[3.8] bpo-40663: Correctly handle annotations with subscripts in ast_unparse.c (GH-20156). (GH-20191)

(cherry picked from commit 2135e10dc7)

Co-authored-by: Batuhan Taskaya <batuhanosmantaskaya@gmail.com>

Lib/test/test_future.py

@@ -265,6 +265,10 @@ class AnnotationsFutureTestCase(unittest.TestCase):
         eq("dict[str, int]")
         eq("set[str,]")
         eq("tuple[str, ...]")
+        eq("tuple[(str, *types)]")
+        eq("tuple[xx:yy, (*types,)]")
+        eq("tuple[str, int, (str, int)]")
+        eq("tuple[(*int, str, str, (str, int))]")
         eq("tuple[str, int, float, dict[str, int]]")
         eq("slice[0]")
         eq("slice[0:1]")

Misc/NEWS.d/next/Core and Builtins/2020-05-17-20-38-12.bpo-40663.u2aiZf.rst

@@ -0,0 +1,2 @@
+Correctly generate annotations where parentheses are omitted but required
+(e.g: ``Type[(str, int, *other))]``.

Python/ast_unparse.c

@@ -750,6 +750,24 @@ append_ast_ext_slice(_PyUnicodeWriter *writer, slice_ty slice)
     return 0;
 }
 
+static int
+append_ast_index_slice(_PyUnicodeWriter *writer, slice_ty slice)
+{
+    int level = PR_TUPLE;
+    expr_ty value = slice->v.Index.value;
+    if (value->kind == Tuple_kind) {
+        for (Py_ssize_t i = 0; i < asdl_seq_LEN(value->v.Tuple.elts); i++) {
+            expr_ty element = asdl_seq_GET(value->v.Tuple.elts, i);
+            if (element->kind == Starred_kind) {
+                ++level;
+                break;
+            }
+        }
+    }
+    APPEND_EXPR(value, level);
+    return 0;
+}
+
 static int
 append_ast_slice(_PyUnicodeWriter *writer, slice_ty slice)
 {
@@ -759,8 +777,7 @@ append_ast_slice(_PyUnicodeWriter *writer, slice_ty slice)
     case ExtSlice_kind:
         return append_ast_ext_slice(writer, slice);
     case Index_kind:
-        APPEND_EXPR(slice->v.Index.value, PR_TUPLE);
+        return append_ast_index_slice(writer, slice);
-        return 0;
     default:
         PyErr_SetString(PyExc_SystemError,
                         "unexpected slice kind");