no grad dims helper

src/Flux.jl

@@ -6,7 +6,7 @@ using Base: tail
 using Zygote, MacroTools, Juno, Reexport, Statistics, Random
 using MacroTools: @forward
 @reexport using NNlib
-using Zygote: Params, @adjoint, gradient, pullback
+using Zygote: Params, @adjoint, gradient, pullback, @nograd
 export gradient
 
 export Chain, Dense, Maxout, RNN, LSTM, GRU, Conv, CrossCor, ConvTranspose, MaxPool, MeanPool,

src/layers/conv.jl

@@ -118,6 +118,8 @@ function conv_transpose_dims(c::ConvTranspose, x::AbstractArray)
     )
 end
 
+@nograd conv_transpose_dims
+
 function (c::ConvTranspose)(x::AbstractArray)
   # ndims(x) == ndims(c.weight)-1 && return squeezebatch(c(reshape(x, size(x)..., 1)))
   σ, b = c.σ, reshape(c.bias, map(_->1, c.stride)..., :, 1)

test/layers/conv.jl

@@ -1,5 +1,6 @@
 using Flux, Test
 using Flux: maxpool, meanpool
+using Flux: gradient
 
 @testset "Pooling" begin
   x = randn(Float32, 10, 10, 3, 2)
@@ -54,6 +55,11 @@ end
   y = Conv((3,3), 1 => 1)(x)
   x_hat = ConvTranspose((3, 3), 1 => 1)(y)
   @test size(x_hat) == size(x)
+  m = ConvTranspose((3,3), 2=>1)
+  x = rand(10,10,2,1)
+
+  # Test that the gradient call does not throw: #900
+  @test gradient(()->sum(m(x)), params(m)) isa Flux.Zygote.Grads
 end
 
 @testset "CrossCor" begin