>>: Faré >: Robert >> I strongly recommend against erroring in the .asd file itself based on >> the implementation, because that hinders cross-compilation. > > IIUC what this boils down to is a preference for failing to *operate* on > the system, rather than failing to parse the system definition. Correct? > If we ever want to support cross-compilation, it's more than a preference: it's a bug to fail to load an .asd file just because the system won't load on the current (master) implementation — it is meant to work on the (slave) cross-implementation.
> [As an aside, there may be a separate bug: when I tried to load DecLt > into ACL, the loading *succeeded*, but the contents of the decLt "core" > subsystem failed to be loaded. So I believe there may be an oddity in > the way ASDF is handling these "failed" :feature dependencies. I will > try to replicate and provide a minimal test case.] > I'd say it's a bug in DecLt rather than ASDF. It's :if-feature :sbcl says that the system is a NOP when the target implementation isn't sbcl. If what is intended instead is that the system should error out when the implementation isn't sbcl, it should use something like :depends-on (... (:feature (:not :sbcl) "implementation-not-supported") ...) or to be cleaner: :components ((:file "implementation-not-supported" :if-feature (:not :sbcl))) >> The traditional solution is to load a file that fails. >> i.e. create a file unsupported-implementation.lisp that >> has an (error ...) form and in your asd file, use a component >> (:file "unsupported-implementation" :if-feature (:not :sbcl)) > > I would prefer that we provide a more readable version of this. I think > we could readily add > > (:depends-on (:essential-feature :sbcl)) > I don't like that name, and I don't like abusing :depends-on for it. If you want an error when compiling outside a given set of implementations, maybe it's better having a defsystem option. it doesn't make sense at the component level, so let's not hack the depends-on language for it. (defsystem declt ... :error-if-not-feature :sbcl ...) :(fail|error)-(if-not|unless)(|-feature) :only-build-(on|with-feature) :demand-feature > As I said earlier, the "bogus file" solution seems to me unpleasantly > indirect, because then the poor reader must grovel over > "unsupported-implementation" to see what will happen if one tries to > load it, when the intent is simply to say "this won't work unless you > are on SBCL." > That's quite a reasonable feature request. I was only describing the current "best practice". > I believe we could provide this with the semantics you propose (fail on > operation, not on loading the system definition). > You could fail while building the plan, rather than performing it. Building a plan is already feature-dependent. That would save users a lot of patiently waiting for dependencies to build until they get their doomed answer. —♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org Live as if you were living already for the second time and as if you had acted the first time as wrongly as you are about to act now! — Viktor Frankl, "Man's Search for Meaning"
