fix: make gpu(x) return unmodified x when GPU backends aren't loa…

…ded (#2295)

* fix: make gpu return unmodified input when gpu isn't available

* add tests

* fix

src/functor.jl

@@ -341,6 +341,7 @@ function gpu(::FluxCUDAAdaptor, x)
         `CUDA.jl` must be loaded to access it.
         Add `using CUDA` or `import CUDA` to your code.
         """ maxlog=1
+        return x
     end
 end
 
@@ -361,6 +362,7 @@ function gpu(::FluxAMDAdaptor, x)
         `AMDGPU.jl` must be loaded to access it.
         Add `using AMDGPU` or `import AMDGPU` to your code.
         """ maxlog=1
+        return x
     end
 end
 
@@ -380,6 +382,7 @@ function gpu(::FluxMetalAdaptor, x)
         The Metal functionality is being called but
         `Metal.jl` must be loaded to access it.
         """ maxlog=1
+        return x
     end
 end
 

test/functors.jl

@@ -0,0 +1,4 @@
+x = rand(Float32, 10, 10)
+if !(Flux.CUDA_LOADED[] || Flux.AMD_LOADED[] || Flux.METAL_LOADED[])
+    @test x === gpu(x)
+end

test/runtests.jl

@@ -56,6 +56,9 @@ Random.seed!(0)
     include("outputsize.jl")
   end
 
+  @testset "functors" begin
+    include("functors.jl")
+  end
 
   if get(ENV, "FLUX_TEST_CUDA", "false") == "true"
     using CUDA