Search paths vs. environment variables that designate a single file

[ludo@gnu.org (Ludovic Courtès)]

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.

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.

> 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.

One way might be to augment ‘search-path-specification’ to support
“single-item search paths” that basically designate a single file.

Or we could come up with a different mechanism, but it’s not clear to me
what that would be.

Thoughts?

Thanks,
Ludo’.