Permit ClassVar and Final without subscript in RUF012 (#6273)

Fix #6267.

crates/ruff/resources/test/fixtures/ruff/RUF012.py

@@ -11,6 +11,8 @@ class A:
     without_annotation = []
     class_variable: ClassVar[list[int]] = []
     final_variable: Final[list[int]] = []
+    class_variable_without_subscript: ClassVar = []
+    final_variable_without_subscript: Final = []
 
 
 from dataclasses import dataclass, field

crates/ruff/src/rules/ruff/rules/helpers.rs

@@ -1,6 +1,6 @@
 use ruff_python_ast::{self as ast, Expr};
 
-use ruff_python_ast::helpers::map_callable;
+use ruff_python_ast::helpers::{map_callable, map_subscript};
 use ruff_python_semantic::{BindingKind, SemanticModel};
 
 /// Return `true` if the given [`Expr`] is a special class attribute, like `__slots__`.
@@ -28,18 +28,16 @@ pub(super) fn is_dataclass_field(func: &Expr, semantic: &SemanticModel) -> bool
 
 /// Returns `true` if the given [`Expr`] is a `typing.ClassVar` annotation.
 pub(super) fn is_class_var_annotation(annotation: &Expr, semantic: &SemanticModel) -> bool {
-    let Expr::Subscript(ast::ExprSubscript { value, .. }) = &annotation else {
-        return false;
-    };
-    semantic.match_typing_expr(value, "ClassVar")
+    // ClassVar can be used either with a subscript `ClassVar[...]` or without (the type is
+    // inferred).
+    semantic.match_typing_expr(map_subscript(annotation), "ClassVar")
 }
 
 /// Returns `true` if the given [`Expr`] is a `typing.Final` annotation.
 pub(super) fn is_final_annotation(annotation: &Expr, semantic: &SemanticModel) -> bool {
-    let Expr::Subscript(ast::ExprSubscript { value, .. }) = &annotation else {
-        return false;
-    };
-    semantic.match_typing_expr(value, "Final")
+    // Final can be used either with a subscript `Final[...]` or without (the type is
+    // inferred).
+    semantic.match_typing_expr(map_subscript(annotation), "Final")
 }
 
 /// Returns `true` if the given class is a dataclass.

crates/ruff/src/rules/ruff/snapshots/ruff__rules__ruff__tests__RUF012_RUF012.py.snap

@@ -21,14 +21,14 @@ RUF012.py:11:26: RUF012 Mutable class attributes should be annotated with `typin
 13 |     final_variable: Final[list[int]] = []
    |
 
-RUF012.py:23:26: RUF012 Mutable class attributes should be annotated with `typing.ClassVar`
+RUF012.py:25:26: RUF012 Mutable class attributes should be annotated with `typing.ClassVar`
    |
-21 |     mutable_default: list[int] = []
-22 |     immutable_annotation: Sequence[int] = []
-23 |     without_annotation = []
+23 |     mutable_default: list[int] = []
+24 |     immutable_annotation: Sequence[int] = []
+25 |     without_annotation = []
    |                          ^^ RUF012
-24 |     perfectly_fine: list[int] = field(default_factory=list)
-25 |     class_variable: ClassVar[list[int]] = []
+26 |     perfectly_fine: list[int] = field(default_factory=list)
+27 |     class_variable: ClassVar[list[int]] = []
    |