GH-132554: "Virtual" iterators

Include/internal/pycore_ceval.h

@@ -353,6 +353,8 @@ PyAPI_FUNC(_PyStackRef) _PyFloat_FromDouble_ConsumeInputs(_PyStackRef left, _PyS
 extern int _PyRunRemoteDebugger(PyThreadState *tstate);
 #endif
 
+_PyStackRef _PyForIter_NextWithIndex(PyObject *seq, _PyStackRef index);
+
 #ifdef __cplusplus
 }
 #endif

Include/internal/pycore_code.h

@@ -313,7 +313,7 @@ extern void _Py_Specialize_CompareOp(_PyStackRef lhs, _PyStackRef rhs,
                                      _Py_CODEUNIT *instr, int oparg);
 extern void _Py_Specialize_UnpackSequence(_PyStackRef seq, _Py_CODEUNIT *instr,
                                           int oparg);
-extern void _Py_Specialize_ForIter(_PyStackRef iter, _Py_CODEUNIT *instr, int oparg);
+extern void _Py_Specialize_ForIter(_PyStackRef iter, _PyStackRef null_or_index, _Py_CODEUNIT *instr, int oparg);
 extern void _Py_Specialize_Send(_PyStackRef receiver, _Py_CODEUNIT *instr);
 extern void _Py_Specialize_ToBool(_PyStackRef value, _Py_CODEUNIT *instr);
 extern void _Py_Specialize_ContainsOp(_PyStackRef value, _Py_CODEUNIT *instr);

Include/internal/pycore_compile.h

@@ -95,6 +95,7 @@ typedef enum {
 enum _PyCompile_FBlockType {
      COMPILE_FBLOCK_WHILE_LOOP,
      COMPILE_FBLOCK_FOR_LOOP,
+     COMPILE_FBLOCK_ASYNC_FOR_LOOP,
      COMPILE_FBLOCK_TRY_EXCEPT,
      COMPILE_FBLOCK_FINALLY_TRY,
      COMPILE_FBLOCK_FINALLY_END,

Include/internal/pycore_magic_number.h

@@ -276,6 +276,8 @@ Known values:
     Python 3.14a7 3621 (Optimize LOAD_FAST opcodes into LOAD_FAST_BORROW)
     Python 3.14a7 3622 (Store annotations in different class dict keys)
     Python 3.14a7 3623 (Add BUILD_INTERPOLATION & BUILD_TEMPLATE opcodes)
+    Python 3.14a7 3624 (Virtual iterators)
+
 
     Python 3.15 will start with 3650
 
@@ -288,7 +290,7 @@ PC/launcher.c must also be updated.
 
 */
 
-#define PYC_MAGIC_NUMBER 3623
+#define PYC_MAGIC_NUMBER 3624
 /* This is equivalent to converting PYC_MAGIC_NUMBER to 2 bytes
    (little-endian) and then appending b'\r\n'. */
 #define PYC_MAGIC_NUMBER_TOKEN \

Include/internal/pycore_stackref.h

@@ -233,6 +233,9 @@ extern intptr_t PyStackRef_UntagInt(_PyStackRef ref);
 
 extern _PyStackRef PyStackRef_TagInt(intptr_t i);
 
+/* Increments a tagged int, but does not check for overflow */
+extern _PyStackRef PyStackRef_IncrementTaggedIntNoOverflow(_PyStackRef ref);
+
 extern bool
 PyStackRef_IsNullOrInt(_PyStackRef ref);
 
@@ -262,6 +265,14 @@ PyStackRef_UntagInt(_PyStackRef i)
 }
 
 
+static inline _PyStackRef
+PyStackRef_IncrementTaggedIntNoOverflow(_PyStackRef ref)
+{
+    assert(ref.bits != (uintptr_t)-1); // Deosn't overflow
+    return (_PyStackRef){ .bits = ref.bits + 4 };
+}
+
+
 #ifdef Py_GIL_DISABLED
 
 #define Py_TAG_DEFERRED (1)
@@ -686,7 +697,13 @@ PyStackRef_XCLOSE(_PyStackRef ref)
 
 #endif // !defined(Py_GIL_DISABLED) && defined(Py_STACKREF_DEBUG)
 
-#define PyStackRef_TYPE(stackref) Py_TYPE(PyStackRef_AsPyObjectBorrow(stackref))
+static inline PyTypeObject *
+PyStackRef_TYPE(_PyStackRef stackref) {
+    if (PyStackRef_IsTaggedInt(stackref)) {
+        return &PyLong_Type;
+    }
+    return Py_TYPE(PyStackRef_AsPyObjectBorrow(stackref));
+}
 
 // Converts a PyStackRef back to a PyObject *, converting the
 // stackref to a new reference.
@@ -697,36 +714,54 @@ PyStackRef_XCLOSE(_PyStackRef ref)
 static inline bool
 PyStackRef_GenCheck(_PyStackRef stackref)
 {
+    if (PyStackRef_IsTaggedInt(stackref)) {
+        return false;
+    }
     return PyGen_Check(PyStackRef_AsPyObjectBorrow(stackref));
 }
 
 static inline bool
 PyStackRef_BoolCheck(_PyStackRef stackref)
 {
+    if (PyStackRef_IsTaggedInt(stackref)) {
+        return false;
+    }
     return PyBool_Check(PyStackRef_AsPyObjectBorrow(stackref));
 }
 
 static inline bool
 PyStackRef_LongCheck(_PyStackRef stackref)
 {
+    if (PyStackRef_IsTaggedInt(stackref)) {
+        return true;
+    }
     return PyLong_Check(PyStackRef_AsPyObjectBorrow(stackref));
 }
 
 static inline bool
 PyStackRef_ExceptionInstanceCheck(_PyStackRef stackref)
 {
+    if (PyStackRef_IsTaggedInt(stackref)) {
+        return false;
+    }
     return PyExceptionInstance_Check(PyStackRef_AsPyObjectBorrow(stackref));
 }
 
 static inline bool
 PyStackRef_CodeCheck(_PyStackRef stackref)
 {
+    if (PyStackRef_IsTaggedInt(stackref)) {
+        return false;
+    }
     return PyCode_Check(PyStackRef_AsPyObjectBorrow(stackref));
 }
 
 static inline bool
 PyStackRef_FunctionCheck(_PyStackRef stackref)
 {
+    if (PyStackRef_IsTaggedInt(stackref)) {
+        return false;
+    }
     return PyFunction_Check(PyStackRef_AsPyObjectBorrow(stackref));
 }