Hello Ricardo, Ricardo Wurmus <rek...@elephly.net> writes:
> Hi Guix, > > today on IRC someone reported an ugly error message when reconfiguring > their system: > > Backtrace: > 18 (primitive-load "/home/me/.config/guix/current/bin/…") > In guix/ui.scm: > 2209:7 17 (run-guix . _) > 2172:10 16 (run-guix-command _ . _) > In ice-9/boot-9.scm: > 1752:10 15 (with-exception-handler _ _ #:unwind? _ # _) > In guix/status.scm: > 822:3 14 (_) > 802:4 13 (call-with-status-report _ _) > In guix/scripts/system.scm: > 1256:4 12 (_) > In ice-9/boot-9.scm: > 1752:10 11 (with-exception-handler _ _ #:unwind? _ # _) > In guix/store.scm: > 658:37 10 (thunk) > 1320:8 9 (call-with-build-handler #<procedure 7fecaf8570c0 at g…> …) > 2123:24 8 (run-with-store #<store-connection 256.99 7fecb75c7230> …) > In guix/scripts/system.scm: > 827:2 7 (_ _) > 703:7 6 (_ #<store-connection 256.99 7fecb75c7230>) > In gnu/system.scm: > 1227:19 5 (operating-system-derivation _) > In gnu/services.scm: > 1091:6 4 (instantiate-missing-services _) > In srfi/srfi-1.scm: > 460:18 3 (fold #<procedure 7fecb73c0960 at gnu/services.scm:109…> …) > In gnu/services.scm: > 1092:27 2 (_ (#<<service> type: #<service-type gdm 7fecbd17f6…> …) …) > In ice-9/boot-9.scm: > 1685:16 1 (raise-exception _ #:continuable? _) > 1685:16 0 (raise-exception _ #:continuable? _) > > ice-9/boot-9.scm:1685:16: In procedure raise-exception: > In procedure struct-vtable: Wrong type argument in position 1 (expecting > struct): > > As you can probably tell easily by looking at this message, the > “service” field of the operating system configuration looked something > like this: > > (services (append (list a b c %desktop-services) #;oops)) > > instead of this > > (services (append (list a b c) %desktop-services)) > > This is because INSTANTIATE-MISSING-SERVICES — and FOLD-SERVICES, and > many more — assumes that it is only passed a plain list of services. It > then proceeds to call SERVICE-KIND on what may or may not be a service. > > I think we should add simple type checks, something like this: > > (define (listof pred) > (lambda (thing) > (and (list? thing) (every pred thing)))) > … > (define (assert-type type-check thing message) > (or (false-if-exception (type-check thing)) > (report-error (G_ "type error: …\n" message)))) > > ;; Use ASSERT-TYPE in an example procedure. > (define (do-something-with-services services) > (assert-type (listof service?) services > "SERVICES must be a list of <service> values.") > > ;; Do things… > (map service-kind services)) > > What do you think? There are many different ways of implementing this > (a new variant of DEFINE that also accepts a type declaration, an assert > like above, a fancier assert that composes a helpful error message by > itself, a separate type declaration that is looked up only when the > corresponding procedure is called in a certain context, etc), but I’d > first like to know if there is consensus that we want something like > this. I hear we now have "field sanitizers" on Guix records; without having dug the details, it seems to be we could add a predicate validating the input there? The nice thing about it is that it'd be a one place change, instead of asserts to sprinkle around various places. Thanks, Maxim
