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

* 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, 1 insertions, 2 deletions

diff --git a/Python/ast_opt.c b/Python/ast_opt.c
index 41e906c66e8..6d1bfafef3c 100644
--- a/Python/ast_opt.c
+++ b/Python/ast_opt.c
@@ -273,10 +273,9 @@ parse_literal(PyObject *fmt, Py_ssize_t *ppos, PyArena *arena)
     PyObject *str = PyUnicode_Substring(fmt, start, pos);
     /* str = str.replace('%%', '%') */
     if (str && has_percents) {
-        _Py_DECLARE_STR(percent, "%");
         _Py_DECLARE_STR(dbl_percent, "%%");
         Py_SETREF(str, PyUnicode_Replace(str, &_Py_STR(dbl_percent),
-                                         &_Py_STR(percent), -1));
+                                         _Py_LATIN1_CHR('%'), -1));
     }
     if (!str) {
         return NULL;