Allow [0..-1] and [0...0] to work on empty lists.

builtin/core.wren

@@ -10,10 +10,7 @@ class List {
   }
 
   + that {
-    var result = []
-    for (element in this) {
-      result.add(element)
-    }
+    var result = this[0..-1]
     for (element in that) {
       result.add(element)
     }

src/wren_core.c

@@ -53,10 +53,7 @@ static const char* libSource =
 "  }\n"
 "\n"
 "  + that {\n"
-"    var result = []\n"
-"    for (element in this) {\n"
-"      result.add(element)\n"
-"    }\n"
+"    var result = this[0..-1]\n"
 "    for (element in that) {\n"
 "      result.add(element)\n"
 "    }\n"
@@ -389,6 +386,18 @@ DEF_NATIVE(list_subscript)
 
   ObjRange* range = AS_RANGE(args[1]);
 
+  // TODO: This code is pretty hairy. Is there a more elegant way?
+  // Corner case: an empty range at zero is allowed on an empty list.
+  // This way, list[0..-1] and list[0...list.count] can be used to copy a list
+  // even when empty.
+  if (list->count == 0) {
+    if ((range->from == 0 && range->to == -1 && range->isInclusive) ||
+        (range->from == 0 && range->to == 0 && !range->isInclusive))
+    {
+      RETURN_OBJ(wrenNewList(vm, 0));
+    }
+  }
+
   int from = validateIndexValue(vm, args, list->count, range->from,
                                 "Range start");
   if (from == -1) return PRIM_ERROR;

test/list/subscript_range.wren

@@ -29,3 +29,7 @@ IO.print(list[1..-2]) // expect: [b, c, d]
 IO.print(list[2...-1]) // expect: [c, d]
 IO.print(list[4..-5]) // expect: [e, d, c, b, a]
 IO.print(list[3...-6]) // expect: [d, c, b, a]
+
+// An empty range at zero is allowed on an empty list.
+IO.print([][0...0]) // expect: []
+IO.print([][0..-1]) // expect: []