fixes #11660 (#11677)

compiler/semtypinst.nim

@@ -539,7 +539,10 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType =
     let lookup = cl.typeMap.lookup(t)
     if lookup != nil:
       result = lookup
-      if tfUnresolved in t.flags or cl.skipTypedesc: result = result.base
+      if result.kind != tyTypeDesc:
+        result = makeTypeDesc(cl.c, result)
+      elif tfUnresolved in t.flags or cl.skipTypedesc:
+        result = result.base
     elif t.sons[0].kind != tyNone:
       result = makeTypeDesc(cl.c, replaceTypeVarsT(cl, t.sons[0]))
 

tests/misc/tparamsindefault.nim

@@ -18,6 +18,7 @@ f3 10 15 25
 true true
 false true
 world
+typedescDefault
 '''
 """
 
@@ -112,3 +113,8 @@ block:
 
   echo pySubstr("Hello world", -5)
 
+
+# bug #11660
+
+func typedescDefault(T: typedesc; arg: T = 0) = debugEcho "typedescDefault"
+typedescDefault(int)