List.sortBy produces different order between Chromium/Chrome and Firefox

[wknapik]

Edit: @evancz moved this gist directly into the issue.

2 6 3 4 5 1 7 10 9 11 8  -- Chromium/Chrome 66.0.3359.139 and 66.0.3359.170
2 6 1 3 4 5 7 9 10 11 8  -- Firefox 59.0.2 and 60.0

Tested on Linux.

import Html exposing (div, text)
import List
import Tuple

main =
   Html.beginnerProgram { model = [], view = view, update = (\_ -> \x -> x) }

view _ =
   div [] <| List.map (div [] << List.singleton << text << Tuple.first) (List.sortBy Tuple.second tuples)

tuples =
   [ ( "1", "foo" )
   , ( "2", "bar" )
   , ( "3", "foo" )
   , ( "4", "foo" )
   , ( "5", "foo" )
   , ( "6", "baz" )
   , ( "7", "foo" )
   , ( "8", "quux" )
   , ( "9", "foo" )
   , ( "10", "foo" )
   , ( "11", "foo" )
   ]

Thanks to @showell for helping out with this on slack.

[eriktim]

I am running into the same issue with Node 10 vs 11 (running elm-test on Travis).
For Chrome it seems to be fixed since v70: https://mobile.twitter.com/mathias/status/1036626116654637057?s=19. The latest Chrome indeed shows the correct result for me (like Firefox).

[eriktim]

To add some background: Elm's List.sortBy uses Array.prototype.sort under the hood. That sorting function is not guaranteed to be stable, i.e. the original order is not guaranteed for equally sorted values.

[robinheghan]

As of EC2020, Array.prototype.sort must be stable. See here: https://tc39.github.io/ecma262/#sec-array.prototype.sort

So this will come to all evergreen JS environments in time.