Add test, refine docs, add whatsnew, separate run_presite in pylifecycle.c

Author: ambv

Doc/using/cmdline.rst

@@ -553,9 +553,10 @@ Miscellaneous options
      container system. See also :envvar:`PYTHON_CPU_COUNT`.
      If *n* is ``default``, nothing is overridden.
    * :samp:`-X presite={package.module}` specifies a module that should be
-     imported before ``site.py`` is executed.  Python needs to be
-     :ref:`built in debug mode <debug-build>` for this option to exist.
-     See also :envvar:`PYTHON_PRESITE <PYTHON_PRESITE=package.module>`.
+     imported before ``site.py`` is executed and before the :mod:`__main__`
+     module exists.  Therefore, the imported module isn't :mod:`__main__`.
+     Python needs to be :ref:`built in debug mode <debug-build>` for this
+     option to exist.  See also :envvar:`PYTHON_PRESITE`.
 
    It also allows passing arbitrary values and retrieving them through the
    :data:`sys._xoptions` dictionary.
@@ -1099,19 +1100,22 @@ Debug-mode variables
 
    Need Python configured with the :option:`--with-trace-refs` build option.
 
-.. envvar:: PYTHONDUMPREFSFILE=FILENAME
+.. envvar:: PYTHONDUMPREFSFILE
 
    If set, Python will dump objects and reference counts still alive
-   after shutting down the interpreter into a file called *FILENAME*.
+   after shutting down the interpreter into a file under the path given
+   as the value to this environment variable.
 
    Need Python configured with the :option:`--with-trace-refs` build option.
 
    .. versionadded:: 3.11
 
-.. envvar:: PYTHON_PRESITE=package.module
+.. envvar:: PYTHON_PRESITE
 
    If this variable is set to a module, that module will be imported
-   early in the interpreter lifecycle, before ``site.py`` is executed.
+   early in the interpreter lifecycle, before ``site.py`` is executed,
+   and before the :mod:`__main__` module is created.  Therefore, the
+   imported module is not treated as :mod:`__main__`.
 
    See also the :option:`-X presite <-X>` command-line option,
    which takes precedence over this variable.

Doc/whatsnew/3.13.rst

@@ -1348,3 +1348,13 @@ removed, although there is currently no date scheduled for their removal.
 
 * Remove undocumented ``PY_TIMEOUT_MAX`` constant from the limited C API.
   (Contributed by Victor Stinner in :gh:`110014`.)
+
+
+Regression Test Changes
+=======================
+
+* Python built with :file:`configure` :option:`--with-pydebug` now
+  supports a :option:`-X presite=package.module <-X>` command-line
+  option. If used, it specifies a module that should be imported early
+  in the lifecycle of the interpreter, before ``site.py`` is executed.
+  (Contributed by Łukasz Langa in :gh:`110769`.)

Lib/test/test_embed.py

@@ -1820,6 +1820,22 @@ def test_no_memleak(self):
                 self.assertEqual(refs, 0, out)
                 self.assertEqual(blocks, 0, out)
 
+    @unittest.skipUnless(support.Py_DEBUG,
+                         '-X presite requires a Python debug build')
+    def test_presite(self):
+        cmd = [sys.executable, "-I", "-X", "presite=test.reperf", "-c", "print('cmd')"]
+        proc = subprocess.run(
+            cmd,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.STDOUT,
+            text=True,
+        )
+        self.assertEqual(proc.returncode, 0)
+        out = proc.stdout.strip()
+        self.assertIn("10 times sub", out)
+        self.assertIn("CPU seconds", out)
+        self.assertIn("cmd", out)
+
 
 class StdPrinterTests(EmbeddingTestsMixin, unittest.TestCase):
     # Test PyStdPrinter_Type which is used by _PySys_SetPreliminaryStderr():

Python/pylifecycle.c

@@ -1076,6 +1076,34 @@ pyinit_main_reconfigure(PyThreadState *tstate)
 }
 
 
+static void
+run_presite(PyThreadState *tstate)
+{
+    PyInterpreterState *interp = tstate->interp;
+    const PyConfig *config = _PyInterpreterState_GetConfig(interp);
+
+    if (config->run_presite) {
+        PyObject *presite_modname = PyUnicode_FromWideChar(
+        config->run_presite,
+        wcslen(config->run_presite)
+    );
+    if (presite_modname == NULL) {
+        fprintf(stderr, "Could not convert pre-site module name to unicode\n");
+        Py_DECREF(presite_modname);
+    }
+    else {
+        PyObject *presite = PyImport_Import(presite_modname);
+        if (presite == NULL) {
+            fprintf(stderr, "pre-site import failed:\n");
+            _PyErr_Print(tstate);
+        }
+        Py_XDECREF(presite);
+        Py_DECREF(presite_modname);
+    }
+}
+}
+
+
 static PyStatus
 init_interp_main(PyThreadState *tstate)
 {
@@ -1158,25 +1186,7 @@ init_interp_main(PyThreadState *tstate)
     }
 
 #ifdef Py_DEBUG
-    if (config->run_presite) {
-        PyObject *presite_modname = PyUnicode_FromWideChar(
-            config->run_presite,
-            wcslen(config->run_presite)
-        );
-        if (presite_modname == NULL) {
-            fprintf(stderr, "Could not convert module name to unicode\n");
-            Py_DECREF(presite_modname);
-        }
-        else {
-            PyObject *presite = PyImport_Import(presite_modname);
-            if (presite == NULL) {
-                fprintf(stderr, "pre-site import failed:\n");
-                _PyErr_Print(tstate);
-            }
-            Py_XDECREF(presite);
-            Py_DECREF(presite_modname);
-        }
-    }
+    run_presite(tstate);
 #endif
 
     status = add_main_module(interp);