dispatch failure depending on order of imports

[stevengj]

I encountered an interesting situation in JuliaMath/QuadGK.jl#63. If I run the following code:

using Unitful, QuadGK
f(t) = 1.0u"J"
quadgk(f, 0.0u"s", 10.0u"s")

in Julia 1.8.2 (x86_64-apple-darwin21.4.0, QuadGK 2.6.0, and Unitful v1.12.2) then it works fine, but if I change the order of the using statements:

using QuadGK, Unitful
f(t) = 1.0u"J"
quadgk(f, 0.0u"s", 10.0u"s")

then it gives a bizarre MethodError:

julia> quadgk(f, 0.0u"s", 10.0u"s")
ERROR: MethodError: no method matching Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}(::Int64)
The applicable method may be too new: running in world age 32427, while current world is 32430.
Closest candidates are:
  Quantity{T, D, U}(::Number) where {T, D, U} at ~/.julia/packages/Unitful/fbiNW/src/types.jl:151 (method too new to be called from this world context.)
  (::Type{T})(::T) where T<:Number at boot.jl:772
  (::Type{T})(::AbstractChar) where T<:Union{AbstractChar, Number} at char.jl:50
  ...
Stacktrace:
  [1] convert(#unused#::Type{Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}}, x::Int64)
    @ Base ./number.jl:7
  [2] one(#unused#::Type{Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}})
    @ Base ./number.jl:334
  [3] #s14#1
    @ ~/.julia/packages/QuadGK/kf0xA/src/gausskronrod.jl:260 [inlined]
  [4] var"#s14#1"(T::Any, ::Any, #unused#::Any, n::Any)
    @ QuadGK ./none:0
  [5] (::Core.GeneratedFunctionStub)(::Any, ::Vararg{Any})
    @ Core ./boot.jl:582
  [6] do_quadgk(f::typeof(f), s::Tuple{Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}, Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}}, n::Int64, atol::Nothing, rtol::Nothing, maxevals::Int64, nrm::typeof(LinearAlgebra.norm), segbuf::Nothing)
    @ QuadGK ~/.julia/packages/QuadGK/kf0xA/src/adapt.jl:7
  [7] #28
    @ ~/.julia/packages/QuadGK/kf0xA/src/adapt.jl:186 [inlined]
  [8] handle_infinities(workfunc::QuadGK.var"#28#29"{Nothing, Nothing, Int64, Int64, typeof(LinearAlgebra.norm), Nothing}, f::typeof(f), s::Tuple{Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}, Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}})
    @ QuadGK ~/.julia/packages/QuadGK/kf0xA/src/adapt.jl:115
  [9] quadgk(::Function, ::Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}, ::Vararg{Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}}; atol::Nothing, rtol::Nothing, maxevals::Int64, order::Int64, norm::Function, segbuf::Nothing)
    @ QuadGK ~/.julia/packages/QuadGK/kf0xA/src/adapt.jl:185
 [10] quadgk(::Function, ::Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}, ::Vararg{Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}})
    @ QuadGK ~/.julia/packages/QuadGK/kf0xA/src/adapt.jl:183
 [11] top-level scope
    @ REPL[3]:2

And note from the stacktrace that it is calling this fallback method of one(T), which should not be the case. It should be calling the one method in Unitful.jl:

julia> T = typeof(0.0u"s")
Quantity{Float64, 𝐓, Unitful.FreeUnits{(s,), 𝐓, nothing}}

julia> one(T)
1.0

julia> @which one(T)
one(x::Type{<:Unitful.AbstractQuantity}) in Unitful at /Users/stevenj/.julia/packages/Unitful/fbiNW/src/quantities.jl:422

Seems like there is some kind of stale code where it is calling one from an old version (an old "world age") of the method table?

[stevengj]

@mikeingold reproduced in Julia 1.9.0-beta2 (JuliaMath/QuadGK.jl#63 (comment)).

[vtjnash]

This seems like probably a design error in one of the package, since we see it getting called from an @generated function, but those are not supposed to be written to have any dependency on world ages. It looks like QuadGK/kf0xA/src/gausskronrod.jl:260 is being blamed there for calling one, which is not a valid function to call from a function generator since it is 'generic' (expected to be overloaded)

[stevengj]

Got it, closing this and will fix it in QuadGK.