test: add proper empty tests

Author: gdalle

DifferentiationInterface/src/utils/batchsize.jl

@@ -6,7 +6,7 @@ Configuration for the batch size deduced from a backend and a sample array of le
 # Type parameters
 
   - `B::Int`: batch size
-  - `singlebatch::Bool`: whether `B == N` (`B > N` is not allowed)
+  - `singlebatch::Bool`: whether `B == N` (`B > N` is only allowed when `N == 0`)
   - `aligned::Bool`: whether `N % B == 0`
 
 # Fields
@@ -127,7 +127,9 @@ Reproduces the heuristic from ForwardDiff to minimize
 Source: https://github.com/JuliaDiff/ForwardDiff.jl/blob/ec74fbc32b10bbf60b3c527d8961666310733728/src/prelude.jl#L19-L29
 """
 function reasonable_batchsize(N::Integer, Bmax::Integer)
-    if N <= Bmax
+    if N == 0
+        return 1
+    elseif N <= Bmax
         return N
     else
         A = div(N, Bmax, RoundUp)

DifferentiationInterface/test/Back/Enzyme/test.jl

@@ -201,3 +201,11 @@ end
         @test occursin("DifferentiationInterface", msg)
     end
 end
+
+@testset "Empty arrays" begin
+    test_differentiation(
+        [AutoEnzyme(; mode=Enzyme.Forward), AutoEnzyme(; mode=Enzyme.Reverse)],
+        empty_scenarios();
+        excluded=[:jacobian],
+    )
+end;

DifferentiationInterface/test/Core/Internals/batchsize.jl

@@ -13,6 +13,7 @@ using Test
 BSS = BatchSizeSettings
 
 @testset "Default" begin
+    @test (@inferred pick_batchsize(AutoZygote(), zeros(0))) isa BSS{1,false,true}
     @test (@inferred pick_batchsize(AutoZygote(), zeros(2))) isa BSS{1,false,true}
     @test (@inferred pick_batchsize(AutoZygote(), zeros(100))) isa BSS{1,false,true}
     @test_throws ArgumentError pick_batchsize(AutoSparse(AutoZygote()), zeros(2))
@@ -25,7 +26,7 @@ BSS = BatchSizeSettings
 end
 
 @testset "SimpleFiniteDiff (adaptive)" begin
-    @test (pick_batchsize(AutoSimpleFiniteDiff(), zeros(0))) isa BSS{0,true,true}
+    @test (pick_batchsize(AutoSimpleFiniteDiff(), zeros(0))) isa BSS{1,false,true}
     @test (pick_batchsize(AutoSimpleFiniteDiff(), zeros(2))) isa BSS{2,true,true}
     @test (pick_batchsize(AutoSimpleFiniteDiff(), zeros(6))) isa BSS{6,true,true}
     @test (pick_batchsize(AutoSimpleFiniteDiff(), zeros(12))) isa BSS{12,true,true}

DifferentiationInterface/test/Core/ZeroBackends/test.jl

@@ -53,13 +53,7 @@ end
 end
 
 @testset "Empty arrays" begin
-    make_empty(t) = typeof(t)[]
-    make_empty!(y, t) = nothing
-    @test gradient(sum, AutoZeroForward(), Float64[]) == Float64[]
-    @test derivative(make_empty, AutoZeroReverse(), 1.0) == Float64[]
-    @test derivative(make_empty!, Float64[], AutoZeroReverse(), 1.0) == Float64[]
-    @test_broken jacobian(copy, AutoZeroForward(), Float64[]) == I(0)
-    @test_broken jacobian(copy, AutoZeroReverse(), Float64[]) == I(0)
-    @test_broken jacobian(copyto!, Float64[], AutoZeroForward(), Float64[]) == I(0)
-    @test_broken jacobian(copyto!, Float64[], AutoZeroReverse(), Float64[]) == I(0)
-end
+    test_differentiation(
+        [AutoZeroForward(), AutoZeroReverse()], empty_scenarios(); excluded=[:jacobian]
+    )
+end;

DifferentiationInterface/test/testutils.jl

@@ -10,7 +10,8 @@ using DifferentiationInterfaceTest:
     complex_sparse_scenarios,
     static_scenarios,
     component_scenarios,
-    gpu_scenarios
+    gpu_scenarios,
+    empty_scenarios
 
 function MyAutoSparse(backend::AbstractADType)
     return AutoSparse(

DifferentiationInterfaceTest/src/DifferentiationInterfaceTest.jl

@@ -93,7 +93,7 @@ using DifferentiationInterface: Rewrap, Context, Constant, Cache, ConstantOrCach
 using DifferentiationInterface: PreparationMismatchError
 using DocStringExtensions: TYPEDFIELDS, TYPEDSIGNATURES
 using JET: @test_opt
-using LinearAlgebra: Adjoint, Diagonal, Transpose, dot, parent
+using LinearAlgebra: Adjoint, Diagonal, Transpose, I, dot, parent
 using ProgressMeter: ProgressUnknown, next!
 using Random: AbstractRNG, default_rng, rand!
 using SparseArrays:
@@ -124,6 +124,7 @@ include("scenarios/default.jl")
 include("scenarios/sparse.jl")
 include("scenarios/complex.jl")
 include("scenarios/allocfree.jl")
+include("scenarios/empty.jl")
 include("scenarios/extensions.jl")
 
 include("tests/correctness_eval.jl")

DifferentiationInterfaceTest/src/scenarios/empty.jl

@@ -0,0 +1,16 @@
+make_empty(t::Number) = typeof(t)[]
+function make_empty!(y::AbstractArray, t::Number)
+    @assert isempty(y)
+    return nothing
+end
+
+function empty_scenarios()
+    scens = Scenario[
+        Scenario{:derivative,:out}(make_empty, 1.0; res1=Float64[]),
+        Scenario{:derivative,:out}(make_empty!, Float64[], 1.0; res1=Float64[]),
+        Scenario{:gradient,:out}(sum, Float64[]; res1=Float64[]),
+        Scenario{:jacobian,:out}(copy, Float64[]; res1=float.(I(0))),
+        Scenario{:jacobian,:out}(copyto!, Float64[], Float64[]; res1=float.(I(0))),
+    ]
+    return scens
+end

DifferentiationInterfaceTest/test/runtests.jl

@@ -12,7 +12,8 @@ using DifferentiationInterfaceTest:
     complex_sparse_scenarios,
     static_scenarios,
     component_scenarios,
-    gpu_scenarios
+    gpu_scenarios,
+    empty_scenarios
 
 GROUP = get(ENV, "JULIA_DIT_TEST_GROUP", "All")
 

DifferentiationInterfaceTest/test/standard.jl

@@ -28,6 +28,13 @@ test_differentiation(
     logging=LOGGING,
 )
 
+test_differentiation(
+    [AutoForwardDiff()], empty_scenarios(); excluded=[:gradient], logging=LOGGING
+)
+test_differentiation(
+    [AutoFiniteDiff()], empty_scenarios(); excluded=[:jacobian], logging=LOGGING
+)
+
 ## Sparse
 
 sparse_backend = AutoSparse(