fix #5658

compiler/semstmts.nim

@@ -851,9 +851,12 @@ proc typeSectionFinalPass(c: PContext, n: PNode) =
         # type aliases are hard:
         var t = semTypeNode(c, x, nil)
         assert t != nil
-        if t.kind in {tyObject, tyEnum, tyDistinct}:
-          assert s.typ != nil
-          if s.typ.kind != tyAlias:
+        if s.typ != nil and s.typ.kind != tyAlias:
+          if t.kind in {tyProc, tyGenericInst} and not t.isMetaType:
+            assignType(s.typ, t)
+            s.typ.id = t.id
+          elif t.kind in {tyObject, tyEnum, tyDistinct}:
+            assert s.typ != nil
             assignType(s.typ, t)
             s.typ.id = t.id     # same id
       checkConstructedType(s.info, s.typ)

compiler/semtypes.nim

@@ -893,7 +893,13 @@ proc liftParamType(c: PContext, procKind: TSymKind, genericParams: PNode,
       let lifted = liftingWalk(paramType.sons[i])
       if lifted != nil: paramType.sons[i] = lifted
 
-    if paramType.base.lastSon.kind == tyUserTypeClass:
+    let body = paramType.base
+    if body.kind == tyForward:
+      # this may happen for proc type appearing in a type section
+      # before one of its param types
+      return
+
+    if body.lastSon.kind == tyUserTypeClass:
       let expanded = instGenericContainer(c, info, paramType,
                                           allowMetaTypes = true)
       result = liftingWalk(expanded, true)
@@ -1067,6 +1073,7 @@ proc semBlockType(c: PContext, n: PNode, prev: PType): PType =
 
 proc semGenericParamInInvocation(c: PContext, n: PNode): PType =
   result = semTypeNode(c, n, nil)
+  n.typ = makeTypeDesc(c, result)
 
 proc semObjectTypeForInheritedGenericInst(c: PContext, n: PNode, t: PType) =
   var