fixed a serious code generation bug leading to wrong RTTI

lib/system/assign.nim

@@ -60,7 +60,7 @@ proc genericAssignAux(dest, src: Pointer, mt: PNimType, shallow: bool) =
       unsureAsgnRef(x, s2)
       return
     sysAssert(dest != nil, "genericAssignAux 3")
-    unsureAsgnRef(x, newObj(mt, seq.len * mt.base.size + GenericSeqSize))
+    unsureAsgnRef(x, newSeq(mt, seq.len))
     var dst = cast[taddress](cast[ppointer](dest)[])
     for i in 0..seq.len-1:
       genericAssignAux(
@@ -68,9 +68,6 @@ proc genericAssignAux(dest, src: Pointer, mt: PNimType, shallow: bool) =
         cast[pointer](cast[taddress](s2) +% i *% mt.base.size +%
                      GenericSeqSize),
         mt.Base, shallow)
-    var dstseq = cast[PGenericSeq](dst)
-    dstseq.len = seq.len
-    dstseq.reserved = seq.len
   of tyObject:
     # we need to copy m_type field for tyObject, as it could be empty for
     # sequence reallocations:
@@ -98,6 +95,35 @@ proc genericShallowAssign(dest, src: Pointer, mt: PNimType) {.compilerProc.} =
   genericAssignAux(dest, src, mt, true)
   GC_enable()
 
+when false:
+  proc debugNimType(t: PNimType) =
+    if t.isNil: 
+      cprintf("nil!")
+      return
+    var k: cstring
+    case t.kind
+    of tyBool: k = "bool"
+    of tyChar: k = "char"
+    of tyEnum: k = "enum"
+    of tyArray: k = "array"
+    of tyObject: k = "object"
+    of tyTuple: k = "tuple"
+    of tyRange: k = "range"
+    of tyPtr: k = "ptr"
+    of tyRef: k = "ref"
+    of tyVar: k = "var"
+    of tySequence: k = "seq"
+    of tyProc: k = "proc"
+    of tyPointer: k = "range"
+    of tyOpenArray: k = "openarray"
+    of tyString: k = "string"
+    of tyCString: k = "cstring"
+    of tyInt: k = "int"
+    of tyInt32: k = "int32"
+    else: k = "other"
+    cprintf("%s %ld\n", k, t.size)
+    debugNimType(t.base)
+
 proc genericSeqAssign(dest, src: Pointer, mt: PNimType) {.compilerProc.} =
   var src = src # ugly, but I like to stress the parser sometimes :-)
   genericAssign(dest, addr(src), mt)