bpo-46219, 46221: simplify except* implementation following exc_info changes. Move helpers to exceptions.c. Do not assume that exception groups are truthy. (GH-30289)

2 files changed, 17 insertions, 141 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index 9976bde..43925e6 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -1092,7 +1092,6 @@ fail:
 
 
 static int do_raise(PyThreadState *tstate, PyObject *exc, PyObject *cause);
-static PyObject *do_reraise_star(PyObject *excs, PyObject *orig);
 static int exception_group_match(
     PyObject* exc_value, PyObject *match_type,
     PyObject **match, PyObject **rest);
@@ -2777,7 +2776,7 @@ check_eval_breaker:
             assert(PyList_Check(excs));
             PyObject *orig = POP();
 
-            PyObject *val = do_reraise_star(excs, orig);
+            PyObject *val = _PyExc_PrepReraiseStar(orig, excs);
             Py_DECREF(excs);
             Py_DECREF(orig);
 
@@ -2785,8 +2784,6 @@ check_eval_breaker:
                 goto error;
             }
 
-            PyObject *lasti_unused = Py_NewRef(_PyLong_GetZero());
-            PUSH(lasti_unused);
             PUSH(val);
             DISPATCH();
         }
@@ -6313,134 +6310,6 @@ exception_group_match(PyObject* exc_value, PyObject *match_type,
     return 0;
 }
 
-/* Logic for the final raise/reraise of a try-except* contruct
-   (too complicated for inlining).
-*/
-
-static bool
-is_same_exception_metadata(PyObject *exc1, PyObject *exc2)
-{
-    assert(PyExceptionInstance_Check(exc1));
-    assert(PyExceptionInstance_Check(exc2));
-
-    PyObject *tb1 = PyException_GetTraceback(exc1);
-    PyObject *ctx1 = PyException_GetContext(exc1);
-    PyObject *cause1 = PyException_GetCause(exc1);
-    PyObject *tb2 = PyException_GetTraceback(exc2);
-    PyObject *ctx2 = PyException_GetContext(exc2);
-    PyObject *cause2 = PyException_GetCause(exc2);
-
-    bool result = (Py_Is(tb1, tb2) &&
-                   Py_Is(ctx1, ctx2) &&
-                   Py_Is(cause1, cause2));
-
-    Py_XDECREF(tb1);
-    Py_XDECREF(ctx1);
-    Py_XDECREF(cause1);
-    Py_XDECREF(tb2);
-    Py_XDECREF(ctx2);
-    Py_XDECREF(cause2);
-    return result;
-}
-
-/*
-   excs: a list of exceptions to raise/reraise
-   orig: the original except that was caught
-
-   Calculates an exception group to raise. It contains
-   all exceptions in excs, where those that were reraised
-   have same nesting structure as in orig, and those that
-   were raised (if any) are added as siblings in a new EG.
-
-   Returns NULL and sets an exception on failure.
-*/
-static PyObject *
-do_reraise_star(PyObject *excs, PyObject *orig)
-{
-    assert(PyList_Check(excs));
-    assert(PyExceptionInstance_Check(orig));
-
-    Py_ssize_t numexcs = PyList_GET_SIZE(excs);
-
-    if (numexcs == 0) {
-        return Py_NewRef(Py_None);
-    }
-
-    if (!_PyBaseExceptionGroup_Check(orig)) {
-        /* a naked exception was caught and wrapped. Only one except* clause
-         * could have executed,so there is at most one exception to raise.
-         */
-
-        assert(numexcs == 1 || (numexcs == 2 && PyList_GET_ITEM(excs, 1) == Py_None));
-
-        PyObject *e = PyList_GET_ITEM(excs, 0);
-        assert(e != NULL);
-        return Py_NewRef(e);
-    }
-
-
-    PyObject *raised_list = PyList_New(0);
-    if (raised_list == NULL) {
-        return NULL;
-    }
-    PyObject* reraised_list = PyList_New(0);
-    if (reraised_list == NULL) {
-        Py_DECREF(raised_list);
-        return NULL;
-    }
-
-    /* Now we are holding refs to raised_list and reraised_list */
-
-    PyObject *result = NULL;
-
-    /* Split excs into raised and reraised by comparing metadata with orig */
-    for (Py_ssize_t i = 0; i < numexcs; i++) {
-        PyObject *e = PyList_GET_ITEM(excs, i);
-        assert(e != NULL);
-        if (Py_IsNone(e)) {
-            continue;
-        }
-        bool is_reraise = is_same_exception_metadata(e, orig);
-        PyObject *append_list = is_reraise ? reraised_list : raised_list;
-        if (PyList_Append(append_list, e) < 0) {
-            goto done;
-        }
-    }
-
-    PyObject *reraised_eg = _PyExc_ExceptionGroupProjection(orig, reraised_list);
-    if (reraised_eg == NULL) {
-        goto done;
-    }
-
-    if (!Py_IsNone(reraised_eg)) {
-        assert(is_same_exception_metadata(reraised_eg, orig));
-    }
-
-    Py_ssize_t num_raised = PyList_GET_SIZE(raised_list);
-    if (num_raised == 0) {
-        result = reraised_eg;
-    }
-    else if (num_raised > 0) {
-        int res = 0;
-        if (!Py_IsNone(reraised_eg)) {
-            res = PyList_Append(raised_list, reraised_eg);
-        }
-        Py_DECREF(reraised_eg);
-        if (res < 0) {
-            goto done;
-        }
-        result = _PyExc_CreateExceptionGroup("", raised_list);
-        if (result == NULL) {
-            goto done;
-        }
-    }
-
-done:
-    Py_XDECREF(raised_list);
-    Py_XDECREF(reraised_list);
-    return result;
-}
-
 /* Iterate v argcnt times and store the results on the stack (via decreasing
    sp).  Return 1 for success, 0 if error.
 
diff --git a/Python/compile.c b/Python/compile.c
index 8e90b1a..48250b5 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -1134,7 +1134,7 @@ stack_effect(int opcode, int oparg, int jump)
             return jump ? 1 : 0;
 
         case PREP_RERAISE_STAR:
-             return 0;
+             return -1;
         case RERAISE:
             return -1;
         case PUSH_EXC_INFO:
@@ -3488,12 +3488,16 @@ compiler_try_except(struct compiler *c, stmt_ty s)
    [orig, res, rest]                Ln+1:     LIST_APPEND 1  ) add unhandled exc to res (could be None)
 
    [orig, res]                                PREP_RERAISE_STAR
-   [i, exc]                                   POP_JUMP_IF_TRUE      RER
-   [i, exc]                                   POP
-   [i]                                        POP
+   [exc]                                      DUP_TOP
+   [exc, exc]                                 LOAD_CONST            None
+   [exc, exc, None]                           COMPARE_IS
+   [exc, is_none]                             POP_JUMP_IF_FALSE     RER
+   [exc]                                      POP_TOP
    []                                         JUMP_FORWARD          L0
 
-   [i, exc]                         RER:      POP_EXCEPT_AND_RERAISE
+   [exc]                            RER:      ROT_TWO
+   [exc, prev_exc_info]                       POP_EXCEPT
+   [exc]                                      RERAISE      0
 
    []                               L0:       <next statement>
 */
@@ -3657,18 +3661,21 @@ compiler_try_star_except(struct compiler *c, stmt_ty s)
     compiler_use_next_block(c, reraise_star);
     ADDOP(c, PREP_RERAISE_STAR);
     ADDOP(c, DUP_TOP);
-    ADDOP_JUMP(c, POP_JUMP_IF_TRUE, reraise);
+    ADDOP_LOAD_CONST(c, Py_None);
+    ADDOP_COMPARE(c, Is);
+    ADDOP_JUMP(c, POP_JUMP_IF_FALSE, reraise);
     NEXT_BLOCK(c);
 
-    /* Nothing to reraise - pop it */
-    ADDOP(c, POP_TOP);
+    /* Nothing to reraise */
     ADDOP(c, POP_TOP);
     ADDOP(c, POP_BLOCK);
     ADDOP(c, POP_EXCEPT);
     ADDOP_JUMP(c, JUMP_FORWARD, end);
     compiler_use_next_block(c, reraise);
     ADDOP(c, POP_BLOCK);
-    ADDOP(c, POP_EXCEPT_AND_RERAISE);
+    ADDOP(c, ROT_TWO);
+    ADDOP(c, POP_EXCEPT);
+    ADDOP_I(c, RERAISE, 0);
     compiler_use_next_block(c, cleanup);
     ADDOP(c, POP_EXCEPT_AND_RERAISE);
     compiler_use_next_block(c, orelse);