[pylint] Include name of base class in message for `redefined-slots…

…-in-subclass` (`W0244`) (#15559)

In the following situation:

```python
class Grandparent:
  __slots__ = "a"

class Parent(Grandparent): ...

class Child(Parent):
  __slots__ = "a"
```

the message for `W0244` now specifies that `a` is overwriting a slot
from `Grandparent`.

To implement this, we introduce a helper function `iter_super_classes`
which does a breadth-first traversal of the superclasses of a given
class (as long as they are defined in the same file, due to the usual
limitations of the semantic model).

Note: Python does not allow conflicting slots definitions under multiple
inheritance. Unless I'm misunderstanding something, I believe It follows
that the subposet of superclasses of a given class that redefine a given
slot is in fact totally ordered. There is therefore a unique _nearest_
superclass whose slot is being overwritten. So, you know, in case anyone
was super worried about that... you can just chill.

This is a followup to #9640 .

crates/ruff_linter/src/rules/pylint/rules/redefined_slots_in_subclass.rs

@@ -1,6 +1,6 @@
 use std::hash::Hash;
 
-use ruff_python_semantic::{analyze::class::any_super_class, SemanticModel};
+use ruff_python_semantic::{analyze::class::iter_super_class, SemanticModel};
 use rustc_hash::FxHashSet;
 
 use ruff_diagnostics::{Diagnostic, Violation};
@@ -39,14 +39,15 @@ use crate::checkers::ast::Checker;
 /// ```
 #[derive(ViolationMetadata)]
 pub(crate) struct RedefinedSlotsInSubclass {
-    name: String,
+    base: String,
+    slot_name: String,
 }
 
 impl Violation for RedefinedSlotsInSubclass {
     #[derive_message_formats]
     fn message(&self) -> String {
-        let RedefinedSlotsInSubclass { name } = self;
-        format!("Redefined slot '{name}' in subclass")
+        let RedefinedSlotsInSubclass { base, slot_name } = self;
+        format!("Slot `{slot_name}` redefined from base class `{base}`")
     }
 }
 
@@ -68,15 +69,7 @@ pub(crate) fn redefined_slots_in_subclass(checker: &mut Checker, class_def: &ast
     let semantic = checker.semantic();
     let mut diagnostics: Vec<_> = class_slots
         .iter()
-        .filter(|&slot| contained_in_super_slots(class_def, semantic, slot))
-        .map(|slot| {
-            Diagnostic::new(
-                RedefinedSlotsInSubclass {
-                    name: slot.name.to_string(),
-                },
-                slot.range(),
-            )
-        })
+        .filter_map(|slot| check_super_slots(class_def, semantic, slot))
         .collect();
     checker.diagnostics.append(&mut diagnostics);
 }
@@ -111,19 +104,25 @@ impl Ranged for Slot<'_> {
     }
 }
 
-fn contained_in_super_slots(
+fn check_super_slots(
     class_def: &ast::StmtClassDef,
     semantic: &SemanticModel,
     slot: &Slot,
-) -> bool {
-    any_super_class(class_def, semantic, &|super_class| {
-        // This function checks every super class
-        // but we want every _strict_ super class, hence:
-        if class_def.name == super_class.name {
-            return false;
-        }
-        slots_members(&super_class.body).contains(slot)
-    })
+) -> Option<Diagnostic> {
+    iter_super_class(class_def, semantic)
+        .skip(1)
+        .find_map(&|super_class: &ast::StmtClassDef| {
+            if slots_members(&super_class.body).contains(slot) {
+                return Some(Diagnostic::new(
+                    RedefinedSlotsInSubclass {
+                        base: super_class.name.to_string(),
+                        slot_name: slot.name.to_string(),
+                    },
+                    slot.range(),
+                ));
+            }
+            None
+        })
 }
 
 fn slots_members(body: &[Stmt]) -> FxHashSet<Slot> {

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLW0244_redefined_slots_in_subclass.py.snap

@@ -1,7 +1,7 @@
 ---
 source: crates/ruff_linter/src/rules/pylint/mod.rs
 ---
-redefined_slots_in_subclass.py:6:18: PLW0244 Redefined slot 'a' in subclass
+redefined_slots_in_subclass.py:6:18: PLW0244 Slot `a` redefined from base class `Base`
   |
 5 | class Subclass(Base):
 6 |     __slots__ = ("a", "d")  # [redefined-slots-in-subclass]
@@ -10,7 +10,7 @@ redefined_slots_in_subclass.py:6:18: PLW0244 Redefined slot 'a' in subclass
 8 | class Grandparent:
   |
 
-redefined_slots_in_subclass.py:17:23: PLW0244 Redefined slot 'a' in subclass
+redefined_slots_in_subclass.py:17:23: PLW0244 Slot `a` redefined from base class `Grandparent`
    |
 16 | class Child(Parent):
 17 |     __slots__ = ("c", "a")
@@ -19,14 +19,14 @@ redefined_slots_in_subclass.py:17:23: PLW0244 Redefined slot 'a' in subclass
 19 | class AnotherBase:
    |
 
-redefined_slots_in_subclass.py:23:18: PLW0244 Redefined slot 'a' in subclass
+redefined_slots_in_subclass.py:23:18: PLW0244 Slot `a` redefined from base class `AnotherBase`
    |
 22 | class AnotherChild(AnotherBase):
 23 |     __slots__ = ["a","b","e","f"]
    |                  ^^^ PLW0244
    |
 
-redefined_slots_in_subclass.py:23:22: PLW0244 Redefined slot 'b' in subclass
+redefined_slots_in_subclass.py:23:22: PLW0244 Slot `b` redefined from base class `AnotherBase`
    |
 22 | class AnotherChild(AnotherBase):
 23 |     __slots__ = ["a","b","e","f"]

crates/ruff_python_semantic/src/analyze/class.rs

@@ -1,3 +1,5 @@
+use std::collections::VecDeque;
+
 use rustc_hash::FxHashSet;
 
 use crate::analyze::typing;
@@ -70,46 +72,62 @@ pub fn any_base_class(
     inner(class_def, semantic, func, &mut FxHashSet::default())
 }
 
-/// Return `true` if any base class matches an [`ast::StmtClassDef`] predicate.
-pub fn any_super_class(
-    class_def: &ast::StmtClassDef,
-    semantic: &SemanticModel,
-    func: &dyn Fn(&ast::StmtClassDef) -> bool,
-) -> bool {
-    fn inner(
-        class_def: &ast::StmtClassDef,
-        semantic: &SemanticModel,
-        func: &dyn Fn(&ast::StmtClassDef) -> bool,
-        seen: &mut FxHashSet<BindingId>,
-    ) -> bool {
-        // If the function itself matches the pattern, then this does too.
-        if func(class_def) {
-            return true;
-        }
+/// Returns an iterator over all base classes, beginning with the
+/// given class.
+///
+/// The traversal of the class hierarchy is breadth-first, since
+/// this graph tends to have small width but could be rather deep.
+pub fn iter_super_class<'stmt>(
+    class_def: &'stmt ast::StmtClassDef,
+    semantic: &'stmt SemanticModel,
+) -> impl Iterator<Item = &'stmt ast::StmtClassDef> {
+    struct SuperClassIterator<'stmt> {
+        semantic: &'stmt SemanticModel<'stmt>,
+        to_visit: VecDeque<&'stmt ast::StmtClassDef>,
+        seen: FxHashSet<BindingId>,
+    }
 
-        // Otherwise, check every base class.
-        class_def.bases().iter().any(|expr| {
-            // If the base class extends a class that matches the pattern, then this does too.
-            if let Some(id) = semantic.lookup_attribute(map_subscript(expr)) {
-                if seen.insert(id) {
-                    let binding = semantic.binding(id);
-                    if let Some(base_class) = binding
-                        .kind
-                        .as_class_definition()
-                        .map(|id| &semantic.scopes[*id])
-                        .and_then(|scope| scope.kind.as_class())
-                    {
-                        if inner(base_class, semantic, func, seen) {
-                            return true;
+    impl<'a> Iterator for SuperClassIterator<'a> {
+        type Item = &'a ast::StmtClassDef;
+
+        fn next(&mut self) -> Option<Self::Item> {
+            let current = self.to_visit.pop_front()?;
+
+            // Add all base classes to the to_visit list
+            for expr in current.bases() {
+                if let Some(id) = self.semantic.lookup_attribute(map_subscript(expr)) {
+                    if self.seen.insert(id) {
+                        let binding = self.semantic.binding(id);
+                        if let Some(base_class) = binding
+                            .kind
+                            .as_class_definition()
+                            .map(|id| &self.semantic.scopes[*id])
+                            .and_then(|scope| scope.kind.as_class())
+                        {
+                            self.to_visit.push_back(base_class);
                         }
                     }
                 }
             }
-            false
-        })
+            Some(current)
+        }
     }
 
-    inner(class_def, semantic, func, &mut FxHashSet::default())
+    SuperClassIterator {
+        semantic,
+        to_visit: VecDeque::from([class_def]),
+        seen: FxHashSet::default(),
+    }
+}
+
+/// Return `true` if any base class, including the given class,
+/// matches an [`ast::StmtClassDef`] predicate.
+pub fn any_super_class(
+    class_def: &ast::StmtClassDef,
+    semantic: &SemanticModel,
+    func: &dyn Fn(&ast::StmtClassDef) -> bool,
+) -> bool {
+    iter_super_class(class_def, semantic).any(func)
 }
 
 #[derive(Clone, Debug)]