fixes #516

src/tracker/back.jl

@@ -67,7 +67,7 @@ function back!(x, Δ; once = true)
 end
 
 function gradient_(f, xs...)
-  xs = param.(xs)
+  xs = param.(data.(xs))
   l = f(xs...)
   losscheck(l)
   back!(l)
@@ -179,3 +179,5 @@ end
 
 gradient(f, xs...; nest = false) =
   nest ? gradient_nested(f, xs...) : gradient_(f, xs...)
+
+gradient(f, ps::Params) = gradient_nested(f, ps)

test/tracker.jl

@@ -1,6 +1,6 @@
 using Flux
 using Flux.Tracker, Test, NNlib
-using Flux.Tracker: TrackedReal, gradcheck, grad, checkpoint
+using Flux.Tracker: TrackedReal, gradient, gradcheck, grad, checkpoint
 using NNlib: conv, depthwiseconv
 using Printf: @sprintf
 using LinearAlgebra: diagm, dot, LowerTriangular, norm
@@ -260,7 +260,7 @@ Tracker.back!(b)
   back!(z)
   @test grad.((x,y)) == (3, 2)
 
-  @test Tracker.gradient(2, 3) do x, y
+  @test gradient(2, 3) do x, y
     xy = Tracker.collect([x, y])
     xy[1]*xy[2]
   end == (3, 2)
@@ -295,4 +295,12 @@ end
   @test x == 7
 end
 
+@testset "Params" begin
+  W = param(randn(5, 10))
+  x = rand(10)
+  dW = gradient(W -> sum(W*x), W)[1]
+  gs = gradient(() -> sum(W*x), Tracker.Params([W]))
+  @test gs[W] == dW
+end
+
 end #testset