(This PR is on top of the changes from#104828.)

Ideally I'd like this to go into 3.12 to fix the BC issues in#104799, but maybe it's too late.

So I understand correctly, this changes the representation of a missing list fromNULL toPyList_New(0). Correct?

I am a little concerned (just a little) about the performance implications.
Which nodes will this affect in practice?

So I understand correctly, this changes the representation of a missing list fromNULL toPyList_New(0). Correct?

No, it changes from raising a TypeError to PyList_New(0). This is easier to see in the generated code than in the code generator:

@@ -9306,10 +9404,12 @@ obj2ast_expr(struct ast_state *state, PyObject* obj, expr_ty* out, PyArena*             return 1;         }         if (tmp == NULL) {-            PyErr_SetString(PyExc_TypeError, "required field \"generators\" missing from DictComp");-            return 1;+            tmp = PyList_New(0);+            if (tmp == NULL) {+                return 1;+            }         }-        else {+        {             int res;             Py_ssize_t len;             Py_ssize_t i;

So this shouldn't affect performance for code that was already working.

Thanks@JelleZijlstra for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

GH-105213 is a backport of this pull request to the3.12 branch.