Le Sat, 31 Oct 2020 18:30:07 +0100,
Ludovic Courtès <ludo@gnu.org> a écrit :

> Hi Julien,
> 
> Julien Lepiller <julien@lepiller.eu> skribis:
> 
> > %load-path lists ~/.config/guix/current before individual channels.
> >  We use canonicalize-path to get the store path for channel
> > packages.
> >
> > * guix/describe.scm (package-provenance): Use canonicalize-path.
> 
> [...]
> 
> >       (let ((file (if (string-prefix? "/" file)
> >                       file
> > -                     (search-path %load-path file))))
> > +                     (canonicalize-path (search-path %load-path
> > file)))))
> 
> Could you explain what problem it solves, perhaps with a simple
> reproducer?

Thanks for the answer!

Maybe this is only an issue in guix repl, but when looking for the
provenance of a package that's defined in a channel, I always get `#f`:

guix repl
,use (guix describe)
,use (gnu packages gettext)
,use (my channel packages)
(package-provenance po4a) -> I get the guix channel
(package-provenance my-package) -> I get #f

To me, this is caused by the search-path returning a path in
~/.config/guix/current instead of /gnu/store as it does for po4a:

(search-path %load-path "gnu/packages/gettext.scm") -> /gnu/store...
(search-path %load-path "my/channel/packages.scm") -> /home/...

The reason why I use canonicalize-path here is because doing so, I get
a path in the store, that is the content of the channel, so the
procedure can return that channel as the provenance for the package.
Unfortunately, %load-path seems to be weirdly set when using
pre-inst-env, so I'm not sure how to test (channel modules are not even
found).

> 
> ‘search-path’ can return #f (there’s a test right below), so this
> should probably be: (and=> (search-path …) canonicalize-path).
> 
> As a rule of thumb, I think twice before calling ‘canonicalize-path’
> because (1) it’s expensive (lots of stat(2) calls), and (2) it can
> have undesirable effects on the UI (messages mention a file name
> other than the one the user typed) and elsewhere (on logic that looks
> at what the file name looks like).

I think the result of canonicalize-path is only used internally in that
function to find the channel a package comes from, but is never used
outside of this function (it's not returned).

> 
> Maybe it’s OK here, but I mention this for completeness.
> 
> Thanks,
> Ludo’.

Attached is an updated patch.