Return nothing for findfirst with empty arrays. (#610)

Author: tam724

src/host/indexing.jl

@@ -191,6 +191,7 @@ Base.getindex(ei::EachIndex, i::Int) = ei.indices[i]
 Base.IndexStyle(::Type{<:EachIndex}) = Base.IndexLinear()
 
 function Base.findfirst(f::Function, A::AnyGPUArray)
+    isempty(A) && return nothing
     indices = EachIndex(A)
     dummy_index = first(indices)
 

test/testsuite.jl

@@ -16,6 +16,7 @@ using Test
 
 using Adapt
 
+test_result(a, b; kwargs...) = a == b
 test_result(a::Number, b::Number; kwargs...) = ≈(a, b; kwargs...)
 test_result(a::Missing, b::Missing; kwargs...) = true
 test_result(a::Number, b::Missing; kwargs...) = false

test/testsuite/indexing.jl

@@ -170,6 +170,10 @@ end
         let x = rand(Float32, 10, 10)
             @test findfirst(>(0.5f0), x) == findfirst(>(0.5f0), AT(x))
         end
+
+        # emtpy
+        @test compare(findfirst, AT, Bool[])
+        @test compare(x->findfirst(>(0.5f0), x), AT, Float32[])
     end
 
     @testset "findmax & findmin" begin