[darcs-users] Assumption Check (Patch Ordering)

[Max Battcher]

On 2/27/06, Juliusz Chroboczek <Juliusz.Chroboczek at pps.jussieu.fr> wrote:
> > Any good suggestions, then, on how to approach handling the ordering
> > of patches without calling darcs every time?
>
> Use repository ordering, but make sure that you regenerate your
> database every time somebody calls an unsafe darcs operation.
>
> Unsafe operations are optimize, repair, unpull and unrecord (am I
> missing any?).

Right, that makes sense and it should be easy enough to run the
marshalling posthook on any unsafe operations and/or disable them for
such repositories (this is meant for repo-browsing like darcsweb, so
having a defaults with the unsafe operations disabled would be a
useful thing to have in this project's documentation/examples).

Right now I'm building this in an onion-approach (low level to high
level), and I've got the general patch view, which is generally
date-ordered (because the dates are an inherent facet of the patch). 
This corresponds fine with the repos that I'm working with and for
basic repositories (smallish ones with mostly logical patches) this
appears fine.

If I'm going to introduce repo-ordering its going to be at the next
"level" in the abstraction onion, as I don't think it makes sense for
a patch to know its repo order (particularly if the same patch table
stores patches for multiple repositories).  Now I'm just trying to
debate what that next level should be and the best way to go about
representing it in the database.

The obvious next level up (in terms of a user's view) is the Tag (and
then Repo/Branch has a collection of Tags, plus a repo-specific "Head"
tag, plus a collection of Files (and then Project has a collection of
Repos/Branches, etc)).  The problem I'm coming to, however, is I'm
trying to figure out how best to model Tags in the database.  In
particular, I'm having a hard time of figuring out how to get
"idempotent"  tag information from darcs (ie, if two repos have the
same tag I shouldn't have to reverify that tag's patch/tag dependency
order).  For example, if I'm reading through ``darcs changes -s
--xml-output`` and the patch's name, date, author, hash, invert match
and existing patch in the database I can reasonably assume that the
patch in the database is the same patch, and that I don't need to
remarshal the patch summary (or even patch diff when I get around to
that...).  But, how do I get *the* patch dependency for a Tag? 
Naively, I could assume all of the patches "below" a Tag in the
changes list, but its already been proven previously in the thread
that that might not necessarily be the case.  Also, I don't see any
way to determine if a patch is a tag other than for regexing for
"^TAG" in the change list.

Basically, it seems that Tags are "second-class patches" to ``darcs
changes``, which is great for abstraction (it is useful seeing the Tag
patches in the Patch Log), but seems to be tough for seeking
tag-specific information.  Also, why doesn't the --xml-output
<summary> tags have some sort of <tagged> change, like it has
adds/modifies/removes?  (This would be particularly useful should
there come a day should darcs move to allowing Tags within larger
logical patches, which I have seen debated previously.)

Time for ``darcs query tags``?

--
--Max Battcher--
http://www.worldmaker.net/
All progress is based upon a universal innate desire on the part of
every organism to live beyond its income. --Samuel Butler