question about revset usage

[Faheem Mitha]

On Mon, 22 Sep 2014, Mads Kiilerich wrote:

> On 09/21/2014 10:45 AM, Faheem Mitha wrote:
>> If I use revsets as follows:
>> 
>> faheem at orwell:/usr/local/src/mercurial/hg$  hg log -r 
>> 'author(mpm at selenic.com)'
>> 
>> The order of the csets is reversed - the oldest csets are at the top, 
>> unlike the normal result of `hg log` where the newest csets are at the top. 
>> I.e.
>> 
>> faheem at orwell:/usr/local/src/mercurial/hg$  hg log -l1 -r 
>> 'author(mpm at selenic.com)'
>> changeset:   0:9117c6561b0b
>> user:        mpm at selenic.com
>> date:        Tue May 03 13:16:10 2005 -0800
>> summary:     Add back links from file revisions to changeset revisions
>> 
>> I rarely use revsets, but in any case, I've not noticed this behavior 
>> before, nor could I find any documentation about it. I also can't think of 
>> any good reason for this behavior. If this is correct behavior, and if I am 
>> not missing something obvious, I suggest it be documented somewhere.
>
> The unsorted order of revsets is not documented and can thus be considered 
> undefined and can thus not be wrong. If you want a special order, use sort().
>
> One reason to have it that way is that different predicates most efficiently 
> will yield results in different orders. For example, everything involving 
> unpacking of revlogs is most efficiently done with increasing rev numbers, 
> while ancestors obviously yield descreasing rev numbers.
>
> I agree that it would be nice if everything used the same order (decreasing!) 
> unless another sorting was requested but I am afraid that it would break a 
> lot of existing revsets out there so it might not be feasible to change it 
> even though it is undocumented and somewhat surprising behaviour. Documenting 
> it beyond the fact that it is undefined might not be feasible.

> (In Kallithea we take care to always show revisions in the "right" order ... 
> also because graphs become very confusing if shown upside down.)

Thank you for the clarification. I think this is worth documenting that 
the order of csets is undefined. It appears to be currently undocumented. 
What do you think?

                                                     Regards, Faheem Mitha