[darcs-users] Getting a full diff for pulled patches

[Alexander Staubo]

On 7/25/07, David Roundy <droundy at darcs.net> wrote:
> Locally cloning is pretty fast (should be blinding [...]

Hm, I don't think so:

$ time darcs get --partial trunk trunk.test
Copying patch 2153 of 2153... done.
Applying patch 2152 of 2152... done.
Finished getting.

real    1m12.621s
user    0m20.628s
sys     0m15.593s

This is a small repo -- 3,500 files or around 24MB in total (excluding
_darcs, which has 5,600 files, or 64MB). Perhaps this operation is
fairly quick with recently-checkpointed repos, but I can't count on
this being the case; the operation I am implementing cannot take more
than a second or so.

Actually, my question is similar to the FAQ (asked just recently on
this list) about how to retrieve a specific version of a file. Given a
patch -- specifically, one that can be pulled from a remote repository
but has not been applied yet -- I want to obtain the file it can be
applied to.

>From what I can tell, I can accomplish this the following way: (1)
Read the current pristine from _darcs/pristine. (2) Run "pull
--dry-run --verbose --matches=...". (3) For each patch minus the patch
I actually want, take each hunk and apply it to the file. Hunks are
simple enough to parse that I can apply them directly without going
through Darcs.

The end result, as far as I can see, should be the ancestor of the
patch I want. I think I can be able to detect conflicts this way, too.

The actual case I want to solve is when pulling a bunch of patches
from another repo. I want to display each patch individually to the
user, showing the original file before it was changed. To do this, I
use the algorithm above, but because I'm processing multiple patches
against multiple files, I maintain a separate working files (one per
file per patch) internally that I apply the hunks to.

The process for push is similar, but I need to use "darcs changes"
instead to build up the original file; in fact, I guess I can skip the
read-the-pristine-file step and simply use the --to-match argument to
get the entire change history.

> > Absolutely. Darcs does not supply this dependency information,
> > unfortunately. Some trickery with "pull --no-deps" might be used to
> > detect dependencies.
>
> You can do simple things by using 'w' (or 'j') instead of 'n' if you want
> to pull a patch only if it's required by another that you say 'y' to later.
> In fact, if you choose, you can extract (almost?) all the patch
> dependencies from a single call to pull, by judicious use of 'y', 'n', 'w',
> 'j' and 'k'.  The only catch is that the dependencies of the last patch are
> tricky to get, since if you say 'y' to that patch, darcs immediately starts
> the actual pull.

I take it you did not read my original message. :) Darcs is actually
being invoked non-interactively here, by an application; the app
drives Darcs, parsing its output. I will not attempt to communicate
with the interactive Darcs prompt, I think -- it will be too brittle.

I think that the only reliable, programmatic way of detecting
dependencies is to run "darcs pull --dry-run --matches=..." on each
individual patch name. Of course, this will not let me build an exact
graph of dependencies, but I don't need that.

The problem with this approach is that it is going to be very slow
with remote repositories.

Alexander.