implement promote for BitArray

Fix #43551
Co-authored-by: Jakob Sachs <[email protected]>

base/array.jl

@@ -614,7 +614,7 @@ oneunit(x::AbstractMatrix{T}) where {T} = _one(oneunit(T), x)
 convert(::Type{T}, a::AbstractArray) where {T<:Array} = a isa T ? a : T(a)
 convert(::Type{Union{}}, a::AbstractArray) = throw(MethodError(convert, (Union{}, a)))
 
-promote_rule(a::Type{Array{T,n}}, b::Type{Array{S,n}}) where {T,n,S} = el_same(promote_type(T,S), a, b)
+promote_rule(a::Type{<:AbstractArray{T,n}}, b::Type{<:AbstractArray{S,n}}) where {T,n,S} = el_same(promote_type(T, S), a, b)
 
 ## Constructors ##
 

base/range.jl

@@ -1265,7 +1265,7 @@ end
 
 
 # promote eltype if at least one container wouldn't change, otherwise join container types.
-el_same(::Type{T}, a::Type{<:AbstractArray{T,n}}, b::Type{<:AbstractArray{T,n}}) where {T,n}   = a
+el_same(::Type{T}, a::Type{<:AbstractArray{T,n}}, b::Type{<:AbstractArray{T,n}}) where {T,n}   = a === b ? a : Array{T,n}
 el_same(::Type{T}, a::Type{<:AbstractArray{T,n}}, b::Type{<:AbstractArray{S,n}}) where {T,S,n} = a
 el_same(::Type{T}, a::Type{<:AbstractArray{S,n}}, b::Type{<:AbstractArray{T,n}}) where {T,S,n} = b
 el_same(::Type, a, b) = promote_typejoin(a, b)

test/bitarray.jl

@@ -98,6 +98,18 @@ end
 
 timesofar("conversions")
 
+@testset "Promotions for size $sz" for (sz, T) in allsizes
+    @test isequal(promote(falses(sz...),zeros(sz...)),
+                 (zeros(sz...),zeros(sz...)))
+    @test isequal(promote(trues(sz...),ones(sz...)),
+                 (ones(sz...),ones(sz...)))
+    ae = falses(1,sz...)
+    @test_throws ErrorException promote(ae,ones(sz...))
+    @test_throws ErrorException promote(ae,[ones(sz...)])
+end
+
+timesofar("promotions")
+
 @testset "utility functions" begin
     b1 = bitrand(v1)
     @test isequal(fill!(b1, true), trues(size(b1)))
@@ -1767,4 +1779,4 @@ end
         @test all(bitarray[rangeout, rangein] .== true)
         @test all(bitarray[rangein, rangeout] .== true)
     end
-end
+end