implement promote for BitArray

Defines a fallback promote_result for any AbstractArray, for the case
when specific promote_rules are not defined for the specific array type.

Add a few good promote_rules too.

Fix #43551
Co-authored-by: Jakob Sachs <jakobsachs1999@gmail.com>

base/array.jl

@@ -617,7 +617,7 @@ 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{<:Array{T,n}}, b::Type{<:Array{S,n}}) where {T,n,S} = el_same(promote_type(T, S), a, b)
 
 ## Constructors ##
 

base/indices.jl

@@ -351,6 +351,8 @@ struct Slice{T<:AbstractUnitRange} <: AbstractUnitRange{Int}
     indices::T
 end
 Slice(S::Slice) = S
+Slice{T}(S::Slice) where {T<:AbstractUnitRange} = Slice{T}(T(S.indices))
+
 axes(S::Slice) = (IdentityUnitRange(S.indices),)
 axes1(S::Slice) = IdentityUnitRange(S.indices)
 axes(S::Slice{<:OneTo}) = (S.indices,)
@@ -366,7 +368,6 @@ getindex(S::Slice, i::StepRange{<:Integer}) = (@inline; @boundscheck checkbounds
 show(io::IO, r::Slice) = print(io, "Base.Slice(", r.indices, ")")
 iterate(S::Slice, s...) = iterate(S.indices, s...)
 
-
 """
     IdentityUnitRange(range::AbstractUnitRange)
 
@@ -378,6 +379,8 @@ struct IdentityUnitRange{T<:AbstractUnitRange} <: AbstractUnitRange{Int}
     indices::T
 end
 IdentityUnitRange(S::IdentityUnitRange) = S
+IdentityUnitRange{T}(S::IdentityUnitRange) where {T<:AbstractUnitRange} = IdentityUnitRange{T}(T(S.indices))
+
 # IdentityUnitRanges are offset and thus have offset axes, so they are their own axes
 axes(S::IdentityUnitRange) = (S,)
 axes1(S::IdentityUnitRange) = S
@@ -448,6 +451,8 @@ julia> linear[1,2]
 struct LinearIndices{N,R<:NTuple{N,AbstractUnitRange{Int}}} <: AbstractArray{Int,N}
     indices::R
 end
+convert(::Type{LinearIndices{N,R}}, inds::LinearIndices{N}) where {N,R<:NTuple{N,AbstractUnitRange{Int}}} =
+    LinearIndices{N,R}(convert(R, inds.indices))
 
 LinearIndices(::Tuple{}) = LinearIndices{0,typeof(())}(())
 LinearIndices(inds::NTuple{N,AbstractUnitRange{<:Integer}}) where {N} =
@@ -459,16 +464,17 @@ LinearIndices(A::Union{AbstractArray,SimpleVector}) = LinearIndices(axes(A))
 _convert2ind(i::Integer) = Base.OneTo(i)
 _convert2ind(ind::AbstractUnitRange) = first(ind):last(ind)
 
-promote_rule(::Type{LinearIndices{N,R1}}, ::Type{LinearIndices{N,R2}}) where {N,R1,R2} =
-    LinearIndices{N,indices_promote_type(R1,R2)}
-
 function indices_promote_type(::Type{Tuple{R1,Vararg{R1,N}}}, ::Type{Tuple{R2,Vararg{R2,N}}}) where {R1,R2,N}
     R = promote_type(R1, R2)
-    Tuple{R,Vararg{R,N}}
+    return Tuple{R, Vararg{R, N}}
 end
 
-convert(::Type{LinearIndices{N,R}}, inds::LinearIndices{N}) where {N,R} =
-    LinearIndices(convert(R, inds.indices))
+promote_rule(::Type{LinearIndices{N,R1}}, ::Type{LinearIndices{N,R2}}) where {N,R1,R2} =
+    LinearIndices{N,indices_promote_type(R1,R2)}
+promote_rule(a::Type{Slice{T1}}, b::Type{Slice{T2}}) where {T1,T2} =
+    el_same(promote_type(T1, T2), a, b)
+promote_rule(a::Type{IdentityUnitRange{T1}}, b::Type{IdentityUnitRange{T2}}) where {T1,T2} =
+    el_same(promote_type(T1, T2), a, b)
 
 # AbstractArray implementation
 IndexStyle(::Type{<:LinearIndices}) = IndexLinear()

base/promotion.jl

@@ -303,9 +303,9 @@ it for new types as appropriate.
 """
 function promote_rule end
 
-promote_rule(::Type{<:Any}, ::Type{<:Any}) = Bottom
+promote_rule(::Type, ::Type) = Bottom
 
-promote_result(::Type{<:Any},::Type{<:Any},::Type{T},::Type{S}) where {T,S} = (@inline; promote_type(T,S))
+promote_result(::Type,::Type,::Type{T},::Type{S}) where {T,S} = (@inline; promote_type(T,S))
 # If no promote_rule is defined, both directions give Bottom. In that
 # case use typejoin on the original types instead.
 promote_result(::Type{T},::Type{S},::Type{Bottom},::Type{Bottom}) where {T,S} = (@inline; typejoin(T, S))

base/range.jl

@@ -1263,13 +1263,17 @@ function -(r::LinRange)
     LinRange{typeof(start)}(start, -r.stop, length(r))
 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 # we assume a === b
 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)
 
+promote_result(::Type{<:AbstractArray}, ::Type{<:AbstractArray}, ::Type{T}, ::Type{S}) where {T,S} = (@inline; promote_type(T,S))
+promote_result(::Type{T}, ::Type{S}, ::Type{Bottom}, ::Type{Bottom}) where {T<:AbstractArray,S<:AbstractArray} = (@inline; promote_typejoin(T,S))
+# If no promote_rule is defined, both directions give Bottom. In that case use typejoin on the eltypes instead and give Array as the container.
+promote_result(::Type{<:AbstractArray{T,n}}, ::Type{<:AbstractArray{S,n}}, ::Type{Bottom}, ::Type{Bottom}) where {T,S,n} = (@inline; Array{promote_type(T,S),n})
+
 promote_rule(a::Type{UnitRange{T1}}, b::Type{UnitRange{T2}}) where {T1,T2} =
     el_same(promote_type(T1, T2), a, b)
 UnitRange{T}(r::UnitRange{T}) where {T<:Real} = r

test/bitarray.jl

@@ -98,6 +98,20 @@ 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...)
+    ex = (@test_throws ErrorException promote(ae, ones(sz...))).value
+    @test startswith(ex.msg, "promotion of types Bit")
+    ex = (@test_throws ErrorException promote(ae, falses(sz...))).value
+    @test startswith(ex.msg, "promotion of types Bit")
+end
+
+timesofar("promotions")
+
 @testset "utility functions" begin
     b1 = bitrand(v1)
     @test isequal(fill!(b1, true), trues(size(b1)))
@@ -1767,4 +1781,4 @@ end
         @test all(bitarray[rangeout, rangein] .== true)
         @test all(bitarray[rangein, rangeout] .== true)
     end
-end
+end

test/broadcast.jl

@@ -691,16 +691,19 @@ end
     @test a == [1 1; 2 2; 3 3]
 end
 
-@testset "scalar .=" begin
-    A = [[1,2,3],4:5,6]
+@testset "scalar .= and promotion" begin
+    A = [[1, 2, 3], 4:5, 6]
+    @test A isa Vector{Any}
     A[1] .= 0
-    @test A[1] == [0,0,0]
+    @test A[1] == [0, 0, 0]
     @test_throws Base.CanonicalIndexError A[2] .= 0
     @test_throws MethodError A[3] .= 0
-    A = [[1,2,3],4:5]
+    A = [[1, 2, 3], 4:5]
+    @test A isa Vector{Vector{Int}}
     A[1] .= 0
-    @test A[1] == [0,0,0]
-    @test_throws Base.CanonicalIndexError A[2] .= 0
+    A[2] .= 0
+    @test A[1] == [0, 0, 0]
+    @test A[2] == [0, 0]
 end
 
 # Issue #22180