Fix list reversal

lst->data is NULL for a 0 length list, which we can't copy, so got to
check!

And for reversed() we have to actually return the reversed copy of the
list, not the original! ;)

Add some tests for it...

CHANGELOG.md

@@ -69,6 +69,9 @@
 - Fix module import check [#1420]
 - Avoid segfault when exception `error_message` is not set [#1422]
 - Bump Zig version to v0.11.0 [#1421]
+- Fix `reversed([])` which would `SIGILL` in dev mode [#1455]
+- Fix `reversed([1,2,3])` which now returns reversed result [#1455]
+  - Previous code did the reversal but returned the original value :P
 
 
 ## [0.16.0] (2023-07-03)

base/builtin/list.c

@@ -140,7 +140,8 @@ B_list B_listD_copy(B_list lst) {
     int len = lst->length;
     B_list res = B_listD_new(len);
     res->length = len;
-    memcpy(res->data, lst->data, len*sizeof($WORD));
+    if (len > 0)
+        memcpy(res->data, lst->data, len*sizeof($WORD));
     return res;
 }
 
@@ -447,8 +448,8 @@ B_NoneType B_SequenceD_listD_reverse(B_SequenceD_list wit, B_list lst) {
 
 B_Iterator B_SequenceD_listD___reversed__(B_SequenceD_list wit, B_list lst) {
     B_list copy = B_listD_copy(lst);
-    B_SequenceD_listD_reverse(wit,copy);
-    return B_CollectionD_SequenceD_listD___iter__((B_CollectionD_SequenceD_list)wit->W_Collection, lst);
+    B_SequenceD_listD_reverse(wit, copy);
+    return B_CollectionD_SequenceD_listD___iter__((B_CollectionD_SequenceD_list)wit->W_Collection, copy);
 }
 
 B_NoneType B_SequenceD_listD_insert(B_SequenceD_list wit, B_list lst, B_int n, $WORD elem) {

test/builtins_auto/list.act

@@ -43,6 +43,21 @@ actor main(env):
         print("Unexpected result of list.reverse():", l)
         await async env.exit(1)
 
+    lr = list(reversed([]))
+    if lr != []:
+        print("Unexpected result of reversed([]):", lr)
+        await async env.exit(1)
+
+    lr2 = list(reversed([1]))
+    if lr2 != [1]:
+        print("Unexpected result of reversed([]):", lr2)
+        await async env.exit(1)
+
+    lr3 = list(reversed([1,2,3]))
+    if lr3 != [3,2,1]:
+        print("Unexpected result of reversed([1,2,3]):", lr3)
+        await async env.exit(1)
+
     del l[1]
     if l != [56, 3, 2, 37, 1, 0]:
         print("Unexpected result of del list[1]:", l)