few notes about the remaining problems with retired buffers

lib/system/sysstr.nim

@@ -213,7 +213,12 @@ proc setLengthSeq(seq: PGenericSeq, elemSize, newLen: int): PGenericSeq {.
           doDecRef(gch.tempStack.d[i], LocalHeap, MaybeCyclic)
         gch.tempStack.len = len0
                           
-    # and set the memory to nil:
+    # XXX: zeroing out the memory can still result in crashes if a wiped-out
+    # cell is aliased by another pointer (ie proc paramter or a let variable).
+    # This is a tought problem, because even if we don't zeroMem here, in the
+    # presense of user defined destructors, the user will expect the cell to be
+    # "destroyed" thus creating the same problem. We can destoy the cell in the
+    # finalizer of the sequence, but this makes destruction non-deterministic.
     zeroMem(cast[pointer](cast[TAddress](result) +% GenericSeqSize +%
            (newLen*%elemSize)), (result.len-%newLen) *% elemSize)
   result.len = newLen