Don't trigger `eq-without-hash` when `__hash__` is explicitly set to `None` (#6739)

crates/ruff/resources/test/fixtures/pylint/eq_without_hash.py

@@ -1,10 +1,11 @@
-class Person:
+class Person:  # [eq-without-hash]
     def __init__(self):
         self.name = "monty"
 
     def __eq__(self, other):
         return isinstance(other, Person) and other.name == self.name
 
+# OK
 class Language:
     def __init__(self):
         self.name = "python"
@@ -14,3 +15,9 @@ class Language:
 
     def __hash__(self):
         return hash(self.name)
+
+class MyClass:
+    def __eq__(self, other):
+        return True
+
+    __hash__ = None

crates/ruff/src/rules/pylint/rules/eq_without_hash.rs

@@ -1,7 +1,7 @@
-use ruff_python_ast::{self as ast, Ranged, Stmt};
-
 use ruff_diagnostics::{Diagnostic, Violation};
 use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::helpers::is_const_none;
+use ruff_python_ast::{self as ast, Expr, Ranged, Stmt};
 
 use crate::checkers::ast::Checker;
 
@@ -65,13 +65,30 @@ fn has_eq_without_hash(body: &[Stmt]) -> bool {
     let mut has_hash = false;
     let mut has_eq = false;
     for statement in body {
-        let Stmt::FunctionDef(ast::StmtFunctionDef { name, .. }) = statement else {
+        match statement {
+            Stmt::Assign(ast::StmtAssign { targets, value, .. }) => {
+                let [Expr::Name(ast::ExprName { id, .. })] = targets.as_slice() else {
                     continue;
                 };
-        match name.as_str() {
+
+                // Check if `__hash__` was explicitly set to `None`, as in:
+                // ```python
+                // class Class:
+                //     def __eq__(self, other):
+                //         return True
+                //
+                //     __hash__ = None
+                // ```
+                if id == "__hash__" && is_const_none(value) {
+                    has_hash = true;
+                }
+            }
+            Stmt::FunctionDef(ast::StmtFunctionDef { name, .. }) => match name.as_str() {
                 "__hash__" => has_hash = true,
                 "__eq__" => has_eq = true,
                 _ => {}
+            },
+            _ => {}
         }
     }
     has_eq && !has_hash

crates/ruff/src/rules/pylint/snapshots/ruff__rules__pylint__tests__PLW1641_eq_without_hash.py.snap

@@ -3,7 +3,7 @@ source: crates/ruff/src/rules/pylint/mod.rs
 ---
 eq_without_hash.py:1:7: PLW1641 Object does not implement `__hash__` method
   |
-1 | class Person:
+1 | class Person:  # [eq-without-hash]
   |       ^^^^^^ PLW1641
 2 |     def __init__(self):
 3 |         self.name = "monty"