some progress on #3832

compiler/parampatterns.nim

@@ -182,6 +182,9 @@ proc isAssignable*(owner: PSym, n: PNode; isUnsafeAddr=false): TAssignableResult
   ## 'owner' can be nil!
   result = arNone
   case n.kind
+  of nkEmpty:
+    if n.typ != nil and n.typ.kind == tyVar:
+      result = arLValue
   of nkSym:
     let kinds = if isUnsafeAddr: {skVar, skResult, skTemp, skParam, skLet}
                 else: {skVar, skResult, skTemp}

compiler/semcall.nim

@@ -420,7 +420,13 @@ proc searchForBorrowProc(c: PContext, startScope: PScope, fn: PSym): PSym =
     let param = fn.typ.n.sons[i]
     let t = skipTypes(param.typ, abstractVar-{tyTypeDesc})
     if t.kind == tyDistinct or param.typ.kind == tyDistinct: hasDistinct = true
-    call.add(newNodeIT(nkEmpty, fn.info, t.baseOfDistinct))
+    var x: PType
+    if param.typ.kind == tyVar:
+      x = newTypeS(tyVar, c)
+      x.addSonSkipIntLit t.baseOfDistinct
+    else:
+      x = t.baseOfDistinct
+    call.add(newNodeIT(nkEmpty, fn.info, x))
   if hasDistinct:
     var resolved = semOverloadedCall(c, call, call, {fn.kind})
     if resolved != nil: