fixes #7600, generic object with generic ref object parent typerel bug (#7678)

* fixes #7600

* fix wrong logic

compiler/sigmatch.nim

@@ -1388,8 +1388,13 @@ proc typeRelImpl(c: var TCandidate, f, aOrig: PType,
 
         var aAsObject = roota.lastSon
 
-        if fKind in {tyRef, tyPtr} and aAsObject.kind == fKind:
-          aAsObject = aAsObject.base
+        if fKind in {tyRef, tyPtr}:
+          if aAsObject.kind == tyObject:
+            # bug #7600, tyObject cannot be passed
+            # as argument to tyRef/tyPtr
+            return isNone
+          elif aAsObject.kind == fKind:
+            aAsObject = aAsObject.base
 
         if aAsObject.kind == tyObject:
           let baseType = aAsObject.base

tests/typerel/t7600_1.nim

@@ -0,0 +1,18 @@
+discard """
+errormsg: "type mismatch: got <Thin[system.int]>"
+nimout: '''t7600_1.nim(18, 6) Error: type mismatch: got <Thin[system.int]>
+but expected one of:
+proc test[T](x: Paper[T])
+
+expression: test tn'''
+"""
+
+type
+  Paper[T] = ref object of RootObj
+    thickness: T
+  Thin[T]  = object of Paper[T]
+
+proc test[T](x: Paper[T]) = discard
+
+var tn = Thin[int]()
+test tn

tests/typerel/t7600_2.nim

@@ -0,0 +1,17 @@
+discard """
+errormsg: "type mismatch: got <Thin>"
+nimout: '''t7600_2.nim(17, 6) Error: type mismatch: got <Thin>
+but expected one of:
+proc test(x: Paper)
+
+expression: test tn'''
+"""
+
+type
+  Paper = ref object of RootObj
+  Thin  = object of Paper
+
+proc test(x: Paper) = discard
+
+var tn = Thin()
+test tn