.n.isNil checks for tyTuple PTypes.

compiler/evalffi.nim

@@ -164,6 +164,7 @@ proc packObject(x: PNode, typ: PType, res: pointer) =
       let field = getField(typ.n, i)
       pack(it, field.typ, res +! field.offset)
     else:
+      # XXX: todo
       globalError(x.info, "cannot pack unnamed tuple")
 
 const maxPackDepth = 20

compiler/sempass2.nim

@@ -138,7 +138,7 @@ proc guardDotAccess(a: PEffects; n: PNode) =
   if g.kind == skUnknown:
     var field: PSym = nil
     var ty = n.sons[0].typ.skipTypes(abstractPtrs)
-    if ty.kind == tyTuple:
+    if ty.kind == tyTuple and not ty.n.isNil:
       field = lookupInRecord(ty.n, g.name)
     else:
       while ty != nil and ty.kind == tyObject:

compiler/semstmts.nim

@@ -692,7 +692,7 @@ proc typeSectionFinalPass(c: PContext, n: PNode) =
           assignType(s.typ, t)
           s.typ.id = t.id     # same id
       checkConstructedType(s.info, s.typ)
-      if s.typ.kind in {tyObject, tyTuple}:
+      if s.typ.kind in {tyObject, tyTuple} and not s.typ.n.isNil:
         checkForMetaFields(s.typ.n)
     let aa = a.sons[2]
     if aa.kind in {nkRefTy, nkPtrTy} and aa.len == 1 and

compiler/semtypinst.nim

@@ -341,6 +341,8 @@ proc skipIntLiteralParams*(t: PType) =
 proc propagateFieldFlags(t: PType, n: PNode) =
   # This is meant for objects and tuples
   # The type must be fully instantiated!
+  if n.isNil:
+    return
   internalAssert n.kind != nkRecWhen
   case n.kind
   of nkSym: