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RFC: allow Tuple{Union{}}, returning Union{} #53452

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RFC: allow Tuple{Union{}}, returning Union{} #53452

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1 change: 1 addition & 0 deletions base/promotion.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -496,6 +496,7 @@ else
_return_type(@nospecialize(f), @nospecialize(t)) = Any
end

# return Tuple{tt...} if the all given elements may have instances, otherwise return Union{} if any cannot have instances
function TupleOrBottom(tt...)
any(p -> p === Union{}, tt) && return Union{}
return Tuple{tt...}
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2 changes: 1 addition & 1 deletion src/jltypes.c
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Expand Up @@ -1927,7 +1927,7 @@ static jl_value_t *inst_datatype_inner(jl_datatype_t *dt, jl_svec_t *p, jl_value
}
}
if (pi == jl_bottom_type)
jl_errorf("Tuple field type cannot be Union{}");
return jl_bottom_type;
if (cacheable && !jl_is_concrete_type(pi))
cacheable = 0;
}
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6 changes: 6 additions & 0 deletions test/compiler/codegen.jl
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Expand Up @@ -652,6 +652,7 @@ end
# issue #41157
f41157(a, b) = a[1] = b[1]
@test_throws BoundsError f41157(Tuple{Int}[], (NTuple{N,Union{}} where N)[])
@test_throws BoundsError f41157(Tuple{Int}[], Tuple{Union{}}[])

# issue #41096
struct Modulate41096{M<:Union{Function, Val{true}, Val{false}}, id}
Expand Down Expand Up @@ -788,6 +789,11 @@ f_isa_type(@nospecialize(x)) = isa(x, Type)
f47247(a::Ref{Int}, b::Nothing) = setfield!(a, :x, b)
@test_throws TypeError f47247(Ref(5), nothing)

@testset "regression in generic_bitcast: should support Union{} values" begin
f(x) = Core.bitcast(UInt, Core.compilerbarrier(:type, x)::Int)
@test occursin("unreachable", get_llvm(f, Tuple{UInt}))
end

f48085(@nospecialize x...) = length(x)
@test Core.Compiler.get_compileable_sig(which(f48085, (Vararg{Any},)), Tuple{typeof(f48085), Vararg{Int}}, Core.svec()) === nothing
@test Core.Compiler.get_compileable_sig(which(f48085, (Vararg{Any},)), Tuple{typeof(f48085), Int, Vararg{Int}}, Core.svec()) === Tuple{typeof(f48085), Any, Vararg{Any}}
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2 changes: 1 addition & 1 deletion test/compiler/inference.jl
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Expand Up @@ -1096,7 +1096,7 @@ end
g21771(T) = T
f21771(::Val{U}) where {U} = Tuple{g21771(U)}
@test @inferred(f21771(Val{Int}())) === Tuple{Int}
@test_throws ErrorException @inferred(f21771(Val{Union{}}()))
@test @inferred(f21771(Val{Union{}}())) === Union{}
@test @inferred(f21771(Val{Integer}())) === Tuple{Integer}

# PR #28284, check that constants propagate through calls to new
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13 changes: 4 additions & 9 deletions test/subtype.jl
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Expand Up @@ -596,7 +596,7 @@ function test_old()
end

const easy_menagerie =
Any[Any, Int, Int8, Integer, Real,
Any[Bottom, Any, Int, Int8, Integer, Real,
Array{Int,1}, AbstractArray{Int,1},
Tuple{Int,Vararg{Integer}}, Tuple{Integer,Vararg{Int}}, Tuple{},
Union{Int,Int8},
Expand Down Expand Up @@ -635,10 +635,7 @@ end

add_variants!(easy_menagerie)
add_variants!(hard_menagerie)
push!(easy_menagerie, Bottom)
push!(easy_menagerie, Ref{Bottom})
push!(easy_menagerie, @UnionAll N NTuple{N,Bottom})
push!(easy_menagerie, @UnionAll S<:Bottom Ref{S})

const menagerie = [easy_menagerie; hard_menagerie]

Expand Down Expand Up @@ -685,11 +682,9 @@ function test_properties()
@test isequal_type(T, S) == isequal_type(Ref{T}, Ref{S})

# covariance
if T !== Bottom && S !== Bottom
@test issubTS == issub(Tuple{T}, Tuple{S})
@test issubTS == issub(Tuple{Vararg{T}}, Tuple{Vararg{S}})
@test issubTS == issub(Tuple{T}, Tuple{Vararg{S}})
end
@test issubTS == issub(Tuple{T}, Tuple{S})
@test issubTS == issub(Tuple{Vararg{T}}, Tuple{Vararg{S}})
@test issubTS == issub(Tuple{T}, Tuple{Vararg{S}})

# pseudo-contravariance
@test issubTS == issub(¬S, ¬T)
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4 changes: 2 additions & 2 deletions test/tuple.jl
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Expand Up @@ -803,8 +803,8 @@ namedtup = (;a=1, b=2, c=3)
# some basic equivalence handling tests for Union{} appearing in Tuple Vararg parameters
@test Tuple{} <: Tuple{Vararg{Union{}}}
@test Tuple{Int} <: Tuple{Int, Vararg{Union{}}}
@test_throws ErrorException("Tuple field type cannot be Union{}") Tuple{Int, Vararg{Union{},1}}
@test_throws ErrorException("Tuple field type cannot be Union{}") Tuple{Vararg{Union{},1}}
@test Tuple{Int, Vararg{Union{},1}} === Union{}
@test Tuple{Vararg{Union{},1}} === Union{}
@test Tuple{} <: Tuple{Vararg{Union{},N}} where N
@test !(Tuple{} >: Tuple{Vararg{Union{},N}} where N)

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Suggested change
@testset "#52385" begin
eagerzip() = error()
function eagerzip(args::AbstractArray...)
allequal(axes.(args)) || throw(DimensionMismatch())
Base.require_one_based_indexing(args...)
res = similar(first(args), Tuple{eltype.(args)...})
for i in eachindex(args...)
res[i] = getindex.(args, i)
end
res
end
@test isempty(eagerzip(Int[], []))
@test eltype(eagerzip(Int[], [])) === Tuple{Int64, Any}
@test isempty(eagerzip(Union{}[], []))
@test eltype(eagerzip(Union{}[], [])) === Union{}
end

Seems worthwhile to grab @LilithHafner's test case from #52385 (comment)

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