Errors from findfirst(..., ::StepRange{Date,Year})

[mcabbott]

This worked on Julia 1.0 and 1.1, but fails from 1.2 to 1.5:

using Dates
ys = Date(1852):Year(4):Date(1940)
y0 = ys[21+1]
findfirst(isequal(y0), ys) # MethodError: Cannot `convert` an object of type Day to an object of type Year

findfirst(isequal(y0), collect(ys)) # fine

This seems like a bug to me, as the range ought to be treated the same way as the collected array.

The method, which I think was added in #30778, is here:

julia/base/array.jl

Line 1794 in 9466232

function findfirst(p::Union{Fix2{typeof(isequal),T},Fix2{typeof(==),T}}, r::StepRange{T,S}) where {T,S}

It works fine for some dates, like DateTime(2017):Second(1):DateTime(2020) mentioned in the PR. But every second is the same length, while years vary.

[mcabbott]

Notice that Base.RangeStepStyle(ys) == Base.RangeStepIrregular(). Perhaps this is the flag which #30778 ought to check?