Add rule to detect unnecessary class properties (#21535)

Co-authored-by: Brent Westbrook <36778786+ntBre@users.noreply.github.com>
Co-authored-by: Amethyst Reese <amethyst@n7.gg>
Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_python_semantic/src/model.rs

@@ -3,12 +3,13 @@ use std::path::Path;
 use bitflags::bitflags;
 use rustc_hash::FxHashMap;
 
-use ruff_python_ast::helpers::from_relative_import;
+use ruff_python_ast::helpers::{from_relative_import, map_subscript};
 use ruff_python_ast::name::{QualifiedName, UnqualifiedName};
 use ruff_python_ast::{self as ast, Expr, ExprContext, PySourceType, Stmt};
 use ruff_text_size::{Ranged, TextRange, TextSize};
 
 use crate::Imported;
+use crate::analyze::visibility;
 use crate::binding::{
     Binding, BindingFlags, BindingId, BindingKind, Bindings, Exceptions, FromImport, Import,
     SubmoduleImport,
@@ -2153,6 +2154,21 @@ impl<'a> SemanticModel<'a> {
             function.range() == function_def.range()
         })
     }
+
+    /// Return `true` if the model is in a `typing.Protocol` subclass or an abstract
+    /// method.
+    pub fn in_protocol_or_abstract_method(&self) -> bool {
+        self.current_scopes().any(|scope| match scope.kind {
+            ScopeKind::Class(class_def) => class_def
+                .bases()
+                .iter()
+                .any(|base| self.match_typing_expr(map_subscript(base), "Protocol")),
+            ScopeKind::Function(function_def) => {
+                visibility::is_abstract(&function_def.decorator_list, self)
+            }
+            _ => false,
+        })
+    }
 }
 
 pub struct ShadowedBinding {