findmax does different things on Julia 1.6 and 1.7 with the same version of Compat

[ericphanson]

❯ julia-1.7 -q
julia> using Compat # v3.31.0

julia> findmax(identity, 5:9)
(9, 5)

julia> VERSION
v"1.7.0-beta2"

❯ julia-1.6 -q
julia> using Compat # v3.31.0

julia> findmax(identity, 5:9)
(9, 9)

julia> VERSION
v"1.6.1"

This is, of course, since the choice of what findmax does changed between when #738 was made and the 1.7-beta2 release, and in Compat, the definitions are gated around versions, so on 1.7 the real definition is let through, while on 1.6, the Compat definition is used.

But how do we fix this?

[fredrikekre]

Just update to match 1.7-beta?

[ericphanson]

Yeah, so Compat v4 can do that, and I guess v3 is just going to be inconsistent?

[fredrikekre]

Why not in v3? This is a bug in Compat.

[ericphanson]

Is it though? Changing the definition basically means any code using Compat for the findmax methods added in #738 will break (likely silently), and it was very explicit about what those methods did.

Compat tagged a release with those methods, Julia did not, so Julia can change them, but I don't think Compat can...

[fredrikekre]

I guess it was premature to tag the Compat release, but the job of Compat is to behave like Julia, and there have not been a Julia release with this behavior yet, so I would 100% call this a bug in Compat.