

-- Basic test cases
-- ----------------


[case testBasicContextInference]
from typing import TypeVar, Generic
T = TypeVar('T')

def f() -> 'A[T]': pass

class A(Generic[T]): pass
class B: pass

ab: A[B]
ao: A[object]
b: B

if int():
    ao = f()
if int():
    ab = f()
if int():
    b = f() # E: Incompatible types in assignment (expression has type "A[<nothing>]", variable has type "B")
[case testBasicContextInferenceForConstructor]
from typing import TypeVar, Generic
T = TypeVar('T')
class A(Generic[T]): pass
class B: pass
ab: A[B]
ao: A[object]
b: B

if int():
    ao = A()
if int():
    ab = A()
if int():
    b = A() # E: Incompatible types in assignment (expression has type "A[<nothing>]", variable has type "B")
[case testIncompatibleContextInference]
from typing import TypeVar, Generic
T = TypeVar('T')
def f(a: T) -> 'A[T]':
    pass

class A(Generic[T]): pass

class B: pass
class C: pass
b: B
c: C
ab: A[B]
ao: A[object]
ac: A[C]

if int():
    ac = f(b) # E: Argument 1 to "f" has incompatible type "B"; expected "C"
if int():
    ab = f(c) # E: Argument 1 to "f" has incompatible type "C"; expected "B"

if int():
    ao = f(b)
if int():
    ab = f(b)
if int():
    ao = f(c)
if int():
    ac = f(c)


-- Local variables
-- ---------------


[case testInferGenericLocalVariableTypeWithEmptyContext]
from typing import TypeVar, Generic
T = TypeVar('T')
def g() -> None:
    ao: A[object]
    ab: A[B]
    o: object
    b: B

    x = f(o)
    if int():
        ab = x # E: Incompatible types in assignment (expression has type "A[object]", variable has type "A[B]")
        ao = x
    y = f(b)
    if int():
        ao = y # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[object]")
        ab = y

def f(a: T) -> 'A[T]': pass

class A(Generic[T]): pass
class B: pass
[out]

[case testInferLocalVariableTypeWithUnderspecifiedGenericType]
from typing import TypeVar, Generic
T = TypeVar('T')
def g() -> None:
    x = f() # E: Need type annotation for "x"

def f() -> 'A[T]': pass
class A(Generic[T]): pass
[out]

[case testInferMultipleLocalVariableTypesWithTupleRvalue]
from typing import TypeVar, Generic
T = TypeVar('T')
def g() -> None:
    ao: A[object]
    ab: A[B]
    b: B
    x, y = f(b), f(b)
    if int():
        ao = x # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[object]")
        ao = y # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[object]")
        ab = x
        ab = y

def f(a: T) -> 'A[T]': pass
class A(Generic[T]): pass
class B: pass
[out]

[case testInferMultipleLocalVariableTypesWithArrayRvalueAndNesting]
from typing import TypeVar, List, Generic
T = TypeVar('T')
def h() -> None:
    ao: A[object]
    ab: A[B]
    b: B
    x, y = g(f(b))
    if int():
        ao = x # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[object]")
        ao = y # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[object]")
        ab = x
        ab = y

def f(a: T) -> 'A[T]': pass
def g(a: T) -> List[T]: pass

class A(Generic[T]): pass
class B: pass
[builtins fixtures/for.pyi]
[out]


-- Return types with multiple tvar instances
-- -----------------------------------------


[case testInferenceWithTypeVariableTwiceInReturnType]
from typing import TypeVar, Tuple, Generic
T = TypeVar('T')

def f(a: T) -> 'Tuple[A[T], A[T]]': pass

class A(Generic[T]): pass
class B: pass

b: B
o: object
ab: A[B]
ao: A[object]

if int():
    ab, ao = f(b) # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[object]")
if int():
    ao, ab = f(b) # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[object]")

if int():
    ao, ao = f(b)
if int():
    ab, ab = f(b)
if int():
    ao, ao = f(o)
[builtins fixtures/tuple.pyi]

[case testInferenceWithTypeVariableTwiceInReturnTypeAndMultipleVariables]
from typing import TypeVar, Tuple, Generic
S = TypeVar('S')
T = TypeVar('T')

def f(a: S, b: T) -> 'Tuple[A[S], A[T], A[T]]': pass
def g(a: S, b: T) -> 'Tuple[A[S], A[S], A[T]]': pass
def h(a: S, b: T) -> 'Tuple[A[S], A[S], A[T], A[T]]': pass

class A(Generic[T]): pass
class B: pass

b: B
o: object
ab: A[B]
ao: A[object]

if int():
    ao, ao, ab = f(b, b)     # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[object]")
if int():
    ao, ab, ao = g(b, b)     # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[object]")
if int():
    ao, ab, ab, ab = h(b, b) # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[object]")
if int():
    ab, ab, ao, ab = h(b, b) # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[object]")

if int():
    ao, ab, ab = f(b, b)
if int():
    ab, ab, ao = g(b, b)
if int():
    ab, ab, ab, ab = h(b, b)
[builtins fixtures/tuple.pyi]


-- Multiple tvar instances in arguments
-- ------------------------------------


[case testMultipleTvatInstancesInArgs]
from typing import TypeVar, Generic
T = TypeVar('T')

def f(a: T, b: T) -> 'A[T]': pass

class A(Generic[T]): pass
class B: pass
class C(B): pass

ac: A[C]
ab: A[B]
ao: A[object]
b: B
c: C
o: object

if int():
    ab = f(b, o) # E: Argument 2 to "f" has incompatible type "object"; expected "B"
if int():
    ab = f(o, b) # E: Argument 1 to "f" has incompatible type "object"; expected "B"
if int():
    ac = f(b, c) # E: Argument 1 to "f" has incompatible type "B"; expected "C"
if int():
    ac = f(c, b) # E: Argument 2 to "f" has incompatible type "B"; expected "C"

if int():
    ao = f(b, c)
if int():
    ao = f(c, b)
if int():
    ab = f(c, b)


-- Nested generic function calls
-- -----------------------------


[case testNestedGenericFunctionCall1]
from typing import TypeVar, Generic
T = TypeVar('T')

def f(a: T) -> 'A[T]': pass

class A(Generic[T]): pass
class B: pass

aab: A[A[B]]
aao: A[A[object]]
ao: A[object]
b: B
o: object

if int():
    aab = f(f(o)) # E: Argument 1 to "f" has incompatible type "object"; expected "B"

if int():
    aab = f(f(b))
    aao = f(f(b))
    ao = f(f(b))

[case testNestedGenericFunctionCall2]
from typing import TypeVar, Generic
T = TypeVar('T')

def f(a: T) -> T: pass
def g(a: T) -> 'A[T]': pass

class A(Generic[T]): pass
class B: pass

ab: A[B]
ao: A[object]
b: B
o: object

if int():
    ab = f(g(o)) # E: Argument 1 to "g" has incompatible type "object"; expected "B"

if int():
    ab = f(g(b))
    ao = f(g(b))

[case testNestedGenericFunctionCall3]
from typing import TypeVar, Generic
T = TypeVar('T')
def f(a: T, b: T) -> T:
    pass

def g(a: T) -> 'A[T]': pass

class A(Generic[T]): pass
class B: pass
ab: A[B]
ao: A[object]
b: B
o: object

if int():
    ab = f(g(o), g(b)) # E: Argument 1 to "g" has incompatible type "object"; expected "B"
if int():
    ab = f(g(b), g(o)) # E: Argument 1 to "g" has incompatible type "object"; expected "B"

if int():
    ab = f(g(b), g(b))
    ao = f(g(b), g(o))
if int():
    ao = f(g(o), g(b))


-- Method calls
-- ------------


[case testMethodCallWithContextInference]
from typing import TypeVar, Generic
T = TypeVar('T')
o: object
b: B
c: C
def f(a: T) -> 'A[T]': pass

class A(Generic[T]):
    def g(self, a: 'A[T]') -> 'A[T]': pass

class B: pass
class C(B): pass
ao: A[object]
ab: A[B]
ac: A[C]

ab.g(f(o))        # E: Argument 1 to "f" has incompatible type "object"; expected "B"
if int():
    ac = f(b).g(f(c)) # E: Incompatible types in assignment (expression has type "A[B]", variable has type "A[C]")
if int():
    ac = f(c).g(f(b)) # E: Argument 1 to "f" has incompatible type "B"; expected "C"

if int():
    ab = f(b).g(f(c))
ab.g(f(c))


-- List expressions
-- ----------------


[case testEmptyListExpression]
from typing import List
aa: List[A]
ao: List[object]
a: A
def f(): a, aa, ao # Prevent redefinition

a = [] # E: Incompatible types in assignment (expression has type "List[<nothing>]", variable has type "A")

aa = []
ao = []

class A: pass
[builtins fixtures/list.pyi]

[case testSingleItemListExpressions]
from typing import List, Optional
aa: List[Optional[A]]
ab: List[B]
ao: List[object]
a: A
b: B
def f(): aa, ab, ao # Prevent redefinition

aa = [b] # E: List item 0 has incompatible type "B"; expected "Optional[A]"
ab = [a] # E: List item 0 has incompatible type "A"; expected "B"

aa = [a]
ab = [b]
ao = [a]
aa = [None]
ao = [None]

class A: pass
class B: pass
[builtins fixtures/list.pyi]

[case testMultiItemListExpressions]
from typing import List
aa: List[A]
ab: List[B]
ao: List[object]
a: A
b: B
def f(): ab, aa, ao # Prevent redefinition

ab = [b, a] # E: List item 1 has incompatible type "A"; expected "B"
ab = [a, b] # E: List item 0 has incompatible type "A"; expected "B"

aa = [a, b, a]
ao = [a, b]

class A: pass
class B(A): pass
[builtins fixtures/list.pyi]

[case testLocalVariableInferenceFromEmptyList]
import typing
def f() -> None:
    a = []     # E: Need type annotation for "a" (hint: "a: List[<type>] = ...")
    b = [None]
    c = [B()]
    if int():
        c = [object()] # E: List item 0 has incompatible type "object"; expected "B"
        c = [B()]
class B: pass
[builtins fixtures/list.pyi]
[out]

[case testNestedListExpressions]
# flags: --no-strict-optional
from typing import List
aao = None # type: List[List[object]]
aab = None # type: List[List[B]]
ab = None # type: List[B]
b = None # type: B
o = None # type: object
def f(): aao, aab # Prevent redefinition

aao = [[o], ab] # E: List item 1 has incompatible type "List[B]"; expected "List[object]"
aab = [[], [o]] # E: List item 0 has incompatible type "object"; expected "B"

aao = [[None], [b], [], [o]]
aab = [[None], [b], []]
aab = [ab, []]

class B: pass
[builtins fixtures/list.pyi]


-- Complex context
-- ---------------


[case testParenthesesAndContext]
from typing import List
class A: pass
l = ([A()]) # type: List[object]
[builtins fixtures/list.pyi]

[case testComplexTypeInferenceWithTuple]
from typing import TypeVar, Tuple, Generic
k = TypeVar('k')
t = TypeVar('t')
v = TypeVar('v')

class A(Generic[t]): pass
class B: pass
class C: pass
class D(Generic[k, v]): pass

def f(x: Tuple[k]) -> 'A[k]': pass

d = f((A(),)) # type: A[A[B]]
[builtins fixtures/list.pyi]


-- Dictionary literals
-- -------------------


[case testDictionaryLiteralInContext]
from typing import Dict, TypeVar, Generic
t = TypeVar('t')
class A(Generic[t]): pass
class B: pass
class C: pass
a_b = A() # type: A[B]
a_c = A() # type: A[C]
d = {A() : a_c,
     a_b : A()} # type: Dict[A[B], A[C]]
[builtins fixtures/dict.pyi]


-- Special cases (regression tests etc.)
-- -------------------------------------


[case testInitializationWithInferredGenericType]
from typing import TypeVar, Generic
T = TypeVar('T')

def f(x: T) -> T: pass
class C(Generic[T]): pass
class A: pass

c = f(A()) # type: C[A] # E: Argument 1 to "f" has incompatible type "A"; expected "C[A]"
[case testInferredGenericTypeAsReturnValue]
from typing import TypeVar, Generic
T = TypeVar('T')
def t() -> 'A[B]':
    return f(D()) # E: Argument 1 to "f" has incompatible type "D"; expected "B"
    return A()
    return f(C())

def f(a: T) -> 'A[T]': pass
class A(Generic[T]): pass
class B: pass
class C(B): pass
class D: pass
[out]

[case testIntersectionWithInferredGenericArgument]
from foo import *
[file foo.pyi]
from typing import overload, TypeVar, Generic
T = TypeVar('T')
f(A())

@overload
def f(x: 'A[B]') -> None: pass
@overload
def f(x: 'B') -> None: pass
class A(Generic[T]): pass
class B: pass

[case testInferenceWithAbstractClassContext]
from typing import TypeVar, Generic
from abc import abstractmethod, ABCMeta
t = TypeVar('t')

class I(Generic[t]):
    @abstractmethod
    def f(self): pass
class A(I[t], Generic[t]):
    def f(self): pass

x = A() # type: I[int]
a_object = A() # type: A[object]
y = a_object # type: I[int] # E: Incompatible types in assignment (expression has type "A[object]", variable has type "I[int]")

[case testInferenceWithAbstractClassContext2]
from typing import TypeVar, Generic
from abc import abstractmethod, ABCMeta
t = TypeVar('t')
class I(Generic[t]): pass
class A(I[t], Generic[t]): pass
def f(i: I[t]) -> A[t]: pass
a = f(A()) # type: A[int]
a_int = A() # type: A[int]
aa = f(a_int)

[case testInferenceWithAbstractClassContext3]
from typing import TypeVar, Generic, Iterable
t = TypeVar('t')
class set(Generic[t]):
    def __init__(self, iterable: Iterable[t]) -> None: pass
b = bool()
l = set([b])
if int():
    l = set([object()]) # E: List item 0 has incompatible type "object"; expected "bool"
[builtins fixtures/for.pyi]


-- Infer generic type in 'Any' context
-- -----------------------------------


[case testInferGenericTypeInAnyContext]
from typing import Any, TypeVar, Generic
s = TypeVar('s')
t = TypeVar('t')
class C(Generic[s, t]): pass
x = [] # type: Any
y = C() # type: Any
[builtins fixtures/list.pyi]


-- Lambdas
-- -------


[case testInferLambdaArgumentTypeUsingContext]
from typing import Callable
f: Callable[[B], A]
if int():
    f = lambda x: x.o
    f = lambda x: x.x # E: "B" has no attribute "x"
class A: pass
class B:
  o: A

[case testInferLambdaReturnTypeUsingContext]
from typing import List, Callable
f: Callable[[], List[A]]
if int():
    f = lambda: []
    f = lambda: [B()]  # E: List item 0 has incompatible type "B"; expected "A"
class A: pass
class B: pass
[builtins fixtures/list.pyi]

[case testInferLambdaTypeUsingContext]
x : str = (lambda x: x + 1)(1)  # E: Incompatible types in assignment (expression has type "int", variable has type "str")
reveal_type((lambda x, y: x + y)(1, 2))  # N: Revealed type is "builtins.int"
(lambda x, y: x + y)(1, "")  # E: Unsupported operand types for + ("int" and "str")
(lambda *, x, y: x + y)(x=1, y="")  # E: Unsupported operand types for + ("int" and "str")
reveal_type((lambda s, i: s)(i=0, s='x')) # N: Revealed type is "Literal['x']?"
reveal_type((lambda s, i: i)(i=0, s='x')) # N: Revealed type is "Literal[0]?"
reveal_type((lambda x, s, i: x)(1.0, i=0, s='x')) # N: Revealed type is "builtins.float"
(lambda x, s, i: x)() # E: Too few arguments
(lambda: 0)(1) # E: Too many arguments
-- varargs are not handled, but it should not crash
reveal_type((lambda *k, s, i: i)(type, i=0, s='x')) # N: Revealed type is "Any"
reveal_type((lambda s, *k, i: i)(i=0, s='x')) # N: Revealed type is "Any"
reveal_type((lambda s, i, **k: i)(i=0, s='x')) # N: Revealed type is "Any"
[builtins fixtures/dict.pyi]

[case testInferLambdaAsGenericFunctionArgument]
from typing import TypeVar, List, Any, Callable
t = TypeVar('t')
class A:
  x = None # type: A
def f(a: List[t], fn: Callable[[t], Any]) -> None: pass
list_a = [] # type: List[A]
f(list_a, lambda a: a.x)
[builtins fixtures/list.pyi]

[case testLambdaWithoutContext]
reveal_type(lambda x: x)  # N: Revealed type is "def (x: Any) -> Any"
reveal_type(lambda x: 1)  # N: Revealed type is "def (x: Any) -> Literal[1]?"

[case testLambdaContextVararg]
from typing import Callable
def f(t: Callable[[str], str]) -> str: ''
f(lambda *_: '')
[builtins fixtures/tuple.pyi]

[case testInvalidContextForLambda]
from typing import Callable
f = lambda x: A() # type: Callable[[], A]
f2 = lambda: A() # type: Callable[[A], A]
class A: pass
[out]
main:2: error: Cannot infer type of lambda
main:2: error: Incompatible types in assignment (expression has type "Callable[[Any], A]", variable has type "Callable[[], A]")
main:3: error: Cannot infer type of lambda
main:3: error: Incompatible types in assignment (expression has type "Callable[[], A]", variable has type "Callable[[A], A]")

[case testEllipsisContextForLambda]
from typing import Callable
f1 = lambda x: 1 # type: Callable[..., int]
f2 = lambda: 1 # type: Callable[..., int]
f3 = lambda *args, **kwargs: 1 # type: Callable[..., int]
f4 = lambda x: x # type: Callable[..., int]
g = lambda x: 1 # type: Callable[..., str]
[builtins fixtures/dict.pyi]
[out]
main:6: error: Incompatible types in assignment (expression has type "Callable[[Any], int]", variable has type "Callable[..., str]")
main:6: error: Incompatible return value type (got "int", expected "str")

[case testEllipsisContextForLambda2]
from typing import TypeVar, Callable
T = TypeVar('T')
def foo(arg: Callable[..., T]) -> None: pass
foo(lambda: 1)

[case testLambdaNoneInContext]
# flags: --no-strict-optional
from typing import Callable
def f(x: Callable[[], None]) -> None: pass
def g(x: Callable[[], int]) -> None: pass
f(lambda: None)
g(lambda: None)

[case testIsinstanceInInferredLambda]
from typing import TypeVar, Callable, Optional
T = TypeVar('T')
S = TypeVar('S')
class A: pass
class B(A): pass
class C(A): pass
def f(func: Callable[[T], S], *z: T, r: Optional[S] = None) -> S: pass
f(lambda x: 0 if isinstance(x, B) else 1) # E: Cannot infer type argument 1 of "f"
f(lambda x: 0 if isinstance(x, B) else 1, A())() # E: "int" not callable
f(lambda x: x if isinstance(x, B) else B(), A(), r=B())() # E: "B" not callable
f(
    lambda x:  # E: Argument 1 to "f" has incompatible type "Callable[[A], A]"; expected "Callable[[A], B]"
        B() if isinstance(x, B) else x, # E: Incompatible return value type (got "A", expected "B")
    A(), r=B())
[builtins fixtures/isinstance.pyi]


-- Overloads + generic functions
-- -----------------------------


[case testMapWithOverloadedFunc]
from foo import *
[file foo.pyi]
from typing import TypeVar, Callable, List, overload, Any
t = TypeVar('t')
s = TypeVar('s')
def map(f: Callable[[t], s], seq: List[t]) -> List[s]: pass

@overload
def g(o: object) -> 'B': pass
@overload
def g(o: 'A', x: Any = None) -> 'B': pass

class A: pass
class B: pass

m = map(g, [A()])
b = m # type: List[B]
a = m # type: List[A] # E: Incompatible types in assignment (expression has type "List[B]", variable has type "List[A]")
[builtins fixtures/list.pyi]


-- Boolean operators
-- -----------------


[case testOrOperationInferredFromContext]
from typing import List
class A: pass
class B: pass
class C(B): pass
a: List[A]
b: List[B]
c: List[C]
if int():
    a = a or []
if int():
    a = [] or a
if int():
    b = b or [C()]
if int():
    a = a or b # E: Incompatible types in assignment (expression has type "Union[List[A], List[B]]", variable has type "List[A]")
if int():
    b = b or c # E: Incompatible types in assignment (expression has type "Union[List[B], List[C]]", variable has type "List[B]")
[builtins fixtures/list.pyi]


-- Special cases
-- -------------


[case testSomeTypeVarsInferredFromContext]
from typing import List, TypeVar
t = TypeVar('t')
s = TypeVar('s')
# Some type variables can be inferred using context, but not all of them.
a: List[A]
def f(a: s, b: t) -> List[s]: pass
class A: pass
class B: pass
if int():
    a = f(A(), B())
if int():
    a = f(B(), B()) # E: Argument 1 to "f" has incompatible type "B"; expected "A"
[builtins fixtures/list.pyi]

[case testSomeTypeVarsInferredFromContext2]
from typing import List, TypeVar
s = TypeVar('s')
t = TypeVar('t')
def f(a: s, b: t) -> List[s]: pass
class A: pass
class B: pass
# Like testSomeTypeVarsInferredFromContext, but tvars in different order.
a: List[A]
if int():
    a = f(A(), B())
if int():
    a = f(B(), B()) # E: Argument 1 to "f" has incompatible type "B"; expected "A"
[builtins fixtures/list.pyi]

[case testLambdaInListAndHigherOrderFunction]
from typing import TypeVar, Callable, List
t = TypeVar('t')
s = TypeVar('s')
def map(f: List[Callable[[t], s]], a: List[t]) -> List[s]: pass
class A: pass
map(
  [lambda x: x], [])
[builtins fixtures/list.pyi]
[out]

[case testChainedAssignmentInferenceContexts]
from typing import List
i: List[int]
s: List[str]
if int():
    i = i = []
if int():
    i = s = [] # E: Incompatible types in assignment (expression has type "List[str]", variable has type "List[int]")
[builtins fixtures/list.pyi]

[case testContextForAttributeDeclaredInInit]
from typing import List
class A:
  def __init__(self):
    self.x = [] # type: List[int]  # N: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs
a = A()
a.x = []
a.x = [1]
a.x = [''] # E: List item 0 has incompatible type "str"; expected "int"
[builtins fixtures/list.pyi]

[case testListMultiplyInContext]
from typing import List
a: List[int]
if int():
    a = [None] * 3  # E: List item 0 has incompatible type "None"; expected "int"
    a = [''] * 3  # E: List item 0 has incompatible type "str"; expected "int"
[builtins fixtures/list.pyi]

[case testUnionTypeContext]
from typing import Union, List, TypeVar
T = TypeVar('T')
def f(x: Union[List[T], str]) -> None: pass
f([1])
f('')
f(1) # E: Argument 1 to "f" has incompatible type "int"; expected "Union[List[<nothing>], str]"
[builtins fixtures/isinstancelist.pyi]

[case testIgnoringInferenceContext]
from typing import TypeVar, List
T = TypeVar('T')
def f(x: List[T]) -> T: pass
def g(y: object) -> None: pass
a = [1]
g(f(a))
[builtins fixtures/list.pyi]

[case testStar2Context]
from typing import Any, Dict, Tuple, Iterable
def f1(iterable: Iterable[Tuple[str, Any]] = ()) -> None:
    f2(**dict(iterable))
def f2(iterable: Iterable[Tuple[str, Any]], **kw: Any) -> None:
    pass
[builtins fixtures/dict.pyi]
[out]

[case testInferenceInGenericFunction]
from typing import TypeVar, List
T = TypeVar('T')
def f(a: T) -> None:
    l = []  # type: List[T]
    l.append(a)
    l.append(1) # E: Argument 1 to "append" of "list" has incompatible type "int"; expected "T"
[builtins fixtures/list.pyi]
[out]

[case testInferenceInGenericClass]
from typing import TypeVar, Generic, List
S = TypeVar('S')
T = TypeVar('T')
class A(Generic[S]):
    def f(self, a: T, b: S) -> None:
        l = []  # type: List[T]
        l.append(a)
        l.append(b) # E: Argument 1 to "append" of "list" has incompatible type "S"; expected "T"
[builtins fixtures/list.pyi]
[out]

[case testLambdaInGenericFunction]
from typing import TypeVar, Callable
T = TypeVar('T')
S = TypeVar('S')
def f(a: T, b: S) -> None:
    c = lambda x: x  # type: Callable[[T], S]
[out]
main:5: error: Incompatible types in assignment (expression has type "Callable[[T], T]", variable has type "Callable[[T], S]")
main:5: error: Incompatible return value type (got "T", expected "S")

[case testLambdaInGenericClass]
from typing import TypeVar, Callable, Generic
T = TypeVar('T')
S = TypeVar('S')
class A(Generic[T]):
    def f(self, b: S) -> None:
        c = lambda x: x  # type: Callable[[T], S]
[out]
main:6: error: Incompatible types in assignment (expression has type "Callable[[T], T]", variable has type "Callable[[T], S]")
main:6: error: Incompatible return value type (got "T", expected "S")

[case testRevealTypeContext]
from typing import TypeVar, Callable, Generic
T = TypeVar('T')
class A(Generic[T]):
    pass
reveal_type(A()) # N: Revealed type is "__main__.A[<nothing>]"
b = reveal_type(A())  # type: A[int] # N: Revealed type is "__main__.A[builtins.int]"

[case testUnionWithGenericTypeItemContext]
from typing import TypeVar, Union, List

T = TypeVar('T')

def f(x: Union[T, List[int]]) -> Union[T, List[int]]: pass
reveal_type(f(1)) # N: Revealed type is "Union[builtins.int, builtins.list[builtins.int]]"
reveal_type(f([])) # N: Revealed type is "builtins.list[builtins.int]"
reveal_type(f(None)) # N: Revealed type is "Union[None, builtins.list[builtins.int]]"
[builtins fixtures/list.pyi]

[case testUnionWithGenericTypeItemContextAndStrictOptional]
# flags: --strict-optional
from typing import TypeVar, Union, List

T = TypeVar('T')

def f(x: Union[T, List[int]]) -> Union[T, List[int]]: pass
reveal_type(f(1)) # N: Revealed type is "Union[builtins.int, builtins.list[builtins.int]]"
reveal_type(f([])) # N: Revealed type is "builtins.list[builtins.int]"
reveal_type(f(None)) # N: Revealed type is "Union[None, builtins.list[builtins.int]]"
[builtins fixtures/list.pyi]

[case testUnionWithGenericTypeItemContextInMethod]
from typing import TypeVar, Union, List, Generic

T = TypeVar('T')
S = TypeVar('S')

class C(Generic[T]):
    def f(self, x: Union[T, S]) -> Union[T, S]: pass

c = C[List[int]]()
reveal_type(c.f('')) # N: Revealed type is "Union[builtins.list[builtins.int], builtins.str]"
reveal_type(c.f([1])) # N: Revealed type is "builtins.list[builtins.int]"
reveal_type(c.f([])) # N: Revealed type is "builtins.list[builtins.int]"
reveal_type(c.f(None)) # N: Revealed type is "Union[builtins.list[builtins.int], None]"
[builtins fixtures/list.pyi]

[case testGenericMethodCalledInGenericContext]
# flags: --strict-optional
from typing import TypeVar, Generic

_KT = TypeVar('_KT')
_VT = TypeVar('_VT')
_T = TypeVar('_T')

class M(Generic[_KT, _VT]):
    def get(self, k: _KT, default: _T) -> _T: ...

def f(d: M[_KT, _VT], k: _KT) -> _VT:
    return d.get(k, None)  # E: Incompatible return value type (got "None", expected "_VT")

[case testGenericMethodCalledInGenericContext2]
from typing import TypeVar, Generic, Union

_KT = TypeVar('_KT')
_VT = TypeVar('_VT')
_T = TypeVar('_T')

class M(Generic[_KT, _VT]):
    def get(self, k: _KT, default: _T) -> Union[_VT, _T]: ...

def f(d: M[_KT, _VT], k: _KT) -> Union[_VT, None]:
    return d.get(k, None)

[case testLambdaDeferredCrash]
from typing import Callable

class C:
    def f(self) -> None:
        g: Callable[[], int] = lambda: 1 or self.x
        self.x = int()

[case testInferTypeVariableFromTwoGenericTypes1]
from typing import TypeVar, List, Sequence

T = TypeVar('T')

class C: ...
class D(C): ...

def f(x: Sequence[T], y: Sequence[T]) -> List[T]: ...

reveal_type(f([C()], [D()])) # N: Revealed type is "builtins.list[__main__.C]"
[builtins fixtures/list.pyi]

[case testInferTypeVariableFromTwoGenericTypes2]
from typing import TypeVar, List

T = TypeVar('T')

class C: ...
class D(C): ...

def f(x: List[T], y: List[T]) -> List[T]: ...

f([C()], [D()]) # E: Cannot infer type argument 1 of "f"
[builtins fixtures/list.pyi]

[case testInferTypeVariableFromTwoGenericTypes3]
from typing import Generic, TypeVar

T = TypeVar('T')
T_contra = TypeVar('T_contra', contravariant=True)

class A(Generic[T_contra]): pass
class B(A[T]): pass

class C: ...
class D(C): ...

def f(x: A[T], y: A[T]) -> B[T]: ...

c: B[C]
d: B[D]
reveal_type(f(c, d)) # N: Revealed type is "__main__.B[__main__.D]"

[case testInferTypeVariableFromTwoGenericTypes4]
from typing import Generic, TypeVar, Callable, List

T = TypeVar('T')
T_contra = TypeVar('T_contra', contravariant=True)

class A(Generic[T_contra]): pass
class B(A[T_contra]): pass

class C: ...
class D(C): ...

def f(x: Callable[[B[T]], None],
      y: Callable[[B[T]], None]) -> List[T]: ...

def gc(x: A[C]) -> None: pass  # B[C]
def gd(x: A[D]) -> None: pass  # B[C]

reveal_type(f(gc, gd)) # N: Revealed type is "builtins.list[__main__.C]"
[builtins fixtures/list.pyi]

[case testWideOuterContextSubClassBound]
from typing import TypeVar

class A: ...
class B(A): ...

T = TypeVar('T', bound=B)
def f(x: T) -> T: ...
def outer(x: A) -> None: ...

outer(f(B()))
x: A = f(B())

[case testWideOuterContextSubClassBoundGenericReturn]
from typing import TypeVar, Iterable, List

class A: ...
class B(A): ...

T = TypeVar('T', bound=B)
def f(x: T) -> List[T]: ...
def outer(x: Iterable[A]) -> None: ...

outer(f(B()))
x: Iterable[A] = f(B())
[builtins fixtures/list.pyi]

[case testWideOuterContextSubClassValues]
from typing import TypeVar

class A: ...
class B(A): ...

T = TypeVar('T', B, int)
def f(x: T) -> T: ...
def outer(x: A) -> None: ...

outer(f(B()))
x: A = f(B())

[case testWideOuterContextSubClassValuesGenericReturn]
from typing import TypeVar, Iterable, List

class A: ...
class B(A): ...

T = TypeVar('T', B, int)
def f(x: T) -> List[T]: ...
def outer(x: Iterable[A]) -> None: ...

outer(f(B()))
x: Iterable[A] = f(B())
[builtins fixtures/list.pyi]

[case testWideOuterContextSubclassBoundGeneric]
from typing import TypeVar, Generic

S = TypeVar('S')
class A(Generic[S]): ...
class B(A[S]): ...

T = TypeVar('T', bound=B[int])
def f(x: T) -> T: ...
def outer(x: A[int]) -> None: ...

y: B[int]
outer(f(y))
x: A[int] = f(y)

[case testWideOuterContextSubclassBoundGenericCovariant]
from typing import TypeVar, Generic

S_co = TypeVar('S_co', covariant=True)
class A(Generic[S_co]): ...
class B(A[S_co]): ...

T = TypeVar('T', bound=B[int])
def f(x: T) -> T: ...
def outer(x: A[int]) -> None: ...

y: B[int]
outer(f(y))
x: A[int] = f(y)

[case testWideOuterContextSubclassValuesGeneric]
from typing import TypeVar, Generic

S = TypeVar('S')
class A(Generic[S]): ...
class B(A[S]): ...

T = TypeVar('T', B[int], int)
def f(x: T) -> T: ...
def outer(x: A[int]) -> None: ...

y: B[int]
outer(f(y))
x: A[int] = f(y)

[case testWideOuterContextSubclassValuesGenericCovariant]
from typing import TypeVar, Generic

S_co = TypeVar('S_co', covariant=True)
class A(Generic[S_co]): ...
class B(A[S_co]): ...

T = TypeVar('T', B[int], int)
def f(x: T) -> T: ...
def outer(x: A[int]) -> None: ...

y: B[int]
outer(f(y))
x: A[int] = f(y)

[case testWideOuterContextUnionBound]
from typing import TypeVar, Union

class A: ...
class B: ...

T = TypeVar('T', bound=B)
def f(x: T) -> T: ...
def outer(x: Union[A, B]) -> None: ...

outer(f(B()))
x: Union[A, B] = f(B())

[case testWideOuterContextUnionBoundGenericReturn]
from typing import TypeVar, Union, Iterable, List

class A: ...
class B: ...

T = TypeVar('T', bound=B)
def f(x: T) -> List[T]: ...
def outer(x: Iterable[Union[A, B]]) -> None: ...

outer(f(B()))
x: Iterable[Union[A, B]] = f(B())
[builtins fixtures/list.pyi]

[case testWideOuterContextUnionValues]
from typing import TypeVar, Union

class A: ...
class B: ...

T = TypeVar('T', B, int)
def f(x: T) -> T: ...
def outer(x: Union[A, B]) -> None: ...

outer(f(B()))
x: Union[A, B] = f(B())

[case testWideOuterContextUnionValuesGenericReturn]
from typing import TypeVar, Union, Iterable, List

class A: ...
class B: ...

T = TypeVar('T', B, int)
def f(x: T) -> List[T]: ...
def outer(x: Iterable[Union[A, B]]) -> None: ...

outer(f(B()))
x: Iterable[Union[A, B]] = f(B())
[builtins fixtures/list.pyi]

[case testWideOuterContextOptional]
# flags: --strict-optional
from typing import Optional, Type, TypeVar

class Custom:
    pass

T = TypeVar('T', bound=Custom)

def a(x: T) -> Optional[T]: ...

def b(x: T) -> Optional[T]:
    return a(x)

[case testWideOuterContextOptionalGenericReturn]
# flags: --strict-optional
from typing import Optional, Type, TypeVar, Iterable

class Custom:
    pass

T = TypeVar('T', bound=Custom)

def a(x: T) -> Iterable[Optional[T]]: ...

def b(x: T) -> Iterable[Optional[T]]:
    return a(x)

[case testWideOuterContextOptionalMethod]
# flags: --strict-optional
from typing import Optional, Type, TypeVar

class A: pass
class B: pass

T = TypeVar('T', A, B)
class C:
    def meth_a(self) -> Optional[A]:
        return self.meth(A)

    def meth(self, cls: Type[T]) -> Optional[T]: ...

[case testWideOuterContextValuesOverlapping]
from typing import TypeVar, List

class A:
    pass
class B(A):
    pass
class C:
    pass

T = TypeVar('T', A, B, C)
def foo(xs: List[T]) -> T: ...

S = TypeVar('S', B, C)
def bar(xs: List[S]) -> S:
    foo(xs)
    return xs[0]
[builtins fixtures/list.pyi]

[case testWideOuterContextOptionalTypeVarReturn]
# flags: --strict-optional
from typing import Callable, Iterable, List, Optional, TypeVar

class C:
    x: str

T = TypeVar('T')
def f(i: Iterable[T], c: Callable[[T], str]) -> Optional[T]: ...

def g(l: List[C], x: str) -> Optional[C]:
    def pred(c: C) -> str:
        return c.x
    return f(l, pred)
[builtins fixtures/list.pyi]

[case testWideOuterContextOptionalTypeVarReturnLambda]
# flags: --strict-optional
from typing import Callable, Iterable, List, Optional, TypeVar

class C:
    x: str

T = TypeVar('T')
def f(i: Iterable[T], c: Callable[[T], str]) -> Optional[T]: ...

def g(l: List[C], x: str) -> Optional[C]:
    return f(l, lambda c: reveal_type(c).x)  # N: Revealed type is "__main__.C"
[builtins fixtures/list.pyi]

[case testWideOuterContextEmpty]
from typing import List, TypeVar

T = TypeVar('T', bound=int)
def f(x: List[T]) -> T: ...

# mypy infers List[<nothing>] here, and <nothing> is a subtype of str
y: str = f([])
[builtins fixtures/list.pyi]

[case testWideOuterContextEmptyError]
from typing import List, TypeVar

T = TypeVar('T', bound=int)
def f(x: List[T]) -> List[T]: ...

# TODO: improve error message for such cases, see #3283 and #5706
y: List[str] = f([]) \
 # E: Incompatible types in assignment (expression has type "List[<nothing>]", variable has type "List[str]") \
 # N: "List" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance \
 # N: Consider using "Sequence" instead, which is covariant
[builtins fixtures/list.pyi]

[case testWideOuterContextNoArgs]
# flags: --strict-optional
from typing import TypeVar, Optional

T = TypeVar('T', bound=int)
def f(x: Optional[T] = None) -> T: ...

y: str = f()

[case testWideOuterContextNoArgsError]
# flags: --strict-optional
from typing import TypeVar, Optional, List

T = TypeVar('T', bound=int)
def f(x: Optional[T] = None) -> List[T]: ...

y: List[str] = f()  \
      # E: Incompatible types in assignment (expression has type "List[<nothing>]", variable has type "List[str]") \
      # N: "List" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance \
      # N: Consider using "Sequence" instead, which is covariant
[builtins fixtures/list.pyi]

[case testUseCovariantGenericOuterContext]
from typing import TypeVar, Callable, Tuple

T = TypeVar('T')

def f(x: Callable[..., T]) -> T:
    return x()

x: Tuple[str, ...] = f(tuple)
[builtins fixtures/tuple.pyi]
[out]

[case testUseCovariantGenericOuterContextUserDefined]
from typing import TypeVar, Callable, Generic

T_co = TypeVar('T_co', covariant=True)
T = TypeVar('T')

class G(Generic[T_co]): ...

def f(x: Callable[..., T]) -> T:
    return x()

x: G[str] = f(G)
[out]

[case testConditionalExpressionWithEmptyListAndUnionWithAny]
from typing import Union, List, Any

def f(x: Union[List[str], Any]) -> None:
    a = x if x else []
    reveal_type(a)  # N: Revealed type is "Union[builtins.list[Union[builtins.str, Any]], builtins.list[builtins.str], Any]"
[builtins fixtures/list.pyi]

[case testConditionalExpressionWithEmptyIteableAndUnionWithAny]
from typing import Union, Iterable, Any

def f(x: Union[Iterable[str], Any]) -> None:
    a = x if x else []
    reveal_type(a)  # N: Revealed type is "Union[builtins.list[Union[builtins.str, Any]], typing.Iterable[builtins.str], Any]"
[builtins fixtures/list.pyi]

[case testInferMultipleAnyUnionCovariant]
from typing import Any, Mapping, Sequence, Union

def foo(x: Union[Mapping[Any, Any], Mapping[Any, Sequence[Any]]]) -> None:
    ...
foo({1: 2})
[builtins fixtures/dict.pyi]

[case testInferMultipleAnyUnionInvariant]
from typing import Any, Dict, Sequence, Union

def foo(x: Union[Dict[Any, Any], Dict[Any, Sequence[Any]]]) -> None:
    ...
foo({1: 2})
[builtins fixtures/dict.pyi]

[case testInferMultipleAnyUnionDifferentVariance]
from typing import Any, Dict, Mapping, Sequence, Union

def foo(x: Union[Dict[Any, Any], Mapping[Any, Sequence[Any]]]) -> None:
    ...
foo({1: 2})

def bar(x: Union[Mapping[Any, Any], Dict[Any, Sequence[Any]]]) -> None:
    ...
bar({1: 2})
[builtins fixtures/dict.pyi]

[case testOptionalTypeNarrowedByGenericCall]
# flags: --strict-optional
from typing import Dict, Optional

d: Dict[str, str] = {}

def foo(arg: Optional[str] = None) -> None:
    if arg is None:
        arg = d.get("a", "b")
    reveal_type(arg)  # N: Revealed type is "builtins.str"
[builtins fixtures/dict.pyi]

[case testOptionalTypeNarrowedByGenericCall2]
# flags: --strict-optional
from typing import Dict, Optional

d: Dict[str, str] = {}
x: Optional[str]
if x:
    reveal_type(x)  # N: Revealed type is "builtins.str"
    x = d.get(x, x)
    reveal_type(x)  # N: Revealed type is "builtins.str"
[builtins fixtures/dict.pyi]

[case testOptionalTypeNarrowedByGenericCall3]
# flags: --strict-optional
from typing import Generic, TypeVar, Union

T = TypeVar("T")
def bar(arg: Union[str, T]) -> Union[str, T]: ...

def foo(arg: Union[str, int]) -> None:
    if isinstance(arg, int):
        arg = bar("default")
    reveal_type(arg)  # N: Revealed type is "builtins.str"
[builtins fixtures/isinstance.pyi]

[case testOptionalTypeNarrowedByGenericCall4]
# flags: --strict-optional
from typing import Optional, List, Generic, TypeVar

T = TypeVar("T", covariant=True)
class C(Generic[T]): ...

x: Optional[C[int]] = None
y = x = C()
reveal_type(y)  # N: Revealed type is "__main__.C[builtins.int]"

[case testOptionalTypeNarrowedByGenericCall5]
from typing import Any, Tuple, Union

i: Union[Tuple[Any, ...], int]
b: Any
i = i if isinstance(i, int) else b
reveal_type(i)  # N: Revealed type is "Union[Any, builtins.int]"
[builtins fixtures/isinstance.pyi]