Re: package dependencies

[Leo Famulari <leo@famulari.name>]

On Mon, Dec 14, 2015 at 10:28:57AM +0100, Pjotr Prins wrote:
> The problem with the main text is that it is written from the view
> point of technology. I would like something more human that reads like
> an instruction for packagers. Be great if we had something useful
> there, otherwise questions will be asked again and again :). And I
> will have to point to guix-notes every time.

It's true, an extremely technical explanation will be completely useful
and accurate and ... it won't help many of the readers who actually need
help. It is very easy to package simple programs for Guix. But I have
found that as soon as the program deviates from the Autotools or
setup.py script at all, you really need some domain-specific technical
knowledge to finish the package. I have personally learned a lot about
many subjects while packaging for Guix.

See the recent ML thread about packaging 'sent'.

> 
> I agree my version is less accurate, but it acts like a summing up and
> (actually) is precisely the way I look at these statements. We can
> have both. I am not saying we should replace your section.

I think we are all loath to include inaccuracies in the manual. But on
the other hand, I think we need to find a way to summarize the
distinction that is close to what Pjotr is proposing.

Some of us have an understanding of the subject that is directly based
on the Guix / Nix source code. The rest of us have learned by
trial-and-error and rough heuristics like Pjotr's summary (hopefully we
will all 'use the source' eventually ;) .

The difficult thing is explaining it in a way that "sets up" the reader
for further learning. You must be accurate, but you must not be too
verbose, because when you are banging your head against the wall, it is
difficult to read a long text.

The other day, this helpful jewel was shared by mark_weaver on #guix [0]:
fhmgufs: the distinction between build and runtime dependencies is
determined by scanning the outputs of the build for references to
/gnu/store/....

Learning the mechanism made it clear to me. This is why Python inputs
must be propagated: there is nowhere in the main Python program to link
to dependencies in the store, so the inputs must be propagated onto
PYTHONPATH. I already understood the difference between 'native-inputs'
and 'inputs', and this doesn't really get to the heart of the
difference, but it does draw a line between them.

I propose we adapt this statement for use in the manual (assuming that
is accurate).

If there is no updated patch in a few hours, I will write one, but I
can't do it at the moment.

[0]
https://gnunet.org/bot/log/guix/2015-12-09

PS— I can't follow the "flow" of this conversation because some people
are replying in-line while others are top-posting. Please, let's pick
one (I vote for in-line).

> 
> Anyway, maybe I am the only one seeing it like this.
> 
> Pj.
> 
> On Mon, Dec 14, 2015 at 09:58:19AM +0100, Ludovic Courtès wrote:
> > Pjotr Prins <pjotr.public12@thebird.nl> skribis:
> > 
> > > Thanks Ludo. I still think it could be made a little clearer from the packager's 
> > > perspective. How about concluding it with something like:
> > >
> > > In short, to create a package, by default you should use 'inputs' for
> > > dependencies. Use 'native-inputs' for tools used at build-time, but
> > > not at runtime and use propagated-inputs when the other two do not
> > > suffice.
> > 
> > This is certainly shorter, but the problem I have with that is that it
> > does not accurately explain what’s going on.  The current text is
> > admittedly more verbose, but I think it is more accurate.
> > 
> > Hope that makes sense.
> > 
> > Ludo’.
> > 
> 
> -- 
>