bpo-42128: Structural Pattern Matching (PEP 634) (GH-22917)

Co-authored-by: Guido van Rossum <guido@python.org>
Co-authored-by: Talin <viridia@gmail.com>
Co-authored-by: Pablo Galindo <pablogsal@gmail.com>

Parser/Python.asdl

@@ -36,6 +36,8 @@ module Python
           | With(withitem* items, stmt* body, string? type_comment)
           | AsyncWith(withitem* items, stmt* body, string? type_comment)
 
+          | Match(expr subject, match_case* cases)
+
           | Raise(expr? exc, expr? cause)
           | Try(stmt* body, excepthandler* handlers, stmt* orelse, stmt* finalbody)
           | Assert(expr test, expr? msg)
@@ -87,6 +89,10 @@ module Python
          -- can appear only in Subscript
          | Slice(expr? lower, expr? upper, expr? step)
 
+         -- only used in patterns
+         | MatchAs(expr pattern, identifier name)
+         | MatchOr(expr* patterns)
+
           -- col_offset is the byte offset in the utf8 string the parser uses
           attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)
 
@@ -121,5 +127,7 @@ module Python
 
     withitem = (expr context_expr, expr? optional_vars)
 
+    match_case = (expr pattern, expr? guard, stmt* body)
+
     type_ignore = TypeIgnore(int lineno, string tag)
 }

Parser/asdl_c.py

@@ -872,9 +872,10 @@ make_type(struct ast_state *state, const char *type, PyObject* base,
         }
         PyTuple_SET_ITEM(fnames, i, field);
     }
-    result = PyObject_CallFunction((PyObject*)&PyType_Type, "s(O){OOOOOs}",
+    result = PyObject_CallFunction((PyObject*)&PyType_Type, "s(O){OOOOOOOs}",
                     type, base,
                     state->_fields, fnames,
+                    state->__match_args__, fnames,
                     state->__module__,
                     state->ast,
                     state->__doc__, doc);
@@ -1005,6 +1006,7 @@ static int add_ast_fields(struct ast_state *state)
     empty_tuple = PyTuple_New(0);
     if (!empty_tuple ||
         PyObject_SetAttrString(state->AST_type, "_fields", empty_tuple) < 0 ||
+        PyObject_SetAttrString(state->AST_type, "__match_args__", empty_tuple) < 0 ||
         PyObject_SetAttrString(state->AST_type, "_attributes", empty_tuple) < 0) {
         Py_XDECREF(empty_tuple);
         return -1;
@@ -1405,6 +1407,7 @@ def generate_module_def(mod, f, internal_h):
     state_strings = {
         "ast",
         "_fields",
+        "__match_args__",
         "__doc__",
         "__dict__",
         "__module__",