newruntime: make system.delete and friends work with owned ref (bugfix); reported on the forum

(cherry picked from commit 61c66abbfe)

lib/system.nim

@@ -2111,6 +2111,13 @@ proc add*[T](x: var seq[T], y: openArray[T]) {.noSideEffect.} =
   setLen(x, xl + y.len)
   for i in 0..high(y): x[xl+i] = y[i]
 
+when defined(nimV2):
+  template movingCopy(a, b) =
+    a = move(b)
+else:
+  template movingCopy(a, b) =
+    shallowCopy(a, b)
+
 proc del*[T](x: var seq[T], i: Natural) {.noSideEffect.} =
   ## Deletes the item at index `i` by putting ``x[high(x)]`` into position `i`.
   ##
@@ -2123,7 +2130,7 @@ proc del*[T](x: var seq[T], i: Natural) {.noSideEffect.} =
   ##  var i = @[1, 2, 3, 4, 5]
   ##  i.del(2) # => @[1, 2, 5, 4]
   let xl = x.len - 1
-  shallowCopy(x[i], x[xl])
+  movingCopy(x[i], x[xl])
   setLen(x, xl)
 
 proc delete*[T](x: var seq[T], i: Natural) {.noSideEffect.} =
@@ -2139,7 +2146,7 @@ proc delete*[T](x: var seq[T], i: Natural) {.noSideEffect.} =
   ##  i.delete(2) # => @[1, 2, 4, 5]
   template defaultImpl =
     let xl = x.len
-    for j in i.int..xl-2: shallowCopy(x[j], x[j+1])
+    for j in i.int..xl-2: movingCopy(x[j], x[j+1])
     setLen(x, xl-1)
 
   when nimvm:
@@ -2161,7 +2168,7 @@ proc insert*[T](x: var seq[T], item: T, i = 0.Natural) {.noSideEffect.} =
     setLen(x, xl+1)
     var j = xl-1
     while j >= i:
-      shallowCopy(x[j+1], x[j])
+      movingCopy(x[j+1], x[j])
       dec(j)
   when nimvm:
     defaultImpl()
@@ -3912,9 +3919,9 @@ template spliceImpl(s, a, L, b: untyped): untyped =
   if shift > 0:
     # enlarge:
     setLen(s, newLen)
-    for i in countdown(newLen-1, a+b.len): shallowCopy(s[i], s[i-shift])
+    for i in countdown(newLen-1, a+b.len): movingCopy(s[i], s[i-shift])
   else:
-    for i in countup(a+b.len, newLen-1): shallowCopy(s[i], s[i-shift])
+    for i in countup(a+b.len, newLen-1): movingCopy(s[i], s[i-shift])
     # cut down:
     setLen(s, newLen)
   # fill the hole: