Fix complex number promotion

Author: mtfishman

NDTensors/src/emptynumber.jl

@@ -18,10 +18,13 @@ convert(::Type{T}, x::EmptyNumber) where {T<:Number} = T(zero(T))
 # This helps with defining `norm` of `EmptyStorage{EmptyNumber}`.
 AbstractFloat(::EmptyNumber) = zero(AbstractFloat)
 
-Base.promote_rule(::Type{EmptyNumber}, ::Type{T}) where {T<:Number} = T
-Base.promote_rule(::Type{T}, ::Type{EmptyNumber}) where {T<:Number} = T
+# Extra definitions fix ambiguity errors.
+Base.promote_rule(::Type{EmptyNumber}, T::Type{<:Number}) = T
+Base.promote_rule(T::Type{<:Number}, ::Type{EmptyNumber}) = T
 Base.promote_rule(::Type{EmptyNumber}, ::Type{Bool}) = Bool
 Base.promote_rule(::Type{Bool}, ::Type{EmptyNumber}) = Bool
+Base.promote_rule(::Type{EmptyNumber}, T::Type{Complex{R}}) where {R<:Real} = T
+Base.promote_rule(T::Type{Complex{R}}, ::Type{EmptyNumber}) where {R<:Real} = T
 
 # Basic arithmetic
 (::EmptyNumber + ::EmptyNumber) = EmptyNumber()

NDTensors/test/test_emptynumber.jl

@@ -12,7 +12,7 @@ const 𝟎 = EmptyNumber()
   @test complex(EmptyNumber) == Complex{EmptyNumber}
 
   # Promotion
-  for T in (Bool, Float64)
+  for T in (Bool, Float32, Float64, Complex{Float32}, Complex{Float64})
     @test promote_type(EmptyNumber, T) === T
     @test promote_type(T, EmptyNumber) === T
   end