+
+class B(Generic[T, S]):
+    def __init__(self, x: List[T], y: List[S]) -> None: ...
+
+SameA = A[T, T]
+SameB = B[T, T]
+
+class C(Generic[T]):
+    a = None # type: SameA[T]
+    b = SameB[T]([], [])
+
+reveal_type(C[int]().a) # E: Revealed type is '__main__.A[builtins.int*, builtins.int*]'
+reveal_type(C[str]().b) # E: Revealed type is '__main__.B[builtins.str*, builtins.str*]'
+
+[builtins fixtures/list.pyi]
+
+[case testGenericTypeAliasesTypeVarConstraints]
+from typing import TypeVar, Generic
+T = TypeVar('T', int, list)
+S = TypeVar('S', int, list)
+
+class A(Generic[T, S]):
+    def __init__(self, x: T, y: S) -> None: ...
+
+BadA = A[str, T] # E: Bad ...
+SameA = A[T, T]
+
+x = None # type: SameA[int]
+y = None # type: SameA[str] # E: Bad ...
+
+[builtins fixtures/list.pyi]
 
 -- Multiple assignment with lists
 -- ------------------------------