Re: Recent change in 'guix package --search-paths' behavior?

[Chris Marusich <cmmarusich@gmail.com>]

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Hi Ludo,

ludo@gnu.org (Ludovic Courtès) writes:

> Chris Marusich <cmmarusich@gmail.com> skribis:
>
>> Hi,
>>
>> The manual says ((guix) Invoking guix package):
>>
>>      This option can also be used to compute the _combined_ search paths
>>      of several profiles.  Consider this example:
>>
>>           $ guix package -p foo -i guile
>>           $ guix package -p bar -i guile-json
>>           $ guix package -p foo -p bar --search-paths
>>
>>      The last command above reports about the ‘GUILE_LOAD_PATH’
>>      variable, even though, taken individually, neither ‘foo’ nor ‘bar’
>>      would lead to that recommendation.
>
> [...]
>
>> Is the documentation wrong, or is this a regression?
>
> Try with “guile2.2-json” instead of “guile-json”.
>
> Ludo’.

As usual, you're right!  :-)  That worked:

--8<---------------cut here---------------start------------->8---
[0] marusich@garuda:/tmp
$ guix package -p foo -i guile
The following package will be installed:
   guile	2.2.2	/gnu/store/5zx29y44nrqj0s8h3jlvlj82k8hj4dxs-guile-2.2.2

1 package in profile
The following environment variable definitions may be needed:
   export PATH="foo/bin${PATH:+:}$PATH"
[0] marusich@garuda:/tmp
$ guix package -p bar -i guile2.2-json
The following package will be installed:
   guile2.2-json	0.6.0	/gnu/store/a7hrfb8p7syai31rxhrcrmlq81kjcs5v-guile2.2-json-0.6.0

1 package in profile
[0] marusich@garuda:/tmp
$ guix package -p foo -p bar --search-paths
export PATH="foo/bin"
export GUILE_LOAD_PATH="bar/share/guile/site/2.2"
export GUILE_LOAD_COMPILED_PATH="bar/share/guile/site/2.2"
[0] marusich@garuda:/tmp
$ 
--8<---------------cut here---------------end--------------->8---

Why does 'guix' resolve to guile@2.2.2, but 'guile-json' resolves to
guile-json@0.6.0?  Is it because, as mentioned in the comments in
procedure 'find-newest-available-packages' in gnu/packages.scm, "the
preferred package is whichever one was found last by 'fold-packages'"?

I've attached a patch for the documentation which might help clarify
this for anyone who has the same question in the future.  What do you
think?  Too much detail for an edge case, or a useful footnote?

-- 
Chris

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From 1b108931e88374a1835fb90dd6b0ebf715f3a267 Mon Sep 17 00:00:00 2001
From: Chris Marusich <cmmarusich@gmail.com>
Date: Wed, 10 May 2017 23:05:31 -0700
Subject: [PATCH] doc: Clarify 'guix package --search-paths' example.

* doc/guix.texi (Invoking guix package): Explain why, in some cases, a user
  who runs the example code for 'guix package --search-paths' might see
  different results than what is written in the manual.
---
 doc/guix.texi | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index 9b2fe3fdb..57f9f7863 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -1802,7 +1802,13 @@ $ guix package -p foo -p bar --search-paths
 
 The last command above reports about the @code{GUILE_LOAD_PATH}
 variable, even though, taken individually, neither @file{foo} nor
-@file{bar} would lead to that recommendation.
+@file{bar} would lead to that recommendation@footnote{This example will
+only work as written if @code{guile-json} was built for the same major
+version of Guile that @code{guile} refers to (e.g., 2.x.x).  If that is
+not the case, then this command will @emph{not} report about
+@code{GUILE_LOAD_PATH} because the two packages were built for different
+major versions of Guile.  @xref{Invoking guix package}, for more
+information about how to precisely specify packages.}.
 
 
 @item --profile=@var{profile}
-- 
2.12.2


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