gh-76785: Drop PyInterpreterID_Type (gh-117101)

I added it quite a while ago as a strategy for managing interpreter lifetimes relative to the PEP 554 (now 734) implementation.  Relatively recently I refactored that implementation to no longer rely on InterpreterID objects.  Thus now I'm removing it.

Modules/_interpreters_common.h

@@ -19,3 +19,20 @@ clear_xid_class(PyTypeObject *cls)
     return _PyCrossInterpreterData_UnregisterClass(cls);
 }
 #endif
+
+
+#ifdef RETURNS_INTERPID_OBJECT
+static PyObject *
+get_interpid_obj(PyInterpreterState *interp)
+{
+    if (_PyInterpreterState_IDInitref(interp) != 0) {
+        return NULL;
+    };
+    int64_t id = PyInterpreterState_GetID(interp);
+    if (id < 0) {
+        return NULL;
+    }
+    assert(id < LLONG_MAX);
+    return PyLong_FromLongLong(id);
+}
+#endif

Modules/_testcapimodule.c

@@ -13,7 +13,6 @@
 #include "_testcapi/parts.h"
 
 #include "frameobject.h"          // PyFrame_New()
-#include "interpreteridobject.h"  // PyInterpreterID_Type
 #include "marshal.h"              // PyMarshal_WriteLongToFile()
 
 #include <float.h>                // FLT_MAX
@@ -1449,12 +1448,6 @@ run_in_subinterp(PyObject *self, PyObject *args)
     return PyLong_FromLong(r);
 }
 
-static PyObject *
-get_interpreterid_type(PyObject *self, PyObject *Py_UNUSED(ignored))
-{
-    return Py_NewRef(&PyInterpreterID_Type);
-}
-
 static PyMethodDef ml;
 
 static PyObject *
@@ -3299,7 +3292,6 @@ static PyMethodDef TestMethods[] = {
     {"crash_no_current_thread", crash_no_current_thread,         METH_NOARGS},
     {"test_current_tstate_matches", test_current_tstate_matches, METH_NOARGS},
     {"run_in_subinterp",        run_in_subinterp,                METH_VARARGS},
-    {"get_interpreterid_type",  get_interpreterid_type,          METH_NOARGS},
     {"create_cfunction",        create_cfunction,                METH_NOARGS},
     {"call_in_temporary_c_thread", call_in_temporary_c_thread, METH_VARARGS,
      PyDoc_STR("set_error_class(error_class) -> None")},

Modules/_testinternalcapi.c

@@ -1475,6 +1475,83 @@ run_in_subinterp_with_config(PyObject *self, PyObject *args, PyObject *kwargs)
 }
 
 
+static PyObject *
+normalize_interp_id(PyObject *self, PyObject *idobj)
+{
+    int64_t interpid = _PyInterpreterState_ObjectToID(idobj);
+    if (interpid < 0) {
+        return NULL;
+    }
+    return PyLong_FromLongLong(interpid);
+}
+
+static PyObject *
+unused_interpreter_id(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    int64_t interpid = INT64_MAX;
+    assert(interpid > _PyRuntime.interpreters.next_id);
+    return PyLong_FromLongLong(interpid);
+}
+
+static PyObject *
+new_interpreter(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    // Unlike _interpreters.create(), we do not automatically link
+    // the interpreter to its refcount.
+    PyThreadState *save_tstate = PyThreadState_Get();
+    const PyInterpreterConfig config = \
+            (PyInterpreterConfig)_PyInterpreterConfig_INIT;
+    PyThreadState *tstate = NULL;
+    PyStatus status = Py_NewInterpreterFromConfig(&tstate, &config);
+    PyThreadState_Swap(save_tstate);
+    if (PyStatus_Exception(status)) {
+        _PyErr_SetFromPyStatus(status);
+        return NULL;
+    }
+    PyInterpreterState *interp = PyThreadState_GetInterpreter(tstate);
+
+    if (_PyInterpreterState_IDInitref(interp) < 0) {
+        goto error;
+    }
+
+    int64_t interpid = PyInterpreterState_GetID(interp);
+    if (interpid < 0) {
+        goto error;
+    }
+    PyObject *idobj = PyLong_FromLongLong(interpid);
+    if (idobj == NULL) {
+        goto error;
+    }
+
+    PyThreadState_Swap(tstate);
+    PyThreadState_Clear(tstate);
+    PyThreadState_Swap(save_tstate);
+    PyThreadState_Delete(tstate);
+
+    return idobj;
+
+error:
+    save_tstate = PyThreadState_Swap(tstate);
+    Py_EndInterpreter(tstate);
+    PyThreadState_Swap(save_tstate);
+    return NULL;
+}
+
+static PyObject *
+interpreter_exists(PyObject *self, PyObject *idobj)
+{
+    PyInterpreterState *interp = _PyInterpreterState_LookUpIDObject(idobj);
+    if (interp == NULL) {
+        if (PyErr_ExceptionMatches(PyExc_InterpreterNotFoundError)) {
+            PyErr_Clear();
+            Py_RETURN_FALSE;
+        }
+        assert(PyErr_Occurred());
+        return NULL;
+    }
+    Py_RETURN_TRUE;
+}
+
 static PyObject *
 get_interpreter_refcount(PyObject *self, PyObject *idobj)
 {
@@ -1509,6 +1586,41 @@ unlink_interpreter_refcount(PyObject *self, PyObject *idobj)
     Py_RETURN_NONE;
 }
 
+static PyObject *
+interpreter_refcount_linked(PyObject *self, PyObject *idobj)
+{
+    PyInterpreterState *interp = _PyInterpreterState_LookUpIDObject(idobj);
+    if (interp == NULL) {
+        return NULL;
+    }
+    if (_PyInterpreterState_RequiresIDRef(interp)) {
+        Py_RETURN_TRUE;
+    }
+    Py_RETURN_FALSE;
+}
+
+static PyObject *
+interpreter_incref(PyObject *self, PyObject *idobj)
+{
+    PyInterpreterState *interp = _PyInterpreterState_LookUpIDObject(idobj);
+    if (interp == NULL) {
+        return NULL;
+    }
+    _PyInterpreterState_IDIncref(interp);
+    Py_RETURN_NONE;
+}
+
+static PyObject *
+interpreter_decref(PyObject *self, PyObject *idobj)
+{
+    PyInterpreterState *interp = _PyInterpreterState_LookUpIDObject(idobj);
+    if (interp == NULL) {
+        return NULL;
+    }
+    _PyInterpreterState_IDDecref(interp);
+    Py_RETURN_NONE;
+}
+
 
 static void
 _xid_capsule_destructor(PyObject *capsule)
@@ -1749,9 +1861,16 @@ static PyMethodDef module_functions[] = {
     {"run_in_subinterp_with_config",
      _PyCFunction_CAST(run_in_subinterp_with_config),
      METH_VARARGS | METH_KEYWORDS},
+    {"normalize_interp_id", normalize_interp_id, METH_O},
+    {"unused_interpreter_id", unused_interpreter_id, METH_NOARGS},
+    {"new_interpreter", new_interpreter, METH_NOARGS},
+    {"interpreter_exists", interpreter_exists, METH_O},
     {"get_interpreter_refcount", get_interpreter_refcount, METH_O},
     {"link_interpreter_refcount", link_interpreter_refcount,     METH_O},
     {"unlink_interpreter_refcount", unlink_interpreter_refcount, METH_O},
+    {"interpreter_refcount_linked", interpreter_refcount_linked, METH_O},
+    {"interpreter_incref", interpreter_incref, METH_O},
+    {"interpreter_decref", interpreter_decref, METH_O},
     {"compile_perf_trampoline_entry", compile_perf_trampoline_entry, METH_VARARGS},
     {"perf_trampoline_set_persist_after_fork", perf_trampoline_set_persist_after_fork, METH_VARARGS},
     {"get_crossinterp_data",    get_crossinterp_data,            METH_VARARGS},

Modules/_xxinterpchannelsmodule.c

@@ -6,7 +6,6 @@
 #endif
 
 #include "Python.h"
-#include "interpreteridobject.h"
 #include "pycore_crossinterp.h"   // struct _xid
 #include "pycore_interp.h"        // _PyInterpreterState_LookUpID()
 
@@ -18,7 +17,9 @@
 #endif
 
 #define REGISTERS_HEAP_TYPES
+#define RETURNS_INTERPID_OBJECT
 #include "_interpreters_common.h"
+#undef RETURNS_INTERPID_OBJECT
 #undef REGISTERS_HEAP_TYPES
 
 
@@ -2908,7 +2909,7 @@ channelsmod_list_interpreters(PyObject *self, PyObject *args, PyObject *kwds)
             goto except;
         }
         if (res) {
-            interpid_obj = PyInterpreterState_GetIDObject(interp);
+            interpid_obj = get_interpid_obj(interp);
             if (interpid_obj == NULL) {
                 goto except;
             }

Modules/_xxsubinterpretersmodule.c

@@ -16,10 +16,11 @@
 #include "pycore_pyerrors.h"      // _Py_excinfo
 #include "pycore_pystate.h"       // _PyInterpreterState_SetRunningMain()
 
-#include "interpreteridobject.h"
 #include "marshal.h"              // PyMarshal_ReadObjectFromString()
 
+#define RETURNS_INTERPID_OBJECT
 #include "_interpreters_common.h"
+#undef RETURNS_INTERPID_OBJECT
 
 
 #define MODULE_NAME _xxsubinterpreters
@@ -38,20 +39,6 @@ _get_current_interp(void)
 #define look_up_interp _PyInterpreterState_LookUpIDObject
 
 
-static PyObject *
-get_interpid_obj(PyInterpreterState *interp)
-{
-    if (_PyInterpreterState_IDInitref(interp) != 0) {
-        return NULL;
-    };
-    int64_t id = PyInterpreterState_GetID(interp);
-    if (id < 0) {
-        return NULL;
-    }
-    assert(id < LLONG_MAX);
-    return PyLong_FromLongLong(id);
-}
-
 static PyObject *
 _get_current_module(void)
 {