5 files changed, 53 insertions, 25 deletions
diff --git a/lib/system/assign.nim b/lib/system/assign.nim
index 429a92d34..78995954f 100644
--- a/lib/system/assign.nim
+++ b/lib/system/assign.nim
@@ -27,7 +27,7 @@ proc genericAssignAux(dest, src: pointer, n: ptr TNimNode,
     var m = selectBranch(src, n)
     # reset if different branches are in use; note different branches also
     # imply that's not self-assignment (``x = x``)!
-    if m != dd and dd != nil: 
+    if m != dd and dd != nil:
       genericResetAux(dest, dd)
     copyMem(cast[pointer](d +% n.offset), cast[pointer](s +% n.offset),
             n.typ.size)
@@ -205,9 +205,13 @@ proc genericReset(dest: pointer, mt: PNimType) =
   case mt.kind
   of tyString, tyRef, tySequence:
     unsureAsgnRef(cast[PPointer](dest), nil)
-  of tyObject, tyTuple:
-    # we don't need to reset m_type field for tyObject
+  of tyTuple:
+    genericResetAux(dest, mt.node)
+  of tyObject:
     genericResetAux(dest, mt.node)
+    # also reset the type field for tyObject, for correct branch switching!
+    var pint = cast[ptr PNimType](dest)
+    pint[] = nil
   of tyArray, tyArrayConstr:
     for i in 0..(mt.size div mt.base.size)-1:
       genericReset(cast[pointer](d +% i*% mt.base.size), mt.base)
diff --git a/lib/system/excpt.nim b/lib/system/excpt.nim
index 417a8634f..1b3471978 100644
--- a/lib/system/excpt.nim
+++ b/lib/system/excpt.nim
@@ -175,6 +175,8 @@ proc auxWriteStackTrace(f: PFrame, s: var string) =
       add(s, tempFrames[j].procname)
     add(s, "\n")
 
+proc stackTraceAvailable*(): bool
+
 when hasSomeStackTrace:
   proc rawWriteStackTrace(s: var string) =
     when NimStackTrace:
@@ -188,6 +190,18 @@ when hasSomeStackTrace:
       auxWriteStackTraceWithBacktrace(s)
     else:
       add(s, "No stack traceback available\n")
+  proc stackTraceAvailable(): bool =
+    when NimStackTrace:
+      if framePtr == nil:
+        result = false
+      else:
+        result = true
+    elif defined(nativeStackTrace) and nativeStackTraceSupported:
+      result = true
+    else:
+      result = false
+else:
+  proc stackTraceAvailable*(): bool = result = false
 
 proc quitOrDebug() {.inline.} =
   when not defined(endb):
diff --git a/lib/system/gc.nim b/lib/system/gc.nim
index 844f28690..9459ee6b9 100644
--- a/lib/system/gc.nim
+++ b/lib/system/gc.nim
@@ -528,20 +528,9 @@ proc growObj(old: pointer, newsize: int, gch: var TGcHeap): pointer =
   zeroMem(cast[pointer](cast[ByteAddress](res)+% oldsize +% sizeof(TCell)),
           newsize-oldsize)
   sysAssert((cast[ByteAddress](res) and (MemAlign-1)) == 0, "growObj: 3")
-  sysAssert(res.refcount shr rcShift <=% 1, "growObj: 4")
-  #if res.refcount <% rcIncrement:
-  #  add(gch.zct, res)
-  #else: # XXX: what to do here?
-  #  decRef(ol)
-  if (ol.refcount and ZctFlag) != 0:
-    var j = gch.zct.len-1
-    var d = gch.zct.d
-    while j >= 0: 
-      if d[j] == ol:
-        d[j] = res
-        break
-      dec(j)
-  if canbeCycleRoot(ol): excl(gch.cycleRoots, ol)
+  # This can be wrong for intermediate temps that are nevertheless on the
+  # heap because of lambda lifting:
+  #gcAssert(res.refcount shr rcShift <=% 1, "growObj: 4")
   when logGC:
     writeCell("growObj old cell", ol)
     writeCell("growObj new cell", res)
@@ -549,7 +538,26 @@ proc growObj(old: pointer, newsize: int, gch: var TGcHeap): pointer =
   gcTrace(res, csAllocated)
   when reallyDealloc: 
     sysAssert(allocInv(gch.region), "growObj before dealloc")
-    rawDealloc(gch.region, ol)
+    if ol.refcount shr rcShift <=% 1:
+      # free immediately to save space:
+      if (ol.refcount and ZctFlag) != 0:
+        var j = gch.zct.len-1
+        var d = gch.zct.d
+        while j >= 0:
+          if d[j] == ol:
+            d[j] = res
+            break
+          dec(j)
+      if canbeCycleRoot(ol): excl(gch.cycleRoots, ol)
+      rawDealloc(gch.region, ol)
+    else:
+      # we split the old refcount in 2 parts. XXX This is still not entirely
+      # correct if the pointer that receives growObj's result is on the stack.
+      # A better fix would be to emit the location specific write barrier for
+      # 'growObj', but this is lost of more work and who knows what new problems
+      # this would create.
+      res.refcount = rcIncrement
+      decRef(ol)
   else:
     sysAssert(ol.typ != nil, "growObj: 5")
     zeroMem(ol, sizeof(TCell))
diff --git a/lib/system/gc_ms.nim b/lib/system/gc_ms.nim
index 9c3ee8ce2..014b7c278 100644
--- a/lib/system/gc_ms.nim
+++ b/lib/system/gc_ms.nim
@@ -297,10 +297,12 @@ proc growObj(old: pointer, newsize: int, gch: var TGcHeap): pointer =
   zeroMem(cast[pointer](cast[ByteAddress](res)+% oldsize +% sizeof(TCell)),
           newsize-oldsize)
   sysAssert((cast[ByteAddress](res) and (MemAlign-1)) == 0, "growObj: 3")
-  when withBitvectors: excl(gch.allocated, ol)
-  when reallyDealloc: rawDealloc(gch.region, ol)
-  else:
-    zeroMem(ol, sizeof(TCell))
+  when false:
+    # this is wrong since seqs can be shared via 'shallow':
+    when withBitvectors: excl(gch.allocated, ol)
+    when reallyDealloc: rawDealloc(gch.region, ol)
+    else:
+      zeroMem(ol, sizeof(TCell))
   when withBitvectors: incl(gch.allocated, res)
   when useCellIds:
     inc gch.idGenerator
diff --git a/lib/system/repr.nim b/lib/system/repr.nim
index 2de603cea..5a243cb44 100644
--- a/lib/system/repr.nim
+++ b/lib/system/repr.nim
@@ -78,7 +78,7 @@ proc reprEnum(e: int, typ: PNimType): string {.compilerRtl.} =
 type
   PByteArray = ptr array[0.. 0xffff, int8]
 
-proc addSetElem(result: var string, elem: int, typ: PNimType) {.gcsafe.} =
+proc addSetElem(result: var string, elem: int, typ: PNimType) {.benign.} =
   case typ.kind
   of tyEnum: add result, reprEnum(elem, typ)
   of tyBool: add result, reprBool(bool(elem))
@@ -147,7 +147,7 @@ when not defined(useNimRtl):
     for i in 0..cl.indent-1: add result, ' '
 
   proc reprAux(result: var string, p: pointer, typ: PNimType,
-               cl: var TReprClosure) {.gcsafe.}
+               cl: var TReprClosure) {.benign.}
 
   proc reprArray(result: var string, p: pointer, typ: PNimType,
                  cl: var TReprClosure) =
@@ -172,7 +172,7 @@ when not defined(useNimRtl):
     add result, "]"
 
   proc reprRecordAux(result: var string, p: pointer, n: ptr TNimNode,
-                     cl: var TReprClosure) {.gcsafe.} =
+                     cl: var TReprClosure) {.benign.} =
     case n.kind
     of nkNone: sysAssert(false, "reprRecordAux")
     of nkSlot: