[3.13] gh-113993: Allow interned strings to be mortal, and fix related issues (GH-120520) (GH-120945)

* Add an InternalDocs file describing how interning should work and how to use it.

* Add internal functions to *explicitly* request what kind of interning is done:
  - `_PyUnicode_InternMortal`
  - `_PyUnicode_InternImmortal`
  - `_PyUnicode_InternStatic`

* Switch uses of `PyUnicode_InternInPlace` to those.

* Disallow using `_Py_SetImmortal` on strings directly.
  You should use `_PyUnicode_InternImmortal` instead:
  - Strings should be interned before immortalization, otherwise you're possibly
    interning a immortalizing copy.
  - `_Py_SetImmortal` doesn't handle the `SSTATE_INTERNED_MORTAL` to
    `SSTATE_INTERNED_IMMORTAL` update, and those flags can't be changed in
    backports, as they are now part of public API and version-specific ABI.

* Add private `_only_immortal` argument for `sys.getunicodeinternedsize`, used in refleak test machinery.

* Make sure the statically allocated string singletons are unique. This means these sets are now disjoint:
  - `_Py_ID`
  - `_Py_STR` (including the empty string)
  - one-character latin-1 singletons

  Now, when you intern a singleton, that exact singleton will be interned.

* Add a `_Py_LATIN1_CHR` macro, use it instead of `_Py_ID`/`_Py_STR` for one-character latin-1 singletons everywhere (including Clinic).

* Intern `_Py_STR` singletons at startup.

* For free-threaded builds, intern `_Py_LATIN1_CHR` singletons at startup.

* Beef up the tests. Cover internal details (marked with `@cpython_only`).

* Add lots of assertions

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/Python/import.c b/Python/import.c
index 005f769..dc7ff90 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -1967,8 +1967,6 @@ import_run_extension(PyThreadState *tstate, PyModInitFunction p0,
         if (res.kind == _Py_ext_module_kind_SINGLEPHASE) {
             /* Remember the filename as the __file__ attribute */
             if (info->filename != NULL) {
-                // XXX There's a refleak somewhere with the filename.
-                // Until we can track it down, we intern it.
                 PyObject *filename = NULL;
                 if (switched) {
                     // The original filename may be allocated by subinterpreter's
@@ -1980,7 +1978,11 @@ import_run_extension(PyThreadState *tstate, PyModInitFunction p0,
                 } else {
                     filename = Py_NewRef(info->filename);
                 }
-                PyUnicode_InternInPlace(&filename);
+                // XXX There's a refleak somewhere with the filename.
+                // Until we can track it down, we immortalize it.
+                PyInterpreterState *interp = _PyInterpreterState_GET();
+                _PyUnicode_InternImmortal(interp, &filename);
+
                 if (PyModule_AddObjectRef(mod, "__file__", filename) < 0) {
                     PyErr_Clear(); /* Not important enough to report */
                 }