doc(B024): #14455 add annotated but unassgined class variables (#14502)

# Summary

Closes #14455, migrated from astral-sh/docs#106.

Author: cmp0xff

crates/ruff_linter/src/rules/flake8_bugbear/rules/abstract_base_class.rs

@@ -11,39 +11,48 @@ use crate::checkers::ast::Checker;
 use crate::registry::Rule;
 
 /// ## What it does
-/// Checks for abstract classes without abstract methods.
+/// Checks for abstract classes without abstract methods or properties.
+/// Annotated but unassigned class variables are regarded as abstract.
 ///
 /// ## Why is this bad?
 /// Abstract base classes are used to define interfaces. If an abstract base
-/// class has no abstract methods, you may have forgotten to add an abstract
-/// method to the class or omitted an `@abstractmethod` decorator.
+/// class has no abstract methods or properties, you may have forgotten
+/// to add an abstract method or property to the class,
+/// or omitted an `@abstractmethod` decorator.
 ///
 /// If the class is _not_ meant to be used as an interface, consider removing
 /// the `ABC` base class from the class definition.
 ///
 /// ## Example
 /// ```python
 /// from abc import ABC
+/// from typing import ClassVar
 ///
 ///
 /// class Foo(ABC):
+///     class_var: ClassVar[str] = "assigned"
+///
 ///     def method(self):
 ///         bar()
 /// ```
 ///
 /// Use instead:
 /// ```python
 /// from abc import ABC, abstractmethod
+/// from typing import ClassVar
 ///
 ///
 /// class Foo(ABC):
+///     class_var: ClassVar[str]  # unassigned
+///
 ///     @abstractmethod
 ///     def method(self):
 ///         bar()
 /// ```
 ///
 /// ## References
 /// - [Python documentation: `abc`](https://docs.python.org/3/library/abc.html)
+/// - [Python documentation: `typing.ClassVar`](https://docs.python.org/3/library/typing.html#typing.ClassVar)
 #[violation]
 pub struct AbstractBaseClassWithoutAbstractMethod {
     name: String,
@@ -53,7 +62,7 @@ impl Violation for AbstractBaseClassWithoutAbstractMethod {
     #[derive_message_formats]
     fn message(&self) -> String {
         let AbstractBaseClassWithoutAbstractMethod { name } = self;
-        format!("`{name}` is an abstract base class, but it has no abstract methods")
+        format!("`{name}` is an abstract base class, but it has no abstract methods or properties")
     }
 }
 

crates/ruff_linter/src/rules/flake8_bugbear/snapshots/ruff_linter__rules__flake8_bugbear__tests__B024_B024.py.snap

@@ -2,61 +2,61 @@
 source: crates/ruff_linter/src/rules/flake8_bugbear/mod.rs
 snapshot_kind: text
 ---
-B024.py:18:7: B024 `Base_1` is an abstract base class, but it has no abstract methods
+B024.py:18:7: B024 `Base_1` is an abstract base class, but it has no abstract methods or properties
    |
 18 | class Base_1(ABC):  # error
    |       ^^^^^^ B024
 19 |     def method(self):
 20 |         foo()
    |
 
-B024.py:71:7: B024 `MetaBase_1` is an abstract base class, but it has no abstract methods
+B024.py:71:7: B024 `MetaBase_1` is an abstract base class, but it has no abstract methods or properties
    |
 71 | class MetaBase_1(metaclass=ABCMeta):  # error
    |       ^^^^^^^^^^ B024
 72 |     def method(self):
 73 |         foo()
    |
 
-B024.py:82:7: B024 `abc_Base_1` is an abstract base class, but it has no abstract methods
+B024.py:82:7: B024 `abc_Base_1` is an abstract base class, but it has no abstract methods or properties
    |
 82 | class abc_Base_1(abc.ABC):  # error
    |       ^^^^^^^^^^ B024
 83 |     def method(self):
 84 |         foo()
    |
 
-B024.py:87:7: B024 `abc_Base_2` is an abstract base class, but it has no abstract methods
+B024.py:87:7: B024 `abc_Base_2` is an abstract base class, but it has no abstract methods or properties
    |
 87 | class abc_Base_2(metaclass=abc.ABCMeta):  # error
    |       ^^^^^^^^^^ B024
 88 |     def method(self):
 89 |         foo()
    |
 
-B024.py:92:7: B024 `notabc_Base_1` is an abstract base class, but it has no abstract methods
+B024.py:92:7: B024 `notabc_Base_1` is an abstract base class, but it has no abstract methods or properties
    |
 92 | class notabc_Base_1(notabc.ABC):  # error
    |       ^^^^^^^^^^^^^ B024
 93 |     def method(self):
 94 |         foo()
    |
 
-B024.py:132:7: B024 `abc_set_class_variable_2` is an abstract base class, but it has no abstract methods
+B024.py:132:7: B024 `abc_set_class_variable_2` is an abstract base class, but it has no abstract methods or properties
     |
 132 | class abc_set_class_variable_2(ABC):  # error (not an abstract attribute)
     |       ^^^^^^^^^^^^^^^^^^^^^^^^ B024
 133 |     foo = 2
     |
 
-B024.py:136:7: B024 `abc_set_class_variable_3` is an abstract base class, but it has no abstract methods
+B024.py:136:7: B024 `abc_set_class_variable_3` is an abstract base class, but it has no abstract methods or properties
     |
 136 | class abc_set_class_variable_3(ABC):  # error (not an abstract attribute)
     |       ^^^^^^^^^^^^^^^^^^^^^^^^ B024
 137 |     foo: int = 2
     |
 
-B024.py:141:7: B024 `abc_set_class_variable_4` is an abstract base class, but it has no abstract methods
+B024.py:141:7: B024 `abc_set_class_variable_4` is an abstract base class, but it has no abstract methods or properties
     |
 140 | # this doesn't actually declare a class variable, it's just an expression
 141 | class abc_set_class_variable_4(ABC):  # error

scripts/generate_mkdocs.py

@@ -110,7 +110,7 @@ def generate_rule_metadata(rule_doc: Path) -> None:
     For example:
     ```yaml
     ---
-    description: Checks for abstract classes without abstract methods.
+    description: Checks for abstract classes without abstract methods or properties.
     tags:
     - B024
     ---