remove AbstractArrayStyle type piracy

Author: marius311

base/broadcast.jl

@@ -137,12 +137,6 @@ BroadcastStyle(a::AbstractArrayStyle, ::Style{Tuple})    = a
 BroadcastStyle(::A, ::A) where A<:ArrayStyle             = A()
 BroadcastStyle(::ArrayStyle, ::ArrayStyle)               = Unknown()
 BroadcastStyle(::A, ::A) where A<:AbstractArrayStyle     = A()
-Base.@pure function BroadcastStyle(a::A, b::B) where {A<:AbstractArrayStyle{M},B<:AbstractArrayStyle{N}} where {M,N}
-    if Base.typename(A) === Base.typename(B)
-        return A(Val(max(M, N)))
-    end
-    return Unknown()
-end
 # Any specific array type beats DefaultArrayStyle
 BroadcastStyle(a::AbstractArrayStyle{Any}, ::DefaultArrayStyle) = a
 BroadcastStyle(a::AbstractArrayStyle{N}, ::DefaultArrayStyle{N}) where N = a

test/broadcast.jl

@@ -929,3 +929,9 @@ ret =  @macroexpand @.([Int, Number] <: Real)
 
 ret =  @macroexpand @.([Int, Number] >: Real)
 @test ret == :([Int, Number] .>: Real)
+
+
+struct CustomStyle{T} <: Broadcast.AbstractArrayStyle{1} end
+Broadcast.BroadcastStyle(::CustomStyle{:A}, ::CustomStyle{:B}) = CustomStyle{:A}()
+@test Broadcast.result_style(CustomStyle{:A}(), CustomStyle{:B}()) ==
+      Broadcast.result_style(CustomStyle{:B}(), CustomStyle{:A}()) == CustomStyle{:A}()