Make haskey(::@kwargs{item::Bool}, :item) constant-fold (#59320)

Resolves #59269.

~~Makes #59292 somewhat worse
by doubling-down on the same assumptions.~~

~~We should straighten out that issue properly, but I don't see any
reason not to get better inference in the mean time for the very common
`@Kwargs` case.~~ We are already relying on those assumptions in Base
(as that issue demonstrates), and @JeffBezanson says that this
functionality wasn't intended to be supported:
> I think the use case for it is picking not a subset, but alternate key
set, specifically linear or cartesian indices for arrays. [...] So go
ahead and add that haskey method

**edit:** now also resolves
#59292.

Author: topolarity

Compiler/test/inference.jl

@@ -6515,4 +6515,11 @@ end <: Bool
     Core.get_binding_type(m, n, xs...)
 end <: Type
 
+# issue #59269
+function haskey_inference_test()
+    kwargs = Core.compilerbarrier(:const, Base.pairs((; item = false)))
+    return haskey(kwargs, :item) ? nothing : Any[]
+end
+@inferred haskey_inference_test()
+
 end # module inference

base/essentials.jl

@@ -503,9 +503,9 @@ end
     Pairs{K, V, I, A}(data, itr) where {K, V, I, A} = $(Expr(:new, :(Pairs{K, V, I, A}), :(data isa A ? data : convert(A, data)), :(itr isa I ? itr : convert(I, itr))))
     Pairs{K, V}(data::A, itr::I) where {K, V, I, A} = $(Expr(:new, :(Pairs{K, V, I, A}), :data, :itr))
     Pairs{K}(data::A, itr::I) where {K, I, A} = $(Expr(:new, :(Pairs{K, eltype(A), I, A}), :data, :itr))
-    Pairs(data::A, itr::I) where  {I, A} = $(Expr(:new, :(Pairs{eltype(I), eltype(A), I, A}), :data, :itr))
+    Pairs(data::A, itr::I) where {I, A} = $(Expr(:new, :(Pairs{I !== Nothing ? eltype(I) : keytype(A), eltype(A), I, A}), :data, :itr))
 end
-pairs(::Type{NamedTuple}) = Pairs{Symbol, V, NTuple{N, Symbol}, NamedTuple{names, T}} where {V, N, names, T<:NTuple{N, Any}}
+pairs(::Type{NamedTuple}) = Pairs{Symbol, V, Nothing, NT} where {V, NT <: NamedTuple}
 
 """
     Base.Pairs(values, keys) <: AbstractDict{eltype(keys), eltype(values)}

base/iterators.jl

@@ -267,48 +267,48 @@ pairs(::IndexLinear,    A::AbstractArray) = Pairs(A, LinearIndices(A))
 # preserve indexing capabilities for known indexable types
 # faster than zip(keys(a), values(a)) for arrays
 pairs(tuple::Tuple) = Pairs{Int}(tuple, keys(tuple))
-pairs(nt::NamedTuple) = Pairs{Symbol}(nt, keys(nt))
+pairs(nt::NamedTuple) = Pairs{Symbol}(nt, nothing)
 pairs(v::Core.SimpleVector) = Pairs(v, LinearIndices(v))
 pairs(A::AbstractVector) = pairs(IndexLinear(), A)
 # pairs(v::Pairs) = v # listed for reference, but already defined from being an AbstractDict
 
 pairs(::IndexCartesian, A::AbstractArray) = Pairs(A, Base.CartesianIndices(axes(A)))
 pairs(A::AbstractArray)  = pairs(IndexCartesian(), A)
 
-length(v::Pairs) = length(getfield(v, :itr))
-axes(v::Pairs) = axes(getfield(v, :itr))
-size(v::Pairs) = size(getfield(v, :itr))
+length(v::Pairs) = length(keys(v))
+axes(v::Pairs) = axes(keys(v))
+size(v::Pairs) = size(keys(v))
 
 Base.@eval @propagate_inbounds function _pairs_elt(p::Pairs{K, V}, idx) where {K, V}
     return $(Expr(:new, :(Pair{K, V}), :idx, :(getfield(p, :data)[idx])))
 end
 
 @propagate_inbounds function iterate(p::Pairs{K, V}, state...) where {K, V}
-    x = iterate(getfield(p, :itr), state...)
+    x = iterate(keys(p), state...)
     x === nothing && return x
     idx, next = x
     return (_pairs_elt(p, idx), next)
 end
 
-@propagate_inbounds function iterate(r::Reverse{<:Pairs}, state=(reverse(getfield(r.itr, :itr)),))
+@propagate_inbounds function iterate(r::Reverse{<:Pairs}, state=(reverse(keys(r.itr)),))
     x = iterate(state...)
     x === nothing && return x
     idx, next = x
     return (_pairs_elt(r.itr, idx), (state[1], next))
 end
 
-@inline isdone(v::Pairs, state...) = isdone(getfield(v, :itr), state...)
+@inline isdone(v::Pairs, state...) = isdone(keys(v), state...)
 
 IteratorSize(::Type{<:Pairs{<:Any, <:Any, I}}) where {I} = IteratorSize(I)
 IteratorSize(::Type{<:Pairs{<:Any, <:Any, <:AbstractUnitRange, <:Tuple}}) = HasLength()
 
 function last(v::Pairs{K, V}) where {K, V}
-    idx = last(getfield(v, :itr))
+    idx = last(keys(v))
     return Pair{K, V}(idx, v[idx])
 end
 
-haskey(v::Pairs, key) = (key in getfield(v, :itr))
-keys(v::Pairs) = getfield(v, :itr)
+haskey(v::Pairs, key) = key in keys(v)
+keys(v::Pairs) = getfield(v, :itr) === nothing ? keys(getfield(v, :data)) : getfield(v, :itr)
 values(v::Pairs) = getfield(v, :data) # TODO: this should be a view of data subset by itr
 getindex(v::Pairs, key) = getfield(v, :data)[key]
 setindex!(v::Pairs, value, key) = (getfield(v, :data)[key] = value; v)

base/namedtuple.jl

@@ -343,7 +343,7 @@ merge(a::NamedTuple,     b::NamedTuple{()}) = a
 merge(a::NamedTuple{()}, b::NamedTuple{()}) = a
 merge(a::NamedTuple{()}, b::NamedTuple)     = b
 
-merge(a::NamedTuple, b::Iterators.Pairs{<:Any,<:Any,<:Any,<:NamedTuple}) = merge(a, getfield(b, :data))
+merge(a::NamedTuple, b::Iterators.Pairs{<:Any,<:Any,Nothing,<:NamedTuple}) = merge(a, getfield(b, :data))
 
 merge(a::NamedTuple, b::Iterators.Zip{<:Tuple{Any,Any}}) = merge(a, NamedTuple{Tuple(b.is[1])}(b.is[2]))
 
@@ -535,7 +535,7 @@ when it is printed in the stack trace view.
 
 ```julia
 julia> @Kwargs{init::Int} # the internal representation of keyword arguments
-Base.Pairs{Symbol, Int64, Tuple{Symbol}, @NamedTuple{init::Int64}}
+Base.Pairs{Symbol, Int64, Nothing, @NamedTuple{init::Int64}}
 
 julia> sum("julia"; init=1)
 ERROR: MethodError: no method matching +(::Char, ::Char)
@@ -578,7 +578,7 @@ Stacktrace:
 macro Kwargs(ex)
     return :(let
         NT = @NamedTuple $ex
-        Base.Pairs{keytype(NT),eltype(NT),typeof(NT.parameters[1]),NT}
+        Base.Pairs{keytype(NT),eltype(NT),Nothing,NT}
     end)
 end
 

base/show.jl

@@ -1116,6 +1116,8 @@ function show_type_name(io::IO, tn::Core.TypeName)
 end
 
 function maybe_kws_nt(x::DataType)
+    # manually-written version of
+    # x <: (Pairs{Symbol, eltype(NT), Nothing, NT} where NT <: NamedTuple)
     x.name === typename(Pairs) || return nothing
     length(x.parameters) == 4 || return nothing
     x.parameters[1] === Symbol || return nothing
@@ -1125,7 +1127,7 @@ function maybe_kws_nt(x::DataType)
         types isa DataType || return nothing
         x.parameters[2] === eltype(p4) || return nothing
         isa(syms, Tuple) || return nothing
-        x.parameters[3] === typeof(syms) || return nothing
+        x.parameters[3] === Nothing || return nothing
         return p4
     end
     return nothing
@@ -3219,7 +3221,7 @@ function Base.showarg(io::IO, r::Iterators.Pairs{<:Integer, <:Any, <:Any, T}, to
     print(io, "pairs(IndexLinear(), ::", T, ")")
 end
 
-function Base.showarg(io::IO, r::Iterators.Pairs{Symbol, <:Any, <:Any, T}, toplevel) where {T <: NamedTuple}
+function Base.showarg(io::IO, r::Iterators.Pairs{Symbol, <:Any, Nothing, T}, toplevel) where {T <: NamedTuple}
     print(io, "pairs(::NamedTuple)")
 end
 

test/namedtuple.jl

@@ -163,6 +163,10 @@ end
 @test merge(NamedTuple(), [:a=>1, :b=>2, :c=>3, :a=>4, :c=>5]) == (a=4, b=2, c=5)
 @test merge((c=0, z=1), [:a=>1, :b=>2, :c=>3, :a=>4, :c=>5]) == (c=5, z=1, a=4, b=2)
 
+# https://github.com/JuliaLang/julia/issues/59292
+@test merge((; a = 1), Base.Pairs((; b = 2, c = 3), (:b,))) == (a = 1, b = 2)
+@test merge((; a = 1), Base.pairs((; b = 2, c = 3))) == (a = 1, b = 2, c = 3)
+
 @test keys((a=1, b=2, c=3)) == (:a, :b, :c)
 @test keys(NamedTuple()) == ()
 @test keys((a=1,)) == (:a,)

test/show.jl

@@ -1450,7 +1450,7 @@ test_repr("(:).a")
 @test repr(@NamedTuple{var"#"::Int64}) == "@NamedTuple{var\"#\"::Int64}"
 
 # Test general printing of `Base.Pairs` (it should not use the `@Kwargs` macro syntax)
-@test repr(@Kwargs{init::Int}) == "Base.Pairs{Symbol, $Int, Tuple{Symbol}, @NamedTuple{init::$Int}}"
+@test repr(@Kwargs{init::Int}) == "Base.Pairs{Symbol, $Int, Nothing, @NamedTuple{init::$Int}}"
 
 @testset "issue #42931" begin
     @test repr(NTuple{4, :A}) == "Tuple{:A, :A, :A, :A}"