objlist: Implement growing slice assignment.

This means that complete slice operations are supported for lists (but not
for bytearray's and array.array's).

py/obj.h

@@ -578,3 +578,8 @@ mp_obj_t mp_seq_count_obj(const mp_obj_t *items, uint len, mp_obj_t value);
     memcpy(dest + beg, slice, slice_len * sizeof(item_t)); \
     /*printf("memcpy(%p, %p, %d)\n", dest + (beg + slice_len), dest + end, (dest_len - end) * sizeof(item_t));*/ \
     memcpy(dest + (beg + slice_len), dest + end, (dest_len - end) * sizeof(item_t));
+
+#define mp_seq_replace_slice_grow_inplace(dest, dest_len, beg, end, slice, slice_len, len_adj, item_t) \
+    /*printf("memmove(%p, %p, %d)\n", dest + beg + len_adj, dest + beg, (dest_len - beg) * sizeof(item_t));*/ \
+    memmove(dest + beg + len_adj, dest + beg, (dest_len - beg) * sizeof(item_t)); \
+    memcpy(dest + beg, slice, slice_len * sizeof(item_t));

py/objlist.c

@@ -199,12 +199,21 @@ STATIC mp_obj_t list_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
             }
             int len_adj = slice->len - (stop - start);
             //printf("Len adj: %d\n", len_adj);
-            assert(len_adj <= 0);
-            mp_seq_replace_slice_no_grow(self->items, self->len, start, stop, slice->items, slice->len, mp_obj_t);
-            // Clear "freed" elements at the end of list
-            mp_seq_clear(self->items, self->len + len_adj, self->len, sizeof(*self->items));
+            if (len_adj > 0) {
+                if (self->len + len_adj > self->alloc) {
+                    // TODO: Might optimize memory copies here by checking if block can
+                    // be grown inplace or not
+                    self->items = m_renew(mp_obj_t, self->items, self->alloc, self->len + len_adj);
+                    self->alloc = self->len + len_adj;
+                }
+                mp_seq_replace_slice_grow_inplace(self->items, self->len, start, stop, slice->items, slice->len, len_adj, mp_obj_t);
+            } else {
+                mp_seq_replace_slice_no_grow(self->items, self->len, start, stop, slice->items, slice->len, mp_obj_t);
+                // Clear "freed" elements at the end of list
+                mp_seq_clear(self->items, self->len + len_adj, self->len, sizeof(*self->items));
+                // TODO: apply allocation policy re: alloc_size
+            }
             self->len += len_adj;
-            // TODO: apply allocation policy re: alloc_size
             return mp_const_none;
         }
 #endif

tests/basics/list_slice_assign_grow.py

+x = list(range(2))
+
+l = list(x)
+l[0:0] = [10]
+print(l)
+l = list(x)
+l[:0] = [10, 20]
+print(l)
+l = list(x)
+l[0:0] = [10, 20, 30, 40]
+print(l)
+
+l = list(x)
+l[1:1] = [10, 20, 30, 40]
+print(l)
+
+l = list(x)
+l[2:] = [10, 20, 30, 40]
+print(l)
+
+# Weird cases
+l = list(x)
+l[1:0] = [10, 20, 30, 40]
+print(l)
+
+l = list(x)
+l[100:100] = [10, 20, 30, 40]
+print(l)