[bug#60802] [PATCH v2 1/2] platforms: Raise an exception when no suitable platform is found.

[Ludovic Courtès]

Hi,

Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:

> This was motivated by #60786, which produced a cryptic, hard to understand
> backtrace.
>
> * guix/platform.scm (&platform-not-found-error): New exception type.
> (make-platform-not-found-error): New exception constructor.
> (platform-not-found-error?): New predicate.
> (false-if-platform-not-found): New syntax.
> (lookup-platform-by-system): Raise an exception when no platform is found.
> Update documentation.
> (lookup-platform-by-target): Likewise.
> (lookup-platform-by-target-or-system): Likewise, and guard lookup calls with
> false-if-platform-not-found.

Sounds like a good idea!

> +++ b/gnu/packages/bootstrap.scm
> @@ -315,7 +315,7 @@ (define* (glibc-dynamic-linker
>                                   (%current-system))))
>    "Return the name of Glibc's dynamic linker for SYSTEM."
>    ;; See the 'SYSDEP_KNOWN_INTERPRETER_NAMES' cpp macro in libc.
> -  (let ((platform (lookup-platform-by-system system)))
> +  (let ((platform (false-if-exception (lookup-platform-by-system system))))

Maybe we don’t need to protect here, because it’s a 

> +++ b/guix/platform.scm
> @@ -21,6 +21,7 @@ (define-module (guix platform)
>    #:use-module (guix memoization)
>    #:use-module (guix records)
>    #:use-module (guix ui)
> +  #:use-module (ice-9 exceptions)

So far the we use (srfi srfi-35) exclusively to define condition types;
I think we should do the same here, for consistency.

> +            &platform-not-found-error
> +            make-platform-not-found-error

The constructor doesn’t need to be exposed.

> +;;;
> +;;; Exceptions.
> +;;;
> +(define-exception-type &platform-not-found-error &error
> +  make-platform-not-found-error platform-not-found-error?)

So this would become (define-condition-type …).

Otherwise LGTM, thanks!

Ludo’.