This backports several PRs forgh-113993, making interned strings mortal so they can be garbage-collected when no longer needed.

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

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

  • Add internal functions toexplicitly request what kind of interning is done:

    • _PyUnicode_InternMortal
    • _PyUnicode_InternImmortal
    • _PyUnicode_InternStatic

  • Switch uses ofPyUnicode_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 theSSTATE_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 forsys.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.

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

  • Add lots of assertions

• Don't immortalize in PyUnicode_InternInPlace; keep immortalizing in other API (gh-113993: Don't immortalize in PyUnicode_InternInPlace; keep immortalizing in other API #121364)

  • Switch PyUnicode_InternInPlace to _PyUnicode_InternMortal, clarify docs

  • Document immortality in some functions that takeconst char *

  This is PyUnicode_InternFromString;
  PyDict_SetItemString, PyObject_SetAttrString;
  PyObject_DelAttrString; PyUnicode_InternFromString;
  and the PyModule_Add convenience functions.

  Always point out a non-immortalizing alternative.

  • Don't immortalize user-provided attr names in _ctypes

• Immortalize names in code objects to avoid crash (gh-121863: Immortalize names in code objects to avoid crash #121903)

• Intern latin-1 one-byte strings at startup (gh-122291: Intern latin-1 one-byte strings at startup #122303)

There are some 3.12-specific changes, mainly to allow statically allocated strings in deepfreeze. (In 3.13, deepfreeze switched to the general_Py_ID/_Py_STR.)

Co-authored-by: Eric Snowericsnowcurrently@gmail.com

📚 Documentation preview 📚:https://cpython-previews--123065.org.readthedocs.build/

Issue:#113993