fixes #3544

compiler/semexprs.nim

@@ -87,8 +87,9 @@ type
     convNotNeedeed,
     convNotLegal
 
-proc checkConversionBetweenObjects(castDest, src: PType): TConvStatus =
-  return if inheritanceDiff(castDest, src) == high(int):
+proc checkConversionBetweenObjects(castDest, src: PType; pointers: int): TConvStatus =
+  let diff = inheritanceDiff(castDest, src)
+  return if diff == high(int) or (pointers > 1 and diff != 0):
       convNotLegal
     else:
       convOK
@@ -105,13 +106,15 @@ proc checkConvertible(c: PContext, castDest, src: PType): TConvStatus =
     return
   var d = skipTypes(castDest, abstractVar)
   var s = skipTypes(src, abstractVar-{tyTypeDesc})
+  var pointers = 0
   while (d != nil) and (d.kind in {tyPtr, tyRef}) and (d.kind == s.kind):
     d = d.lastSon
     s = s.lastSon
+    inc pointers
   if d == nil:
     result = convNotLegal
   elif d.kind == tyObject and s.kind == tyObject:
-    result = checkConversionBetweenObjects(d, s)
+    result = checkConversionBetweenObjects(d, s, pointers)
   elif (skipTypes(castDest, abstractVarRange).kind in IntegralTypes) and
       (skipTypes(src, abstractVarRange-{tyTypeDesc}).kind in IntegralTypes):
     # accept conversion between integral types

compiler/sigmatch.nim

@@ -598,6 +598,10 @@ proc tryResolvingStaticExpr(c: var TCandidate, n: PNode): PNode =
   let instantiated = replaceTypesInBody(c.c, c.bindings, n, nil)
   result = c.c.semExpr(c.c, instantiated)
 
+template subtypeCheck() =
+  if result <= isSubrange and f.lastSon.skipTypes(abstractInst).kind in {tyRef, tyPtr, tyVar}:
+    result = isNone
+
 proc typeRel(c: var TCandidate, f, aOrig: PType, doBind = true): TTypeRelation =
   # typeRel can be used to establish various relationships between types:
   #
@@ -737,6 +741,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType, doBind = true): TTypeRelation =
   of tyVar:
     if aOrig.kind == tyVar: result = typeRel(c, f.base, aOrig.base)
     else: result = typeRel(c, f.base, aOrig)
+    subtypeCheck()
   of tyArray, tyArrayConstr:
     # tyArrayConstr cannot happen really, but
     # we wanna be safe here
@@ -867,6 +872,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType, doBind = true): TTypeRelation =
       for i in 0..f.len-2:
         if typeRel(c, f.sons[i], a.sons[i]) == isNone: return isNone
       result = typeRel(c, f.lastSon, a.lastSon)
+      subtypeCheck()
       if result <= isConvertible: result = isNone
       elif tfNotNil in f.flags and tfNotNil notin a.flags:
         result = isNilConversion