Sort order is not stable in Accept class

[lincolnq]

    from werkzeug.datastructures import LanguageAccept
    from werkzeug.http import parse_accept_header

    a = parse_accept_header("en-US,fr-FR", LanguageAccept)
    assert a.best == "en-US"  # fails, it returns fr-FR

I expected the order to be preserved.

RFC 3282 describes desired behavior for Accept-Language: "If no Q values are given, the language-ranges are given in priority order, with the leftmost language-range being the most preferred language; this is an extension to the HTTP/1.1 rules, but matches current practice."

Looking at the source code, the Accept class is reverse-sorting the input list by specificity, then quality, then name; I think it should not sort by name and instead should preserve the given order.

[zgoda]

According to current standard which is RFC 7231 I'd rather expect a list in case of equal preference matches. There is a note there describing this exact case.

[pgjones]

See #1701 - I also think the parsed order should be preserved.