Parser and runtime support for PEP 696

Author: JelleZijlstra

Grammar/python.gram

@@ -646,21 +646,22 @@ type_params[asdl_typeparam_seq*]: '[' t=type_param_seq  ']' {
 type_param_seq[asdl_typeparam_seq*]: a[asdl_typeparam_seq*]=','.type_param+ [','] { a }
 
 type_param[typeparam_ty] (memo):
-    | a=NAME b=[type_param_bound] { _PyAST_TypeVar(a->v.Name.id, b, EXTRA) }
+    | a=NAME b=[type_param_bound] c=[type_param_default] { _PyAST_TypeVar(a->v.Name.id, b, c, EXTRA) }
     | '*' a=NAME colon=":" e=expression {
             RAISE_SYNTAX_ERROR_STARTING_FROM(colon, e->kind == Tuple_kind
                 ? "cannot use constraints with TypeVarTuple"
                 : "cannot use bound with TypeVarTuple")
         }
-    | '*' a=NAME { _PyAST_TypeVarTuple(a->v.Name.id, EXTRA) }
+    | '*' a=NAME b=[type_param_default] { _PyAST_TypeVarTuple(a->v.Name.id, b, EXTRA) }
     | '**' a=NAME colon=":" e=expression {
             RAISE_SYNTAX_ERROR_STARTING_FROM(colon, e->kind == Tuple_kind
                 ? "cannot use constraints with ParamSpec"
                 : "cannot use bound with ParamSpec")
         }
-    | '**' a=NAME { _PyAST_ParamSpec(a->v.Name.id, EXTRA) }
+    | '**' a=NAME b=[type_param_default] { _PyAST_ParamSpec(a->v.Name.id, b, EXTRA) }
 
 type_param_bound[expr_ty]: ":" e=expression { e }
+type_param_default[expr_ty]: "=" e=expression { e }
 
 # EXPRESSIONS
 # -----------

Include/internal/pycore_ast.h

@@ -23,8 +23,9 @@
 #define INTRINSIC_TYPEVAR_WITH_BOUND 3
 #define INTRINSIC_TYPEVAR_WITH_CONSTRAINTS 4
 #define INTRINSIC_SET_FUNCTION_TYPE_PARAMS 5
+#define INTRINSIC_SET_TYPEPARAM_DEFAULT 6
 
-#define MAX_INTRINSIC_2 5
+#define MAX_INTRINSIC_2 6
 
 
 typedef PyObject *(*instrinsic_func1)(PyThreadState* tstate, PyObject *value);

Include/internal/pycore_ast_state.h

@@ -13,6 +13,7 @@ extern PyObject *_Py_make_paramspec(PyThreadState *, PyObject *);
 extern PyObject *_Py_make_typevartuple(PyThreadState *, PyObject *);
 extern PyObject *_Py_make_typealias(PyThreadState *, PyObject *);
 extern PyObject *_Py_subscript_generic(PyThreadState *, PyObject *);
+extern PyObject *_Py_set_typeparam_default(PyThreadState *, PyObject *, PyObject *);
 extern int _Py_initialize_generic(PyInterpreterState *);
 extern void _Py_clear_generic_types(PyInterpreterState *);