8000 Type checking of class decorators by euresti · Pull Request #4544 · python/mypy · GitHub
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Type checking of class decorators #4544

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Merged
merged 5 commits into from
Feb 9, 2018
Merged

Type checking of class decorators #4544

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a0fa761
Simple type checking of class decorators
euresti Feb 5, 2018
e40c9c7
More tests/Fix tests
euresti Feb 6, 2018
3d19a70
Cleaner tests
euresti Feb 6, 2018
c900ed7
Fully decorator support
euresti Feb 6, 2018
8318c8e
Add comments, CR
euresti Feb 7, 2018
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Fully decorator support
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@euresti
euresti committed Feb 6, 2018
commit c900ed7d4e68e7b63a905c0f2cf7e55fc7aedd6f
23 changes: 18 additions & 5 deletions mypy/checker.py
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Expand Up @@ -40,7 +40,7 @@
from mypy.sametypes import is_same_type, is_same_types
from mypy.messages import MessageBuilder, make_inferred_type_note
import mypy.checkexpr
from mypy.checkmember import map_type_from_supertype, bind_self, erase_to_bound
from mypy.checkmember import map_type_from_supertype, bind_self, erase_to_bound, type_object_type
from mypy import messages
from mypy.subtypes import (
is_subtype, is_equivalent, is_proper_subtype, is_more_precise,
Expand Down Expand Up @@ -1254,10 +1254,23 @@ def visit_class_def(self, defn: ClassDef) -> None 8000 :
# Otherwise we've already found errors; more errors are not useful
self.check_multiple_inheritance(typ)

for decorator in defn.decorators:
# Currently this only checks that the decorator itself is well typed.
# TODO: Check that applying the decorator to the class would do the right thing.
self.expr_checker.accept(decorator)
if defn.decorators:
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I would leave some kind of TODO here. One of main use cases:

dec: Callable[[Type[A]], Type[B]]

@dec
class A:
    pass

def fun(arg: B) -> None:
    pass

fun(A())  # Should be OK

is still not supported.

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Added below

sig = type_object_type(defn.info, self.named_type)
# Decorators are applied in reverse order.
for decorator in reversed(defn.decorators):
if (isinstance(decorator, CallExpr)
and isinstance(decorator.analyzed, PromoteExpr)):
8000
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This exception deserves a comment.

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Done!

continue

dec = self.expr_checker.accept(decorator)
temp = self.temp_node(sig)
fullname = None
if isinstance(decorator, RefExpr):
fullname = decorator.fullname

sig, t2 = self.expr_checker.check_call(dec, [temp],
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Better use an underscore for throw-away variable.

[nodes.ARG_POS], defn,
callable_name=fullname)

def check_protocol_variance(self, defn: ClassDef) -> None:
"""Check that protocol definition is compatible with declared
Expand Down
13 changes: 9 additions & 4 deletions test-data/unit/check-classes.test
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Expand Up @@ -4236,8 +4236,15 @@ def decorate_forward_ref() -> Callable[[Type[A]], Type[A]]:
@decorate(22, 25) # E: Too many arguments for "decorate"
@decorate_forward_ref()
@decorate(11)
class A:
pass
class A: pass

@decorate # E: Argument 1 to "decorate" has incompatible type "Type[A2]"; expected "int"
class A2: pass

[case testClassDecoratorIncorrect]
def not_a_class_decorator(x: int) -> int: ...
@not_a_class_decorator(7) # E: "int" not callable
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The error message is quite obscure. I would somehow highlight that a class decorator must be a function that accepts a type. If this is too hard, then leave a TODO about this in code.

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Left a TODO. Only thing I can figure out is collect all the errors with self.msg.copy() then modify all the messages to say what we want. Or check the count of errors before and after and add another one if it has increased.

class A3: pass

not_a_function = 17
@not_a_function() # E: "int" not callable
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Also add a test for directly applying not_a_function:

@not_a_function
class C: ...

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Done

Expand All @@ -4249,5 +4256,3 @@ class C: pass

@undefined # E: Name 'undefined' is not defined
class D: pass


0