[bugfix] fixes #11517

(cherry picked from commit ab36ffbeb1)

tests/destructor/tdestructor3.nim

@@ -5,7 +5,9 @@ destroy
 5
 123
 destroy Foo: 123
-destroy Foo: 5'''
+destroy Foo: 5
+(x1: (val: ...))
+destroy'''
 joinable: false
 """
 
@@ -49,3 +51,45 @@ proc main =
   test(toFooPtr(123))
 
 main()
+
+# bug #11517
+type
+  UniquePtr*[T] = object
+    val: ptr T
+
+proc `=destroy`*[T](p: var UniquePtr[T]) =
+  mixin `=destroy`
+  echo "destroy"
+  if p.val != nil:
+    `=destroy`(p.val[])
+    dealloc(p.val)
+    p.val = nil
+
+proc `=`*[T](dest: var UniquePtr[T], src: UniquePtr[T]) {.error.}
+
+proc `=sink`*[T](dest: var UniquePtr[T], src: UniquePtr[T]) {.inline.} =
+  if dest.val != src.val:
+    if dest.val != nil:
+      `=destroy`(dest)
+    dest.val = src.val
+
+proc newUniquePtr*[T](val: sink T): UniquePtr[T] =
+  result.val = create(T)
+  result.val[] = val
+
+#-------------------------------------------------------------
+
+type
+  MyObject = object of RootObj
+    x1: UniquePtr[int]
+
+  MyObject2 = object of MyObject
+
+proc newObj2(x:int, y: float): MyObject2 =
+  MyObject2(x1: newUniquePtr(x))
+
+proc test =
+  let obj2 = newObj2(1, 1.0)
+  echo obj2
+
+test()