Simplify iteration idioms (#13834)

Remove unnecessary uses of `.as_ref()`, `.iter()`, `&**` and similar, mostly in situations when iterating over variables. Many of these changes are only possible following #13826, when we bumped our MSRV to 1.80: several useful implementations on `&Box<[T]>` were only stabilised in Rust 1.80. Some of these changes we could have done earlier, however.

crates/ruff_python_ast/src/node.rs

@@ -2731,7 +2731,7 @@ impl AstNode for ast::ExprCompare {
 
         visitor.visit_expr(left);
 
-        for (op, comparator) in ops.iter().zip(&**comparators) {
+        for (op, comparator) in ops.iter().zip(comparators) {
             visitor.visit_cmp_op(op);
             visitor.visit_expr(comparator);
         }

crates/ruff_python_ast/src/nodes.rs

@@ -2048,7 +2048,7 @@ impl PartialEq for ConcatenatedStringLiteral {
         // The `zip` here is safe because we have checked the length of both parts.
         self.strings
             .iter()
-            .zip(other.strings.iter())
+            .zip(&other.strings)
             .all(|(s1, s2)| s1 == s2)
     }
 }
@@ -3660,6 +3660,14 @@ impl<'a> IntoIterator for &'a Parameters {
     }
 }
 
+impl<'a> IntoIterator for &'a Box<Parameters> {
+    type IntoIter = ParametersIterator<'a>;
+    type Item = AnyParameterRef<'a>;
+    fn into_iter(self) -> Self::IntoIter {
+        (&**self).into_iter()
+    }
+}
+
 /// An alternative type of AST `arg`. This is used for each function argument that might have a default value.
 /// Used by `Arguments` original type.
 ///

crates/ruff_python_ast/src/visitor.rs

@@ -459,10 +459,10 @@ pub fn walk_expr<'a, V: Visitor<'a> + ?Sized>(visitor: &mut V, expr: &'a Expr) {
             range: _,
         }) => {
             visitor.visit_expr(left);
-            for cmp_op in &**ops {
+            for cmp_op in ops {
                 visitor.visit_cmp_op(cmp_op);
             }
-            for expr in &**comparators {
+            for expr in comparators {
                 visitor.visit_expr(expr);
             }
         }