Reading the documentation about conversion and promotion of 0.6.2, the isnan line looked weird:

function convert(::Type{Rational{T}}, x::AbstractFloat, tol::Real) where T<:Integer
    if isnan(x); return zero(T)//zero(T); end

The issue is multiple:

• in the actual source convert has been changed to rationalize. The doc could be updated, for clarity.
• Trying that in julia 0.6.2 yields an error message that could be puzzling before looking at the source.

julia> rationalize(Int64, NaN, 1e-16)
ERROR: ArgumentError: invalid rational: zero(Int64)//zero(Int64)
Stacktrace:
 [1] Rational{Int64}(::Int64, ::Int64) at ./rational.jl:13
 [2] rationalize(::Type{Int64}, ::Float64, ::Float64) at ./rational.jl:131

What about replacing zero(T)//zero(T) with something like throw(ArgumentError("received NaN, not allowed for integer-related types") ?

Here is the corresponding line in the repo:

This is not #25702.