[case testTraitBasic1]
from mypy_extensions import trait

class A:
    line: int
    def foo(self) -> None:
        print("foo")

@trait
class T:
    def bar(self) -> None:
        print("bar")
    def baz(self) -> object:
        return None

class C(A, T):
    def baz(self) -> int:
        return 10

def use_t(t: T) -> object:
    t.bar()
    return t.baz()

def use_c(c: C) -> int:
    use_t(c)
    c.foo()
    c.bar()
    return c.baz()

use_t(C())

# This trait is dead code but there's no reason it shouldn't compile
@trait
class ChildlessTrait:
    def __init__(self) -> None:
        pass

[file driver.py]
from native import A, T, C, use_c, use_t
c = C()
c.foo()
c.bar()
assert c.baz() == 10
assert use_c(c) == 10
assert use_t(c) == 10
[out]
bar
foo
bar
bar
foo
bar
bar

[case testTraitBasic2]
from mypy_extensions import trait

class A:
    line: int
    def foo(self) -> None:
        print("foo")

@trait
class T:
    def bar(self) -> None:
        print("bar", self.baz())
    def baz(self) -> int:
        return -1

@trait
class T2:
    line: int
    def baz(self) -> int:
        return -2

class C(A, T):
    def __init__(self) -> None:
        self.line = 1337
        self.x = 12
    def baz(self) -> int:
        return self.x

class D(C, T2):
    def __init__(self) -> None:
        self.line = 1337
        self.x = 13

@trait
class T3:
    def baz(self) -> int:
        return -2

class E(T3):
    def __init__(self) -> None:
        pass


def use_t(t: T) -> None:
    t.bar()
def use_t2(t: T2) -> int:
    t.line = t.line
    return t.line

def use_c(c: C) -> int:
    use_t(c)
    c.foo()
    c.bar()
    return c.line

def use_d(d: D) -> int:
    return d.baz()

[file driver.py]
from native import A, T, C, D, use_c, use_t, use_d, use_t2
c = C()
d = D()
c.foo()
c.bar()
print("baz", c.baz())
print("baz", d.baz())
use_c(c)
use_t(c)
use_c(d)
use_t(d)
assert use_d(d) == 13
print(d.line)
assert d.line == 1337
assert use_t2(d) == 1337
[out]
foo
bar 12
baz 12
baz 13
bar 12
foo
bar 12
bar 12
bar 13
foo
bar 13
bar 13
1337

[case testTrait3]
from mypy_extensions import trait
from typing import Generic, TypeVar

@trait
class T1: pass
@trait
class T2: pass

T = TypeVar('T')

class C(Generic[T], T1, T2):
    pass

@trait
class S1(Generic[T]):
    def foo(self) -> None: pass
    def bar(self, x: T) -> T: raise Exception

@trait
class S2(S1[T]):
    def bar(self, x: T) -> T: return x

@trait
class S3(S2[T]):
    def bar(self, x: T) -> T: return x

class D(S3[bool]):
    def bar(self, x: bool) -> bool: return x


[file driver.py]
import native

[case testTrait4]
from mypy_extensions import trait
from typing import Generic, TypeVar

T = TypeVar('T')


@trait
class S1(Generic[T]):
    def bar(self) -> T: raise Exception

class S2(S1[bool]):
    def bar(self) -> bool: return False

class D(S2):
    pass

def lol(x: S1) -> None:
    x.bar()

[file driver.py]
import native
native.lol(native.D())

[case testTraitOrdering]
import other_b
# Regression test for a bug where inheriting from a class that
# inherited from a trait that got processed later on the command line
# filed to compile.
[file other_b.py]
from other_c import Plugin

class Whatever(Plugin):
    pass

[file other_c.py]
from mypy_extensions import trait

@trait
class Base:
    x = None  # type: int

class Plugin(Base):
    def __init__(self) -> None:
        self.x = 10

[file driver.py]
from native import *

[case testDiamond]
from mypy_extensions import trait

@trait
class Base:
    def get_value(self) -> str:
        return "Base"

@trait
class Trait(Base):
    def get_value(self) -> str:
        return "Trait"

class Message(Base):
    def show_message(self) -> None:
        print("I am a " + self.get_value())

class DerivedMessage(Message, Trait):
    pass

[file driver.py]
from native import *
a = Message()
a.show_message()
b = DerivedMessage()
b.show_message()

[out]
I am a Base
I am a Trait

[case testTraitAttrsSubTrait]
from mypy_extensions import trait

class A:
    a: int

@trait
class T1:
    x: int

@trait
class T2(T1):
    y: int

class C(A, T2):
    c: int

def f(t1: T1, t2: T2) -> None:
    t1.x, t2.x = t2.x, t1.x

def g(t1: T1, t2: T2) -> None:
    t2.y = t1.x

def get_x(c: C) -> int:
    return c.x

def get_y(c: C) -> int:
    return c.y

[file driver.py]
from native import C, f, g, get_x, get_y

c1 = C()
c2 = C()

c1.x = 1
c1.y = 0
c2.x = 2
c2.y = 0

f(c1, c2)
assert c1.x == 2
assert c2.x == 1
assert get_x(c1) == 2
assert get_x(c2) == 1

assert get_y(c2) == 0
g(c1, c2)
assert get_y(c2) == 2
[out]

[case testTraitAttrsTriangle]
from mypy_extensions import trait

class A:
    a: int

@trait
class T(A):
    x: int
    def meth(self) -> int:
        return self.a

class B(A):
    b: int

class C(B, T):
    pass

def take_t(t: T) -> int:
    return t.x + t.meth()

def take_c(c: C) -> int:
    return c.x + c.meth()

[file driver.py]
from native import C, take_t, take_c

c = C()
c.a = 1
c.x = 10

assert take_t(c) == take_c(c) == 11
[out]

[case testTraitAttrsTree]
from mypy_extensions import trait

class A:
    a: int

@trait
class T1:
    x: int

class B(A, T1):
    b: int

@trait
class T2:
    x: int

class C(B, T2):
    pass

def f(t1: T1, t2: T2) -> None:
    t1.x, t2.x = t2.x, t1.x

def g(c1: C, c2: C) -> None:
    c1.x, c2.x = c2.x, c1.x

[file driver.py]
from native import C, f, g

c1 = C()
c2 = C()

c1.x = 1
c2.x = 2

f(c1, c2)
assert c1.x == 2
assert c2.x == 1

g(c1, c2)
assert c1.x == 1
assert c2.x == 2
[out]

[case testTraitErrorMessages]
from mypy_extensions import trait

@trait
class Trait:
    pass

def create() -> Trait:
    return Trait()

[file driver.py]
from native import Trait, create
from testutil import assertRaises

with assertRaises(TypeError, "traits may not be directly created"):
    Trait()

with assertRaises(TypeError, "traits may not be directly created"):
    create()

class Sub(Trait):
    pass

with assertRaises(TypeError, "interpreted classes cannot inherit from compiled traits"):
    Sub()