[3.14] gh-135443: Sometimes Fall Back to __main__.__dict__ For Globals (gh-135593)

For several builtin functions, we now fall back to __main__.__dict__ for the globals
when there is no current frame and _PyInterpreterState_IsRunningMain() returns
true.  This allows those functions to be run with Interpreter.call().

The affected builtins:

* exec()
* eval()
* globals()
* locals()
* vars()
* dir()

We take a similar approach with "stateless" functions, which don't use any
global variables.

(cherry picked from commit a450a0ddec, AKA gh-135491)

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

Python/ceval.c

@@ -2732,10 +2732,9 @@ _PyEval_GetFrameLocals(void)
     return locals;
 }
 
-PyObject *
-PyEval_GetGlobals(void)
+static PyObject *
+_PyEval_GetGlobals(PyThreadState *tstate)
 {
-    PyThreadState *tstate = _PyThreadState_GET();
     _PyInterpreterFrame *current_frame = _PyThreadState_GetFrame(tstate);
     if (current_frame == NULL) {
         return NULL;
@@ -2743,6 +2742,120 @@ PyEval_GetGlobals(void)
     return current_frame->f_globals;
 }
 
+PyObject *
+PyEval_GetGlobals(void)
+{
+    PyThreadState *tstate = _PyThreadState_GET();
+    return _PyEval_GetGlobals(tstate);
+}
+
+PyObject *
+_PyEval_GetGlobalsFromRunningMain(PyThreadState *tstate)
+{
+    if (!_PyInterpreterState_IsRunningMain(tstate->interp)) {
+        return NULL;
+    }
+    PyObject *mod = _Py_GetMainModule(tstate);
+    if (_Py_CheckMainModule(mod) < 0) {
+        Py_XDECREF(mod);
+        return NULL;
+    }
+    PyObject *globals = PyModule_GetDict(mod);  // borrowed
+    Py_DECREF(mod);
+    return globals;
+}
+
+static PyObject *
+get_globals_builtins(PyObject *globals)
+{
+    PyObject *builtins = NULL;
+    if (PyDict_Check(globals)) {
+        if (PyDict_GetItemRef(globals, &_Py_ID(__builtins__), &builtins) < 0) {
+            return NULL;
+        }
+    }
+    else {
+        if (PyMapping_GetOptionalItem(
+                        globals, &_Py_ID(__builtins__), &builtins) < 0)
+        {
+            return NULL;
+        }
+    }
+    return builtins;
+}
+
+static int
+set_globals_builtins(PyObject *globals, PyObject *builtins)
+{
+    if (PyDict_Check(globals)) {
+        if (PyDict_SetItem(globals, &_Py_ID(__builtins__), builtins) < 0) {
+            return -1;
+        }
+    }
+    else {
+        if (PyObject_SetItem(globals, &_Py_ID(__builtins__), builtins) < 0) {
+            return -1;
+        }
+    }
+    return 0;
+}
+
+int
+_PyEval_EnsureBuiltins(PyThreadState *tstate, PyObject *globals,
+                       PyObject **p_builtins)
+{
+    PyObject *builtins = get_globals_builtins(globals);
+    if (builtins == NULL) {
+        if (_PyErr_Occurred(tstate)) {
+            return -1;
+        }
+        builtins = PyEval_GetBuiltins();  // borrowed
+        if (builtins == NULL) {
+            assert(_PyErr_Occurred(tstate));
+            return -1;
+        }
+        Py_INCREF(builtins);
+        if (set_globals_builtins(globals, builtins) < 0) {
+            Py_DECREF(builtins);
+            return -1;
+        }
+    }
+    if (p_builtins != NULL) {
+        *p_builtins = builtins;
+    }
+    else {
+        Py_DECREF(builtins);
+    }
+    return 0;
+}
+
+int
+_PyEval_EnsureBuiltinsWithModule(PyThreadState *tstate, PyObject *globals,
+                                 PyObject **p_builtins)
+{
+    PyObject *builtins = get_globals_builtins(globals);
+    if (builtins == NULL) {
+        if (_PyErr_Occurred(tstate)) {
+            return -1;
+        }
+        builtins = PyImport_ImportModuleLevel("builtins", NULL, NULL, NULL, 0);
+        if (builtins == NULL) {
+            return -1;
+        }
+        if (set_globals_builtins(globals, builtins) < 0) {
+            Py_DECREF(builtins);
+            return -1;
+        }
+    }
+    if (p_builtins != NULL) {
+        *p_builtins = builtins;
+    }
+    else {
+        Py_DECREF(builtins);
+    }
+    return 0;
+}
+
 PyObject*
 PyEval_GetFrameLocals(void)
 {