bpo-45711: Remove type and traceback from exc_info (GH-30122)

* Do not PUSH/POP traceback or type to the stack as part of exc_info

* Remove exc_traceback and exc_type from _PyErr_StackItem

* Add to what's new, because this change breaks things like Cython

Author: iritkatriel

Doc/library/dis.rst

@@ -474,13 +474,15 @@ the original TOS1.
 .. opcode:: END_ASYNC_FOR
 
    Terminates an :keyword:`async for` loop.  Handles an exception raised
-   when awaiting a next item.  If TOS is :exc:`StopAsyncIteration` pop 7
+   when awaiting a next item.  If TOS is :exc:`StopAsyncIteration` pop 3
    values from the stack and restore the exception state using the second
-   three of them.  Otherwise re-raise the exception using the three values
+   of them.  Otherwise re-raise the exception using the value
    from the stack.  An exception handler block is removed from the block stack.
 
    .. versionadded:: 3.8
 
+    .. versionchanged:: 3.11
+       Exception representation on the stack now consist of one, not three, items.
 
 .. opcode:: BEFORE_ASYNC_WITH
 
@@ -561,8 +563,10 @@ iterations of the loop.
 
 .. opcode:: POP_EXCEPT
 
-   Pops three values from the stack, which are used to restore the exception state.
+   Pops a value from the stack, which is used to restore the exception state.
 
+    .. versionchanged:: 3.11
+       Exception representation on the stack now consist of one, not three, items.
 
 .. opcode:: RERAISE
 
@@ -572,27 +576,32 @@ iterations of the loop.
 
     .. versionadded:: 3.9
 
+    .. versionchanged:: 3.11
+       Exception representation on the stack now consist of one, not three, items.
 
 .. opcode:: PUSH_EXC_INFO
 
-    Pops the three values from the stack. Pushes the current exception to the top of the stack.
-    Pushes the three values originally popped back to the stack.
+    Pops a value from the stack. Pushes the current exception to the top of the stack.
+    Pushes the value originally popped back to the stack.
     Used in exception handlers.
 
     .. versionadded:: 3.11
 
 
 .. opcode:: WITH_EXCEPT_START
 
-    Calls the function in position 8 on the stack with the top three
-    items on the stack as arguments.
+    Calls the function in position 4 on the stack with arguments (type, val, tb)
+    representing the exception at the top of the stack.
     Used to implement the call ``context_manager.__exit__(*exc_info())`` when an exception
     has occurred in a :keyword:`with` statement.
 
     .. versionadded:: 3.9
     .. versionchanged:: 3.11
        The ``__exit__`` function is in position 8 of the stack rather than 7.
 
+    .. versionchanged:: 3.11
+       The ``__exit__`` function is in position 4 of the stack rather than 7.
+       Exception representation on the stack now consist of one, not three, items.
 
 .. opcode:: POP_EXCEPT_AND_RERAISE
 
@@ -890,10 +899,9 @@ All of the following opcodes use their arguments.
    Performs exception matching for ``except*``. Applies ``split(TOS)`` on
    the exception group representing TOS1. Jumps if no match is found.
 
-   Pops one item from the stack. If a match was found, pops the 3 items representing
-   the exception and pushes the 3 items representing the non-matching part of
-   the exception group, followed by the 3 items representing the matching part.
-   In other words, in case of a match it pops 4 items and pushes 6.
+   Pops one item from the stack (the match type). If a match was found,
+   next item (the exception) and pushes the non-matching part of the
+   exception group followed by the matching part.
 
    .. versionadded:: 3.11
 
@@ -903,8 +911,8 @@ All of the following opcodes use their arguments.
    Combines the raised and reraised exceptions list from TOS, into an exception
    group to propagate from a try-except* block. Uses the original exception
    group from TOS1 to reconstruct the structure of reraised exceptions. Pops
-   two items from the stack and pushes a triplet representing the exception to
-   reraise or three ``None`` if there isn't one.
+   two items from the stack and pushes 0 (for lasti, which is unused) followed
+   by the exception to reraise or ``None`` if there isn't one.
 
    .. versionadded:: 3.11
 

Doc/whatsnew/3.11.rst

@@ -195,6 +195,11 @@ Other CPython Implementation Changes
   reflected in the re-raised exception.
   (Contributed by Irit Katriel in :issue:`45711`.)
 
+* The interpreter state's representation of handled exceptions (a.k.a exc_info, or
+  _PyErr_StackItem) now has only the ``exc_value`` field, ``exc_type`` and ``exc_traceback``
+  have been removed as their values can be derived from ``exc_value``.
+  (Contributed by Irit Katriel in :issue:`45711`.)
+
 New Modules
 ===========
 

Include/cpython/pystate.h

@@ -56,7 +56,7 @@ typedef struct _err_stackitem {
      * This ensures that the exception state is not impacted by "yields"
      * from an except handler.
      */
-    PyObject *exc_type, *exc_value, *exc_traceback;
+    PyObject *exc_value;
 
     struct _err_stackitem *previous_item;
 

Include/internal/pycore_pyerrors.h

@@ -24,16 +24,7 @@ static inline PyObject* _PyErr_Occurred(PyThreadState *tstate)
 
 static inline void _PyErr_ClearExcState(_PyErr_StackItem *exc_state)
 {
-    PyObject *t, *v, *tb;
-    t = exc_state->exc_type;
-    v = exc_state->exc_value;
-    tb = exc_state->exc_traceback;
-    exc_state->exc_type = NULL;
-    exc_state->exc_value = NULL;
-    exc_state->exc_traceback = NULL;
-    Py_XDECREF(t);
-    Py_XDECREF(v);
-    Py_XDECREF(tb);
+    Py_CLEAR(exc_state->exc_value);
 }
 
 PyAPI_FUNC(PyObject*) _PyErr_StackItemToExcInfoTuple(
@@ -114,6 +105,7 @@ PyAPI_FUNC(void) _Py_NO_RETURN _Py_FatalRefcountErrorFunc(
 
 #define _Py_FatalRefcountError(message) _Py_FatalRefcountErrorFunc(__func__, message)
 
+
 #ifdef __cplusplus
 }
 #endif

Lib/importlib/_bootstrap_external.py

@@ -371,9 +371,10 @@ def _write_atomic(path, data, mode=0o666):
 #     Python 3.11a3 3464 (bpo-45636: Merge numeric BINARY_*/INPLACE_* into
 #                         BINARY_OP)
 #     Python 3.11a3 3465 (Add COPY_FREE_VARS opcode)
-#     Python 3.11a3 3466 (bpo-45292: PEP-654 except*)
+#     Python 3.11a4 3466 (bpo-45292: PEP-654 except*)
 #     Python 3.11a4 3467 (Change CALL_xxx opcodes)
 #     Python 3.11a4 3468 (Add SEND opcode)
+#     Python 3.11a4 3469 (bpo-45711: remove type, traceback from exc_info)
 
 #
 # MAGIC must change whenever the bytecode emitted by the compiler may no
@@ -383,7 +384,7 @@ def _write_atomic(path, data, mode=0o666):
 # Whenever MAGIC_NUMBER is changed, the ranges in the magic_values array
 # in PC/launcher.c must also be updated.
 
-MAGIC_NUMBER = (3468).to_bytes(2, 'little') + b'\r\n'
+MAGIC_NUMBER = (3469).to_bytes(2, 'little') + b'\r\n'
 _RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c
 
 _PYCACHE = '__pycache__'