create NameConstant AST class for None, True, and False literals (closes #16619)

3 files changed, 15 insertions, 3 deletions

diff --git a/Parser/Python.asdl b/Parser/Python.asdl
index c24d840..0d373b0 100644
--- a/Parser/Python.asdl
+++ b/Parser/Python.asdl
@@ -1,4 +1,4 @@
--- ASDL's five builtin types are identifier, int, string, bytes, object
+-- ASDL's six builtin types are identifier, int, string, bytes, object, singleton
 
 module Python
 {
@@ -69,8 +69,8 @@ module Python
          | Num(object n) -- a number as a PyObject.
          | Str(string s) -- need to specify raw, unicode, etc?
          | Bytes(bytes s)
+         | NameConstant(singleton value)
          | Ellipsis
-         -- other literals? bools?
 
          -- the following expression can appear in assignment context
          | Attribute(expr value, identifier attr, expr_context ctx)
diff --git a/Parser/asdl.py b/Parser/asdl.py
index 08aa05b..1f98ada 100644
--- a/Parser/asdl.py
+++ b/Parser/asdl.py
@@ -222,7 +222,7 @@ class ASDLParser(spark.GenericParser, object):
         " field ::= Id ? "
         return Field(type[0], opt=True)
 
-builtin_types = ("identifier", "string", "bytes", "int", "object")
+builtin_types = ("identifier", "string", "bytes", "int", "object", "singleton")
 
 # below is a collection of classes to capture the AST of an AST :-)
 # not sure if any of the methods are useful yet, but I'm adding them
diff --git a/Parser/asdl_c.py b/Parser/asdl_c.py
index a9e6626..9557ba0 100755
--- a/Parser/asdl_c.py
+++ b/Parser/asdl_c.py
@@ -820,6 +820,7 @@ static PyObject* ast2obj_object(void *o)
     Py_INCREF((PyObject*)o);
     return (PyObject*)o;
 }
+#define ast2obj_singleton ast2obj_object
 #define ast2obj_identifier ast2obj_object
 #define ast2obj_string ast2obj_object
 #define ast2obj_bytes ast2obj_object
@@ -831,6 +832,17 @@ static PyObject* ast2obj_int(long b)
 
 /* Conversion Python -> AST */
 
+static int obj2ast_singleton(PyObject *obj, PyObject** out, PyArena* arena)
+{
+    if (obj != Py_None && obj != Py_True && obj != Py_False) {
+        PyErr_SetString(PyExc_ValueError,
+                        "AST singleton must be True, False, or None");
+        return 1;
+    }
+    *out = obj;
+    return 0;
+}
+
 static int obj2ast_object(PyObject* obj, PyObject** out, PyArena* arena)
 {
     if (obj == Py_None)