Add CPython parser benchmark C source (unused extension attempt)

Early attempt at a C extension module for benchmarking CPython's PEG
parser. Superseded by the standalone bench_cpython_parser.c program,
but kept for reference.

https://claude.ai/code/session_0116H8dSsjY7pmMiZs5WWjF3

Author: claude

Modules/_parsebench.c

@@ -0,0 +1,87 @@
+/*
+ * _parsebench: C extension module that benchmarks CPython's internal PEG parser.
+ *
+ * Calls _PyParser_ASTFromString() which produces mod_ty (C struct),
+ * WITHOUT creating Python AST objects. This measures the raw C-level
+ * parsing cost only.
+ */
+
+#define Py_BUILD_CORE
+
+#include "Python.h"
+#include "pycore_parser.h"
+#include "pycore_pyarena.h"
+
+#include <time.h>
+
+/*
+ * parse_raw(source: str) -> (time_us: int, has_error: bool)
+ *
+ * Parse source as a module, returning (elapsed_microseconds, had_error).
+ * Only measures the C-level parse (mod_ty creation), not Python AST objects.
+ */
+static PyObject *
+parsebench_parse_raw(PyObject *self, PyObject *args)
+{
+    const char *source;
+    Py_ssize_t source_len;
+
+    if (!PyArg_ParseTuple(args, "s#", &source, &source_len))
+        return NULL;
+
+    PyObject *filename = PyUnicode_FromString("<bench>");
+    if (filename == NULL)
+        return NULL;
+
+    PyCompilerFlags cf = _PyCompilerFlags_INIT;
+    cf.cf_flags = PyCF_SOURCE_IS_UTF8 | PyCF_IGNORE_COOKIE;
+
+    PyArena *arena = _PyArena_New();
+    if (arena == NULL) {
+        Py_DECREF(filename);
+        return NULL;
+    }
+
+    struct timespec start, end;
+    clock_gettime(CLOCK_MONOTONIC, &start);
+
+    mod_ty mod = _PyParser_ASTFromString(source, filename, Py_file_input,
+                                          &cf, arena);
+
+    clock_gettime(CLOCK_MONOTONIC, &end);
+
+    int has_error = (mod == NULL);
+    if (has_error) {
+        /* Clear the exception — we just want to record the error */
+        PyErr_Clear();
+    }
+
+    _PyArena_Free(arena);
+    Py_DECREF(filename);
+
+    long long elapsed_ns = (end.tv_sec - start.tv_sec) * 1000000000LL
+                         + (end.tv_nsec - start.tv_nsec);
+    long long elapsed_us = elapsed_ns / 1000;
+
+    return Py_BuildValue("(Li)", elapsed_us, has_error);
+}
+
+static PyMethodDef parsebench_methods[] = {
+    {"parse_raw", parsebench_parse_raw, METH_VARARGS,
+     "Parse source at C level (mod_ty only), return (time_us, has_error)."},
+    {NULL, NULL, 0, NULL}
+};
+
+static struct PyModuleDef parsebench_module = {
+    PyModuleDef_HEAD_INIT,
+    "_parsebench",
+    "Benchmark CPython's internal PEG parser at the C struct level.",
+    -1,
+    parsebench_methods
+};
+
+PyMODINIT_FUNC
+PyInit__parsebench(void)
+{
+    return PyModule_Create(&parsebench_module);
+}