[1.16 regression] Relative order of property methods changes mypy output

[gpauloski]

Bug Report

In mypy 1.16, the relative ordering of property methods (i.e., getter/setter/deleter) can produce an "Invalid property setter signature" error.

To Reproduce

mypy playground with the same example

Having an @deleter or @getter before a @setter property method produces an error:

class C:
 _value: int = 0

 @property
 def value(self) -> int:
 return self._value

 @value.deleter
 def value(self) -> None: ... # error: Invalid property setter signature [misc]

 @value.setter
 def value(self, v: int) -> None: ...

$ mypy t.py
main.py:9: error: Invalid property setter signature [misc]
Found 1 error in 1 file (checked 1 source file)

Move the @value.deleter method to after @value.setter and the error is fixed.

class C:
 _value: int = 0

 @property
 def value(self) -> int:
 return self._value

 @value.setter
 def value(self, v: int) -> None: ...

 @value.deleter
 def value(self) -> None: ...

$ mypy t.py
Success: no issues found in 1 source file

Expected Behavior

The relative ordering should not alter the output of mypy. I'm not aware of any reason why the ordering should matter and all orderings pass mypy in 1.15.

Your Environment

• Mypy version used: 1.16
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.13

[sterliakov]

Introduced in #18510, TODO added in #18774

mypy/mypy/checker.py

Lines 677 to 683 in 4fe7d9f

	self.visit_decorator(defn.items[0])
	if defn.items[0].var.is_settable_property:
	# TODO: here and elsewhere we assume setter immediately follows getter.
	assert isinstance(defn.items[1], Decorator)
	# Perform a reduced visit just to infer the actual setter type.
	self.visit_decorator_inner(defn.items[1], skip_first_item=True)
	setter_type = defn.items[1].var.type

This is a known limitation for now; cc @ilevkivskyi

[ilevkivskyi]

Yeah, I was too tired to handle that, and TBH still tired. This looks lower priority than other things (unless this causes dozens of errors for you).