fastparse: fix for AST subscript changes in py39

Author: hauntsaninja

mypy/fastparse.py

@@ -61,7 +61,6 @@
             Expression as ast3_Expression,
             Str,
             Bytes,
-            Index,
             Num,
             UnaryOp,
             USub,
@@ -89,7 +88,6 @@ def ast3_parse(source: Union[str, bytes], filename: str, mode: str,
             Expression as ast3_Expression,
             Str,
             Bytes,
-            Index,
             Num,
             UnaryOp,
             USub,
@@ -1200,6 +1198,7 @@ def visit_Attribute(self, n: Attribute) -> Union[MemberExpr, SuperExpr]:
 
     # Subscript(expr value, slice slice, expr_context ctx)
     def visit_Subscript(self, n: ast3.Subscript) -> IndexExpr:
+        # Note this logic does the right thing for Python 3.9's AST changes to subscription
         e = IndexExpr(self.visit(n.value), self.visit(n.slice))
         self.set_line(e, n)
         if isinstance(e.index, SliceExpr):
@@ -1230,7 +1229,7 @@ def visit_List(self, n: ast3.List) -> Union[ListExpr, TupleExpr]:
 
     # Tuple(expr* elts, expr_context ctx)
     def visit_Tuple(self, n: ast3.Tuple) -> TupleExpr:
-        e = TupleExpr([self.visit(e) for e in n.elts])
+        e = TupleExpr(self.translate_expr_list(n.elts))
         return self.set_line(e, n)
 
     # --- slice ---
@@ -1246,7 +1245,7 @@ def visit_ExtSlice(self, n: ast3.ExtSlice) -> TupleExpr:
         return TupleExpr(self.translate_expr_list(n.dims))
 
     # Index(expr value)
-    def visit_Index(self, n: Index) -> Node:
+    def visit_Index(self, n: ast3.Index) -> Node:
         return self.visit(n.value)
 
 
@@ -1504,19 +1503,25 @@ def visit_Bytes(self, n: Bytes) -> Type:
 
     # Subscript(expr value, slice slice, expr_context ctx)
     def visit_Subscript(self, n: ast3.Subscript) -> Type:
-        if not isinstance(n.slice, Index):
-            self.fail(TYPE_COMMENT_SYNTAX_ERROR, self.line, getattr(n, 'col_offset', -1))
-            return AnyType(TypeOfAny.from_error)
-
-        empty_tuple_index = False
-        if isinstance(n.slice.value, ast3.Tuple):
-            params = self.translate_expr_list(n.slice.value.elts)
-            if len(n.slice.value.elts) == 0:
-                empty_tuple_index = True
+        if sys.version_info >= (3, 9):
+            if isinstance(n.slice, ast3.Slice):
+                self.fail(TYPE_COMMENT_SYNTAX_ERROR, self.line, getattr(n, 'col_offset', -1))
+                return AnyType(TypeOfAny.from_error)
+            slice = n.slice
         else:
-            params = [self.visit(n.slice.value)]
+            if not isinstance(n.slice, ast3.Index):
+                self.fail(TYPE_COMMENT_SYNTAX_ERROR, self.line, getattr(n, 'col_offset', -1))
+                return AnyType(TypeOfAny.from_error)
+            slice = n.slice.value
 
         value = self.visit(n.value)
+        if isinstance(slice, ast3.Tuple):
+            params = self.translate_expr_list(slice.elts)
+            empty_tuple_index = len(slice.elts) == 0
+        else:
+            params = [self.visit(slice)]
+            empty_tuple_index = False
+
         if isinstance(value, UnboundType) and not value.args:
             return UnboundType(value.name, params, line=self.line, column=value.column,
                                empty_tuple_index=empty_tuple_index)