vm,py: fix generators called after end of code

Author: ncw

py/generator.go

@@ -85,6 +85,10 @@ func (it *Generator) Send(arg Object) Object {
 			panic(ExceptionNewf(TypeError, "can't send non-None value to a just-started generator"))
 		}
 	} else {
+		// If already returned a non yield value then stop
+		if !it.Frame.Yielded {
+			panic(StopIteration)
+		}
 		// Push arg onto the frame's value stack
 		it.Frame.Stack = append(it.Frame.Stack, arg)
 	}

vm/eval.go

@@ -1639,6 +1639,22 @@ func RunFrame(frame *py.Frame) (res py.Object, err error) {
 	// 	}
 	// }()
 
+	// FIXME
+	// if (co->co_flags & CO_GENERATOR) {
+	//     if (!throwflag && f->f_exc_type != NULL && f->f_exc_type != Py_None) {
+	//         /* We were in an except handler when we left,
+	//            restore the exception state which was put aside
+	//            (see YIELD_VALUE). */
+	//         swap_exc_state(tstate, f);
+	//     }
+	//     else
+	//         save_exc_state(tstate, f);
+	// }
+
+	if int(frame.Lasti) >= len(frame.Code.Code) {
+		panic(py.ExceptionNewf(py.SystemError, "vm: instruction out of range - code most likely finished already"))
+	}
+
 	var opcode OpCode
 	var arg int32
 	for vm.why == whyNot {

vm/tests/generators.py

@@ -7,12 +7,13 @@ def g1():
 assert next(i) == 1
 assert next(i) == 2
 assert next(i) == 3
-ok = False
-try:
-    next(i)
-except StopIteration:
-    ok = True
-assert ok, "StopIteration not raised"
+for _ in (1, 2):
+    ok = False
+    try:
+        next(i)
+    except StopIteration:
+        ok = True
+    assert ok, "StopIteration not raised"
 
 doc="generator 2"
 def g2():