Document new type parameter for AutoReverseDiff (#70)

Author: gdalle

src/dense.jl

@@ -219,7 +219,7 @@ function Base.show(io::IO, backend::AutoPolyesterForwardDiff{chunksize}) where {
 end
 
 """
-    AutoReverseDiff
+    AutoReverseDiff{compile}
 
 Struct used to select the [ReverseDiff.jl](https://github.com/JuliaDiff/ReverseDiff.jl) backend for automatic differentiation.
 
@@ -231,7 +231,7 @@ Defined by [ADTypes.jl](https://github.com/SciML/ADTypes.jl).
 
 # Fields
 
-  - `compile::Union{Val, Bool}`: whether to [compile the tape](https://juliadiff.org/ReverseDiff.jl/api/#ReverseDiff.compile) prior to differentiation
+  - `compile::Union{Val, Bool}`: whether to [compile the tape](https://juliadiff.org/ReverseDiff.jl/api/#ReverseDiff.compile) prior to differentiation (the boolean version is also the type parameter)
 """
 struct AutoReverseDiff{C} <: AbstractADType
     compile::Bool  # this field is left for legacy reasons

test/dense.jl

@@ -115,21 +115,21 @@ end
 @testset "AutoReverseDiff" begin
     ad = @inferred AutoReverseDiff()
     @test ad isa AbstractADType
-    @test ad isa AutoReverseDiff
+    @test ad isa AutoReverseDiff{false}
     @test mode(ad) isa ReverseMode
     @test !ad.compile
     @test_deprecated ad.compile
 
     ad = AutoReverseDiff(; compile = true)
     @test ad isa AbstractADType
-    @test ad isa AutoReverseDiff
+    @test ad isa AutoReverseDiff{true}
     @test mode(ad) isa ReverseMode
     @test ad.compile
     @test_deprecated ad.compile
 
     ad = @inferred AutoReverseDiff(; compile = Val(true))
     @test ad isa AbstractADType
-    @test ad isa AutoReverseDiff
+    @test ad isa AutoReverseDiff{true}
     @test mode(ad) isa ReverseMode
     @test ad.compile
     @test_deprecated ad.compile