bpo-36127: Argument Clinic: inline parsing code for keyword parameters. (GH-12058)

diff --git a/Python/clinic/_warnings.c.h b/Python/clinic/_warnings.c.h
index d1e50de..67ab0e3 100644
--- a/Python/clinic/_warnings.c.h
+++ b/Python/clinic/_warnings.c.h
@@ -20,19 +20,55 @@
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"message", "category", "stacklevel", "source", NULL};
-    static _PyArg_Parser _parser = {"O|OnO:warn", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "warn", 0};
+    PyObject *argsbuf[4];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 1;
     PyObject *message;
     PyObject *category = Py_None;
     Py_ssize_t stacklevel = 1;
     PyObject *source = Py_None;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &message, &category, &stacklevel, &source)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 4, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    message = args[0];
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    if (args[1]) {
+        category = args[1];
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    if (args[2]) {
+        if (PyFloat_Check(args[2])) {
+            PyErr_SetString(PyExc_TypeError,
+                            "integer argument expected, got float" );
+            goto exit;
+        }
+        {
+            Py_ssize_t ival = -1;
+            PyObject *iobj = PyNumber_Index(args[2]);
+            if (iobj != NULL) {
+                ival = PyLong_AsSsize_t(iobj);
+                Py_DECREF(iobj);
+            }
+            if (ival == -1 && PyErr_Occurred()) {
+                goto exit;
+            }
+            stacklevel = ival;
+        }
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    source = args[3];
+skip_optional_pos:
     return_value = warnings_warn_impl(module, message, category, stacklevel, source);
 
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=a4fbe6e2d1cc2091 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=b7bb54c73b5433ec input=a9049054013a1b77]*/