Issue #28257: Improved error message when pass a non-iterable as

a var-positional argument.  Added opcode BUILD_TUPLE_UNPACK_WITH_CALL.

Include/opcode.h

@@ -125,6 +125,7 @@ extern "C" {
 #define FORMAT_VALUE            155
 #define BUILD_CONST_KEY_MAP     156
 #define BUILD_STRING            157
+#define BUILD_TUPLE_UNPACK_WITH_CALL 158
 
 /* EXCEPT_HANDLER is a special, implicit block type which is created when
    entering an except handler. It is not an opcode but we define it here

Lib/importlib/_bootstrap_external.py

@@ -238,6 +238,7 @@ _code_type = type(_write_atomic.__code__)
 #                         #27985)
 #     Python 3.6b1  3376 (simplify CALL_FUNCTIONs & BUILD_MAP_UNPACK_WITH_CALL)
 #     Python 3.6b1  3377 (set __class__ cell from type.__new__ #23722)
+#     Python 3.6b2  3378 (add BUILD_TUPLE_UNPACK_WITH_CALL #28257)
 #
 # MAGIC must change whenever the bytecode emitted by the compiler may no
 # longer be understood by older implementations of the eval loop (usually
@@ -246,7 +247,7 @@ _code_type = type(_write_atomic.__code__)
 # Whenever MAGIC_NUMBER is changed, the ranges in the magic_values array
 # in PC/launcher.c must also be updated.
 
-MAGIC_NUMBER = (3377).to_bytes(2, 'little') + b'\r\n'
+MAGIC_NUMBER = (3378).to_bytes(2, 'little') + b'\r\n'
 _RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c
 
 _PYCACHE = '__pycache__'

Lib/opcode.py

@@ -196,8 +196,6 @@ def_op('MAP_ADD', 147)
 def_op('LOAD_CLASSDEREF', 148)
 hasfree.append(148)
 
-jrel_op('SETUP_ASYNC_WITH', 154)
-
 def_op('EXTENDED_ARG', 144)
 EXTENDED_ARG = 144
 
@@ -207,8 +205,11 @@ def_op('BUILD_MAP_UNPACK_WITH_CALL', 151)
 def_op('BUILD_TUPLE_UNPACK', 152)
 def_op('BUILD_SET_UNPACK', 153)
 
+jrel_op('SETUP_ASYNC_WITH', 154)
+
 def_op('FORMAT_VALUE', 155)
 def_op('BUILD_CONST_KEY_MAP', 156)
 def_op('BUILD_STRING', 157)
+def_op('BUILD_TUPLE_UNPACK_WITH_CALL', 158)
 
 del def_op, name_op, jrel_op, jabs_op

Lib/test/test_extcall.py

@@ -233,6 +233,16 @@ What about willful misconduct?
       ...
     TypeError: h() argument after * must be an iterable, not function
 
+    >>> h(1, *h)
+    Traceback (most recent call last):
+      ...
+    TypeError: h() argument after * must be an iterable, not function
+
+    >>> h(*[1], *h)
+    Traceback (most recent call last):
+      ...
+    TypeError: h() argument after * must be an iterable, not function
+
     >>> dir(*h)
     Traceback (most recent call last):
       ...

Misc/NEWS

@@ -46,6 +46,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #28257: Improved error message when pass a non-iterable as
+  a var-positional argument.  Added opcode BUILD_TUPLE_UNPACK_WITH_CALL.
+
 - Issue #28322: Fixed possible crashes when unpickle itertools objects from
   incorrect pickle data.  Based on patch by John Leitch.
 

Python/ceval.c

@@ -2509,9 +2509,10 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag)
             DISPATCH();
         }
 
+        TARGET(BUILD_TUPLE_UNPACK_WITH_CALL)
         TARGET(BUILD_TUPLE_UNPACK)
         TARGET(BUILD_LIST_UNPACK) {
-            int convert_to_tuple = opcode == BUILD_TUPLE_UNPACK;
+            int convert_to_tuple = opcode != BUILD_LIST_UNPACK;
             Py_ssize_t i;
             PyObject *sum = PyList_New(0);
             PyObject *return_value;
@@ -2524,6 +2525,16 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag)
 
                 none_val = _PyList_Extend((PyListObject *)sum, PEEK(i));
                 if (none_val == NULL) {
+                    if (opcode == BUILD_TUPLE_UNPACK_WITH_CALL &&
+                        PyErr_ExceptionMatches(PyExc_TypeError)) {
+                        PyObject *func = PEEK(1 + oparg);
+                        PyErr_Format(PyExc_TypeError,
+                                "%.200s%.200s argument after * "
+                                "must be an iterable, not %.200s",
+                                PyEval_GetFuncName(func),
+                                PyEval_GetFuncDesc(func),
+                                PEEK(i)->ob_type->tp_name);
+                    }
                     Py_DECREF(sum);
                     goto error;
                 }

Python/compile.c

@@ -987,9 +987,9 @@ PyCompile_OpcodeStackEffect(int opcode, int oparg)
             return 1-oparg;
         case BUILD_LIST_UNPACK:
         case BUILD_TUPLE_UNPACK:
+        case BUILD_TUPLE_UNPACK_WITH_CALL:
         case BUILD_SET_UNPACK:
         case BUILD_MAP_UNPACK:
-            return 1 - oparg;
         case BUILD_MAP_UNPACK_WITH_CALL:
             return 1 - oparg;
         case BUILD_MAP:
@@ -3549,7 +3549,7 @@ compiler_call_helper(struct compiler *c,
         if (nsubargs > 1) {
             /* If we ended up with more than one stararg, we need
                to concatenate them into a single sequence. */
-            ADDOP_I(c, BUILD_TUPLE_UNPACK, nsubargs);
+            ADDOP_I(c, BUILD_TUPLE_UNPACK_WITH_CALL, nsubargs);
         }
         else if (nsubargs == 0) {
             ADDOP_I(c, BUILD_TUPLE, 0);

Python/opcode_targets.h

@@ -157,7 +157,7 @@ static void *opcode_targets[256] = {
     &&TARGET_FORMAT_VALUE,
     &&TARGET_BUILD_CONST_KEY_MAP,
     &&TARGET_BUILD_STRING,
-    &&_unknown_opcode,
+    &&TARGET_BUILD_TUPLE_UNPACK_WITH_CALL,
     &&_unknown_opcode,
     &&_unknown_opcode,
     &&_unknown_opcode,