fix FluxML#16

src/functor.jl

@@ -192,11 +192,12 @@ julia> fcollect(m, exclude = v -> Functors.isleaf(v))
  Bar([1, 2, 3])
 ```
 """
-function fcollect(x; cache = [], exclude = v -> false)
-  x in cache && return cache
-  if !exclude(x)
-    push!(cache, x)
-    foreach(y -> fcollect(y; cache = cache, exclude = exclude), children(x))
-  end
-  return cache
+function fcollect(x; output = [], cache = Base.IdSet(), exclude = v -> false)
+    x in cache && return output
+    if !exclude(x)
+      push!(cache, x)
+      push!(output, x)
+      foreach(y -> fcollect(y; cache=cache, output=output, exclude=exclude), children(x))
+    end
+    return output
 end

test/basics.jl

@@ -84,6 +84,11 @@ end
   m3 = Foo(m2, m0)
   m4 = Bar(m3)
   @test all(fcollect(m4) .=== [m4, m3, m2, m1, m0])
+
+  m1 = [1, 2, 3]
+  m2 = [1, 2, 3]
+  m3 = Foo(m1, m2)
+  @test all(fcollect(m3) .=== [m3, m1, m2])
 end
 
 struct FFoo