[asdf-devel] Ordering of system :depends-on elements

[Zach Beane]

Robert Goldman <rpgoldman at sift.info> writes:

> Zach Beane wrote:
>> Robert Goldman <rpgoldman at sift.info> writes:
>> 
>>> Zach Beane wrote:
>>>> A few projects in quicklisp work something like this:
>>>>
>>>>    ;;; foo.asd
>>>>
>>>>    (defsystem foo ...)
>>>>
>>>>    (defsystem foo-extra ...)
>>>>
>>>>
>>>>    ;;; bar.asd
>>>>
>>>>    (defsystem bar :depends-on (:foo-extra :foo))
>>>>
>>>> With asdf 2, (asdf:load-system "bar") seems to work fine, I guess
>>>> because asdf 2 does the equivalent of find-system on the elements from
>>>> right-to-left.
>>>>
>>>> With asdf 3, it doesn't seem to work fine, I guess because asdf 3 does
>>>> the equivalent of find-system on the elements from left-to-right.
>>>>
>>>> Are those guesses correct?
>>>>
>>>> What's the best way to have a system definition that works equally well
>>>> in asdf2 and asdf3 in this kind of situation?
>>>
>>> I feel like I'm missing something.  Is there some reason you can't simply make 
>>>
>>> (defsystem foo-extra :depends-on (:foo)
>>>   ....)
>>>
>>> ?
>> 
>> If they were in separate files, yes. They aren't.
>
> I misunderstood your original question:  I thought that this was a
> dependency problem, but it's not.  The problem is that the system
> authors depended on something contingent about the way FIND-SYSTEM was
> invoked to find depended-upon systems.  I haven't gone back to check,
> but my guess is that something once iterated and pushed, and now collects.
>
>> This was relied upon by some projects, and now it doesn't work.
>
> I'm sorry, but to the best of my knowledge that behavior was never
> offered up by ASDF to be relied upon.  Programmers  should not have
> depended on this behavior.
>
> The only solution I know of is to break foo.asd into multiple files.  I
> realize that this is inconvenient, but restoring backward compatibility
> involves restoring a state where programmers are relying on a reading
> that is not just contingent, but contingent in a way that encourages
> people to write system definitions in a way that will be actively
> misleading to the reader (since conventionally we read left to right).
>
> Does this happen in enough systems in quicklisp that this is a serious
> problem?  How many?  Perhaps we can work out some solution.  I realize
> that in many cases the one-system-per-file mapping can be a nuisance.

It happens for mcclim-freetype and mcclim-truetype and
mcclim-freetype-cffi and perhaps some others.

Zach