Simplify promote_type_fallback

Author: blegat

src/interface.jl

@@ -25,37 +25,11 @@ function promote_operation_fallback(
     )
 end
 
-_instantiate_zero(::Type{S}) where {S} = zero(S)
-_instantiate_oneunit(::Type{S}) where {S} = oneunit(S)
-
-# this is valid because Irrational numbers are defined in global scope as const
-_instantiate(::Type{S}) where {S<:Irrational} = S()
-_instantiate_zero(::Type{S}) where {S<:AbstractIrrational} = _instantiate(S)
-_instantiate_oneunit(::Type{S}) where {S<:AbstractIrrational} = _instantiate(S)
-
-# Julia v1.0.x has trouble with inference with the `Vararg` method, see
-# https://travis-ci.org/jump-dev/JuMP.jl/jobs/617606373
-function promote_operation_fallback(
-    op::Union{typeof(/),typeof(div)},
-    ::Type{S},
-    ::Type{T},
-) where {S,T}
-    return typeof(op(_instantiate_zero(S), _instantiate_oneunit(T)))
-end
-
-function promote_operation_fallback(
-    op::F,
-    ::Type{S},
-    ::Type{T},
-) where {F<:Function,S,T}
-    return typeof(op(_instantiate_zero(S), _instantiate_zero(T)))
-end
-
 function promote_operation_fallback(
     op::F,
     args::Vararg{Type,N},
 ) where {F<:Function,N}
-    return typeof(op(_instantiate_zero.(args)...))
+    return promote_type(args...)
 end
 
 promote_operation_fallback(::typeof(*), ::Type{T}) where {T} = T