support for inferring static[T] concept params

compiler/ast.nim

@@ -490,6 +490,7 @@ type
     tfHasStatic
     tfGenericTypeParam
     tfImplicitTypeParam
+    tfInferrableStatic
     tfWildcard        # consider a proc like foo[T, I](x: Type[T, I])
                       # T and I here can bind to both typedesc and static types
                       # before this is determined, we'll consider them to be a
@@ -1073,6 +1074,9 @@ proc isMetaType*(t: PType): bool =
          (t.kind == tyStatic and t.n == nil) or
          tfHasMeta in t.flags
 
+proc isUnresolvedStatic*(t: PType): bool =
+  return t.kind == tyStatic and t.n == nil
+
 proc linkTo*(t: PType, s: PSym): PType {.discardable.} =
   t.sym = s
   s.typ = t