Improve list setitem-slice support

src/runtime/list.cpp

@@ -194,20 +194,51 @@ extern "C" Box* listSetitemInt(BoxedList* self, BoxedInt* slice, Box* v) {
     return None;
 }
 
+Box* listIAdd(BoxedList* self, Box* _rhs);
+
+// Analogue of _PyEval_SliceIndex
+static void sliceIndex(Box* b, int64_t* out) {
+    if (b->cls == none_cls)
+        return;
+
+    RELEASE_ASSERT(b->cls == int_cls, "");
+    *out = static_cast<BoxedInt*>(b)->n;
+}
+
 extern "C" Box* listSetitemSlice(BoxedList* self, BoxedSlice* slice, Box* v) {
     LOCK_REGION(self->lock.asWrite());
 
     assert(self->cls == list_cls);
     assert(slice->cls == slice_cls);
-    i64 start, stop, step;
-    parseSlice(slice, self->size, &start, &stop, &step);
+
+    i64 start = 0, stop = self->size, step = 1;
+
+    sliceIndex(slice->start, &start);
+    sliceIndex(slice->stop, &stop);
+    sliceIndex(slice->step, &step);
+
     RELEASE_ASSERT(step == 1, "step sizes must be 1 for now");
 
-    assert(0 <= start && start < self->size);
-    ASSERT(0 <= stop && stop <= self->size, "%ld %ld", self->size, stop);
-    assert(start <= stop);
+    // Logic from PySequence_GetSlice:
+    if (start < 0)
+        start += self->size;
+    if (stop < 0)
+        stop += self->size;
+
+    // Logic from list_ass_slice:
+    if (start < 0)
+        start = 0;
+    else if (start > self->size)
+        start = self->size;
+
+    if (stop < start)
+        stop = start;
+    else if (stop > self->size)
+        stop = self->size;
+
+    assert(0 <= start && start <= stop && stop <= self->size);
 
-    ASSERT(v->cls == list_cls, "unsupported %s", getTypeName(v)->c_str());
+    RELEASE_ASSERT(v->cls == list_cls, "unsupported %s", getTypeName(v)->c_str());
     BoxedList* lv = static_cast<BoxedList*>(v);
 
     RELEASE_ASSERT(self->elts != lv->elts, "Slice self-assignment currently unsupported");
@@ -260,6 +291,7 @@ extern "C" Box* listDelitemSlice(BoxedList* self, BoxedSlice* slice) {
     parseSlice(slice, self->size, &start, &stop, &step);
     RELEASE_ASSERT(step == 1, "step sizes must be 1 for now");
 
+    // TODO this should reuse listSetitemSlice which does proper index handling
     assert(0 <= start && start < self->size);
     ASSERT(0 <= stop && stop <= self->size, "%ld %ld", self->size, stop);
     assert(start <= stop);

test/tests/list.py

@@ -25,7 +25,7 @@ for i in xrange(-5, 4):
 for i in xrange(-5, 4):
     l3 = range(5)
     l3[:i] = [7, 8]
-    print l3
+    print i, l3
 
 print [1, 2, 3, 4, 5]
 
@@ -87,3 +87,29 @@ class C(object):
 
 # Should not call C().__eq__
 print [C()] == [1, 2]
+
+l2 = l = range(5)
+l3 = range(4)
+l[:] = l3
+print l, l2, l3
+print l is l2
+print l is l3
+
+l = []
+l[:] = range(5)
+print l
+
+for i in xrange(3):
+    for j in xrange(5):
+        l = range(i)
+        l[j:] = ["added"]
+        print i, j, l
+
+        l = range(i)
+        l[:j] = ["added"]
+        print i, j, l
+
+        for k in xrange(5):
+            l = range(i)
+            l[j:k] = ["added"]
+            print i, j, k, l