Restrict type broadcast rule to numbers (#1179)

* restrict type broadcast to number

* add a test

Author: mcabbott

Project.toml

@@ -1,6 +1,6 @@
 name = "Zygote"
 uuid = "e88e6eb3-aa80-5325-afca-941959d7151f"
-version = "0.6.35"
+version = "0.6.36"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"

src/lib/broadcast.jl

@@ -144,7 +144,7 @@ end
   end
 end
 
-@adjoint broadcasted(::Type{T}, x::Numeric) where T =
+@adjoint broadcasted(::Type{T}, x::Numeric) where {T<:Number} =
   T.(x), ȳ -> (nothing, _project(x, ȳ),)
 
 # General Fallback

test/gradcheck.jl

@@ -1407,9 +1407,17 @@ end
   @test all(gradient((x,y) -> sum(x .* y), [1,2], [3 4 5]) .≈ ([12, 12], [3 3 3]))
   @test all(gradient((x,y) -> sum(x ./ y), [1,2], 5) .≈ ([0.2, 0.2], -0.12))
 
+  # https://github.com/FluxML/Zygote.jl/pull/1171
   sm = sprand(5, 5, 0.5)
   @test gradient(x -> sum(abs2, Float32.(x)), sm)[1] ≈ gradient(x -> sum(abs2, x), Matrix{Float32}(sm))[1]
   @test gradient(x -> real(sum(ComplexF32.(x) .+ 1 .+ im)), sm)[1] isa SparseMatrixCSC{Float64}
+
+  # https://github.com/FluxML/Zygote.jl/issues/1178
+  function f1179(x)
+    fs = Ref.(x)
+    getindex.(fs)
+  end
+  @test gradient(sum∘f1179, ones(2)) == ([2.0, 2.0],)
 end
 
 using Zygote: Buffer