Allow starred expressions in subscripts

Author: charliermarsh

compiler/parser/python.lalrpop

@@ -1037,7 +1037,7 @@ SubscriptList: ast::Expr = {
 };
 
 Subscript: ast::Expr = {
-    NamedExpressionTest,
+    TestOrStarNamedExpr,
     <location:@L> <e1:Test<"all">?> ":" <e2:Test<"all">?> <e3:SliceOp?> <end_location:@R> => {
         let lower = e1.map(Box::new);
         let upper = e2.map(Box::new);

compiler/parser/src/parser.rs

@@ -392,6 +392,18 @@ with (0 as a, 1 as b,): pass
         }
     }
 
+    #[test]
+    fn test_star_index() {
+        let source = "\
+array_slice = array[0, *idxs, -1]
+array[0, *idxs, -1] = array_slice
+array[*idxs_to_select, *idxs_to_select]
+array[3:5, *idxs_to_select]
+";
+        let parse_ast = parse_program(source, "<test>").unwrap();
+        insta::assert_debug_snapshot!(parse_ast);
+    }
+
     #[test]
     fn test_generator_expression_argument() {
         let source = r#"' '.join(