`Net::IMAP::SearchResult#to_sequence_set` raises `ArgumentError` for empty `Net::IMAP::SearchResult`

[Quintasan]

Hello,

I'm not sure if this is a bug (I think it is) but calling #to_sequence_set on empty Net::IMAP::SearchResult gives me ArgumentError:

strap(dev):011> s.imap.class
=> Net::IMAP
strap(dev):012> s.imap.uid_search(["ALL"])
=> []
strap(dev):013> s.imap.uid_search(["ALL"]).to_sequence_set
(strap):13:in '<main>': wrong number of arguments (given 0, expected 1+) (ArgumentError)

    caller: /home/quintasan/.local/share/mise/installs/ruby/4.0.2/lib/ruby/gems/4.0.0/gems/net-imap-0.6.3/lib/net/imap/search_result.rb:126
    |       def to_sequence_set; SequenceSet[*self] end
                                            ^^^^^^^
    callee: /home/quintasan/.local/share/mise/installs/ruby/4.0.2/lib/ruby/gems/4.0.0/gems/net-imap-0.6.3/lib/net/imap/sequence_set.rb:455
strap(dev):014> s.imap.uid_search(["ALL"]).class
=> Net::IMAP::SearchResult
strap(dev):015>

[nevans]

Yeah, that's a bug.

In the IMAP grammar, sequence-set isn't allowed to be empty. But Net::IMAP::SequenceSet can be empty... you just won't be able to use an empty sequence set as an argument to various IMAP commands.

Anyway, Net::IMAP::SequenceSet[*args] strictly enforces "valid only" (so not empty), but Net::IMAP::SequenceSet(arg) and Net::IMAP::SequenceSet.new(arg) are both fine with empty sets.

[nevans]

And, ESearchResult#to_sequence_set also returns SequenceSet.empty, so this should be consistent with that, too.

Unfortunately, I'd forgotten about SORT when I first wrote this. This still differs ESearchResult#to_sequence_set in that it doesn't preserve SORT order, but always returns a sorted set. I more explicitly documented that in #644, too.

I'd like to update it to preserve order. But that will require some extra effort to remain backward compatible. Sorting it actually was intentional, because I'd seen a couple of libraries mistakenly assuming that the server always returns SEARCH results in sorted order, and then incorrectly using the #first or #last values when they should've used #min or #max.

If we update the parser to store the result type (SEARCH or SORT) on the object, for example by making a SortResult class that's a subclass of SearchResult, we can vary the behavior based on that.