define equality for CRC.ZeroTangent

Author: oxinabox

src/extra_rules.jl

@@ -287,3 +287,8 @@ function ChainRulesCore.frule((_, ȯbj, _, ẋ), ::typeof(setproperty!), obj::M
     ẏ = setproperty!(ȯbj, field, ẋ)
     return y, ẏ
 end
+
+# https://github.com/JuliaDiff/ChainRulesCore.jl/issues/607
+Base.:(==)(x::Number, ::ZeroTangent) = iszero(x)
+Base.:(==)(::ZeroTangent, x::Number) = iszero(x)
+Base.hash(x::ZeroTangent, h::UInt64) = hash(0, h)

src/stage1/forward.jl

@@ -40,7 +40,7 @@ function shuffle_up(r::TaylorBundle{1, Tuple{B1,B2}}) where {B1,B2}
     z₂ = primal(r)[2]
     z₁₂ = partial(r, 1)[2]
     if true
-        @assert z₁ == z₂
+        @assert(z₁ == z₂,  "$z₁ == $z₂")
         return TaylorBundle{2}(z₀, (z₁, z₁₂))
     else
         return ExplicitTangentBundle{2}(z₀, (z₁, z₂, z₁₂))