restore return type inference

compiler/ast.nim

@@ -905,6 +905,9 @@ template `{}=`*(n: PNode, i: int, s: PNode): stmt =
 var emptyNode* = newNode(nkEmpty)
 # There is a single empty node that is shared! Do not overwrite it!
 
+proc isMetaType*(t: PType): bool =
+  return t.kind in tyMetaTypes or tfHasMeta in t.flags
+
 proc linkTo*(t: PType, s: PSym): PType {.discardable.} =
   t.sym = s
   s.typ = t

compiler/semexprs.nim

@@ -1164,7 +1164,7 @@ proc semAsgn(c: PContext, n: PNode): PNode =
         if lhsIsResult: {efAllowDestructor} else: {})
     if lhsIsResult:
       n.typ = enforceVoidContext
-      if lhs.sym.typ.kind == tyGenericParam:
+      if lhs.sym.typ.isMetaType:
         if cmpTypes(c, lhs.typ, rhs.typ) == isGeneric:
           internalAssert c.p.resultSym != nil
           lhs.typ = rhs.typ