Argument Clinic: Add support for **kwds

This adds a scaffold of support, initially only working with
strictly positional-only arguments. The FASTCALL calling
convention is not yet supported.

Author: AA-Turner

Modules/_testclinic.c

@@ -2303,6 +2303,88 @@ depr_multi_impl(PyObject *module, PyObject *a, PyObject *b, PyObject *c,
 #undef _SAVED_PY_VERSION
 
 
+/*[clinic input]
+output pop
+[clinic start generated code]*/
+/*[clinic end generated code: output=da39a3ee5e6b4b0d input=e7c7c42daced52b0]*/
+
+
+/*[clinic input]
+output push
+destination kwarg new file '{dirname}/clinic/_testclinic_kwds.c.h'
+output everything kwarg
+output docstring_prototype suppress
+output parser_prototype suppress
+output impl_definition block
+[clinic start generated code]*/
+/*[clinic end generated code: output=da39a3ee5e6b4b0d input=02965b54b3981cc4]*/
+
+#include "clinic/_testclinic_kwds.c.h"
+
+
+/*[clinic input]
+lone_kwds
+    **kwds: dict
+[clinic start generated code]*/
+
+static PyObject *
+lone_kwds_impl(PyObject *module, PyObject *kwds)
+/*[clinic end generated code: output=572549c687a0432e input=6ef338b913ecae17]*/
+{
+    Py_RETURN_NONE;
+}
+
+
+/*[clinic input]
+kwds_with_pos_only
+    a: object
+    b: object
+    /
+    **kwds: dict
+[clinic start generated code]*/
+
+static PyObject *
+kwds_with_pos_only_impl(PyObject *module, PyObject *a, PyObject *b,
+                        PyObject *kwds)
+/*[clinic end generated code: output=573096d3a7efcce5 input=da081a5d9ae8878a]*/
+{
+    Py_RETURN_NONE;
+}
+
+
+/*[clinic input]
+kwds_with_stararg
+    *args: tuple
+    **kwds: dict
+[clinic start generated code]*/
+
+static PyObject *
+kwds_with_stararg_impl(PyObject *module, PyObject *args, PyObject *kwds)
+/*[clinic end generated code: output=d4b0064626a25208 input=1be404572d685859]*/
+{
+    Py_RETURN_NONE;
+}
+
+
+/*[clinic input]
+kwds_with_pos_only_and_stararg
+    a: object
+    b: object
+    /
+    *args: tuple
+    **kwds: dict
+[clinic start generated code]*/
+
+static PyObject *
+kwds_with_pos_only_and_stararg_impl(PyObject *module, PyObject *a,
+                                    PyObject *b, PyObject *args,
+                                    PyObject *kwds)
+/*[clinic end generated code: output=af7df7640c792246 input=2fe330c7981f0829]*/
+{
+    Py_RETURN_NONE;
+}
+
+
 /*[clinic input]
 output pop
 [clinic start generated code]*/
@@ -2399,6 +2481,12 @@ static PyMethodDef tester_methods[] = {
     DEPR_KWD_NOINLINE_METHODDEF
     DEPR_KWD_MULTI_METHODDEF
     DEPR_MULTI_METHODDEF
+
+    LONE_KWDS_METHODDEF
+    KWDS_WITH_POS_ONLY_METHODDEF
+    KWDS_WITH_STARARG_METHODDEF
+    KWDS_WITH_POS_ONLY_AND_STARARG_METHODDEF
+
     {NULL, NULL}
 };
 

Modules/clinic/_testclinic_kwds.c.h

@@ -274,7 +274,7 @@ def _render_non_self(
             data.modifications.append('/* modifications for ' + name + ' */\n' + modifications.rstrip())
 
         # keywords
-        if parameter.is_vararg():
+        if parameter.is_vararg() or parameter.is_var_keyword():
             pass
         elif parameter.is_positional_only():
             data.keywords.append('')

Tools/clinic/libclinic/converter.py

@@ -1279,3 +1279,30 @@ def parse_vararg(self, *, pos_only: int, min_pos: int, max_pos: int,
             {paramname} = {start};
             {self.length_name} = {size};
             """
+
+
+# Converters for var-keyword parameters.
+
+class VarKeywordCConverter(CConverter):
+    format_unit = ''
+
+    def parse_arg(self, argname: str, displayname: str, *, limited_capi: bool) -> str | None:
+        raise AssertionError('should never be called')
+
+    def parse_var_keyword(self) -> str:
+        raise NotImplementedError
+
+
+class var_keyword_dict_converter(VarKeywordCConverter):
+    type = 'PyObject *'
+    format_unit = ''
+    c_default = 'NULL'
+
+    def cleanup(self) -> str:
+        return f'Py_XDECREF({self.parser_name});\n'
+
+    def parse_var_keyword(self) -> str:
+        param_name = self.parser_name
+        return f"""
+            {param_name} = (kwargs != NULL) ? Py_NewRef(kwargs) : PyDict_New();
+            """

Tools/clinic/libclinic/converters.py

@@ -909,27 +909,37 @@ def parse_parameter(self, line: str) -> None:
         if len(function_args.args) > 1:
             fail(f"Function {self.function.name!r} has an "
                  f"invalid parameter declaration (comma?): {line!r}")
-        if function_args.kwarg:
-            fail(f"Function {self.function.name!r} has an "
-                 f"invalid parameter declaration (**kwargs?): {line!r}")
 
+        is_vararg = is_var_keyword = False
         if function_args.vararg:
             self.check_previous_star()
             self.check_remaining_star()
             is_vararg = True
             parameter = function_args.vararg
+        elif function_args.kwarg:
+            # If the existing parameters are all positional only or ``*args``
+            # (var-positional), then we allow ``**kwds`` (var-keyword).
+            # Currently, pos-or-keyword or keyword-only arguments are not
+            # allowed with the ``**kwds`` converter.
+            if not all(p.is_positional_only() or p.is_vararg()
+                       for p in self.function.parameters.values()):
+                fail(f"Function {self.function.name!r} has an "
+                     f"invalid parameter declaration (**kwargs?): {line!r}")
+            is_var_keyword = True
+            parameter = function_args.kwarg
         else:
-            is_vararg = False
             parameter = function_args.args[0]
 
         parameter_name = parameter.arg
         name, legacy, kwargs = self.parse_converter(parameter.annotation)
         if is_vararg:
-            name = 'varpos_' + name
+            name = f'varpos_{name}'
+        elif is_var_keyword:
+            name = f'var_keyword_{name}'
 
         value: object
         if not function_args.defaults:
-            if is_vararg:
+            if is_vararg or is_var_keyword:
                 value = NULL
             else:
                 if self.parameter_state is ParamState.OPTIONAL:
@@ -1065,6 +1075,8 @@ def bad_node(self, node: ast.AST) -> None:
         kind: inspect._ParameterKind
         if is_vararg:
             kind = inspect.Parameter.VAR_POSITIONAL
+        elif is_var_keyword:
+            kind = inspect.Parameter.VAR_KEYWORD
         elif self.keyword_only:
             kind = inspect.Parameter.KEYWORD_ONLY
         else:
@@ -1116,7 +1128,7 @@ def bad_node(self, node: ast.AST) -> None:
         key = f"{parameter_name}_as_{c_name}" if c_name else parameter_name
         self.function.parameters[key] = p
 
-        if is_vararg:
+        if is_vararg or is_var_keyword:
             self.keyword_only = True
 
     @staticmethod
@@ -1450,11 +1462,16 @@ def add_parameter(text: str) -> None:
                 if p.is_vararg():
                     p_lines.append("*")
                     added_star = True
+                if p.is_var_keyword():
+                    p_lines.append("**")
 
                 name = p.converter.signature_name or p.name
                 p_lines.append(name)
 
-                if not p.is_vararg() and p.converter.is_optional():
+                if (
+                    not (p.is_vararg() or p.is_var_keyword())
+                    and p.converter.is_optional()
+                ):
                     p_lines.append('=')
                     value = p.converter.py_default
                     if not value:
@@ -1583,8 +1600,11 @@ def check_remaining_star(self, lineno: int | None = None) -> None:
 
         for p in reversed(self.function.parameters.values()):
             if self.keyword_only:
-                if (p.kind == inspect.Parameter.KEYWORD_ONLY or
-                    p.kind == inspect.Parameter.VAR_POSITIONAL):
+                if p.kind in {
+                    inspect.Parameter.KEYWORD_ONLY,
+                    inspect.Parameter.VAR_POSITIONAL,
+                    inspect.Parameter.VAR_KEYWORD
+                }:
                     return
             elif self.deprecated_positional:
                 if p.deprecated_positional == self.deprecated_positional:

Tools/clinic/libclinic/dsl_parser.py

@@ -223,6 +223,9 @@ def is_positional_only(self) -> bool:
     def is_vararg(self) -> bool:
         return self.kind == inspect.Parameter.VAR_POSITIONAL
 
+    def is_var_keyword(self) -> bool:
+        return self.kind == inspect.Parameter.VAR_KEYWORD
+
     def is_optional(self) -> bool:
         return not self.is_vararg() and (self.default is not unspecified)