Re: Search paths vs. environment variables that designate a single file

[宋文武 <iyzsong@gmail.com>]

Ludovic Courtès <ludo@gnu.org> writes:

> 宋文武 <iyzsong@gmail.com> skribis:
>
>> Ludovic Courtès <ludo@gnu.org> writes:
>>
>>> With commit dbc31ab, it is now possible to do things like:
>>>
>>>   eval `guix package --search-paths=suffix`
>>>
>>> to augment the search path environment variables instead of overriding
>>> them.
>> Doesn't the KIND field belong to 'search-path-specification'?
>> Some variables are exact (GDK_PIXBUF_MODULE_FILE, GTK_DATA_PREFIX, etc.)
>> by definition.
>
> What do you mean?
>
> Here ‘exact’ means:
>
>   export PATH=/foo
>
> whereas ‘prefix’ means:
>
>   export PATH=/foo:$PATH
>
> This is not a property of the ‘PATH’ variable, but rather a choice that
> the user can make.
OK.
>
> What makes ‘GDK_PIXBUF_MODULE_FILE’ particular?  From the name I’m
> guessing it is *not* a search path, but rather is meant to specify a
> single file.  This is not what ‘search-path-specification’ is for, at
> least in its current form.
Yes, that's right.
>
>> I'd like to add 'GTK_DATA_PREFIX' and 'GTK_EXE_PREFIX' to gtk+
>> as 'exact' native-search-paths.
>> They generate value to profile as:
>>   - /run/current-system/profile, if you have installed xfce system wide.
>>   - ~/.guix-profile, if you installed xfce into user's profile.
>> So, the GTK+ themes will work out-of-box.
>
> Likewise, it seems that these are not search paths.
>
> This is not the first time there’s this temptation to use
> ‘search-path-specification’ for things that are not search paths.
> Clearly there seems to be a need for a similar mechanism, but we need to
> find a way for formalize it.
Hm, currently the 'search-paths' is the only way for a specified package
to populate environment variables into profile (and builder).  I tend to
think 'search-paths' are designed for build, but they are unually useful
(and same) for profile too.
>
> One way might be to augment ‘search-path-specification’ to support
> “single-item search paths” that basically designate a single file.
>
Yes, but some conflicted inputs will bring headahce to builder.
For 'GDK_PIXBUF_MODULE_FILE', both gdk-pixbuf and librsvg have
loaders.cache file, how we ensure the one from librsvg is selected?

> Or we could come up with a different mechanism, but it’s not clear to me
> what that would be.
I have no idea about now too.

Thanks!