GNU bug report logs - #65225
‘guix shell --system=ALIEN’ builds for both systems

Previous Next

Full log

View this message in rfc822 format

From: Josselin Poiret <dev <at> jpoiret.xyz>
To: Tobias Geerinckx-Rice <me <at> tobias.gr>, 65225 <at> debbugs.gnu.org
Cc: Tobias Geerinckx-Rice <me <at> tobias.gr>, Simon Tournier <zimon.toutoune <at> gmail.com>, Mathieu Othacehe <othacehe <at> gnu.org>, Ludovic Courtès <ludo <at> gnu.org>, Christopher Baines <mail <at> cbaines.net>, Ricardo Wurmus <rekado <at> elephly.net>
Subject: bug#65225: [PATCH] environment: Build the profile for the requested system.
Date: Sat, 12 Aug 2023 12:42:59 +0200

[Message part 1 (text/plain, inline)]

Hi everyone,

Actually, let me add a big erratum, since it appears I misread the
intention of gexp->derivation (and realized 2 minutes after writing the
previous email).

Josselin Poiret <dev <at> jpoiret.xyz> writes:
> --8<---------------cut here---------------start------------->8---
> (mlet* %store-monad ( ;; The following binding forces '%current-system' and
>                      ;; '%current-target-system' to be looked up at >>=
>                      ;; time.
>                      (graft?    (set-grafting graft?))
>
>                      (system -> (or system (%current-system)))
>                      (target -> (if (eq? target 'current)
>                                     (%current-target-system)
>                                     target))
>                      ...)
>   ...)
> --8<---------------cut here---------------end--------------->8---
>
> Well, the issue here is that such an mlet starts by translating the
> graft? binding into a >>= call, which ends up putting the rest of the
> translation into a function call that will *not* be called until the
> monadic value is run.  That means that the system and target bindings
> afterwards are *not* looked up at call time but at monadic run time!

This is actually what the comment above hints at, I misunderstood its
meaning.  It seems that this piece of code used to be (before 2015)

--8<---------------cut here---------------start------------->8---
(mlet* %store-monad ( ;; The following binding forces '%current-system' and
                     ;; '%current-target-system' to be looked up at >>=
                     ;; time.
                     (unused    (return #f)

                     (system -> (or system (%current-system)))
                     (target -> (if (eq? target 'current)
                                    (%current-target-system)
                                    target))
                     ...)
  ...)
--8<---------------cut here---------------end--------------->8---

probably at a time when (current-system) didn't exist.  In turn, this
means that gexp->derivation intentionally delays getting the current
system to monadic run time.  Thus, we probably need to pass an optional
#:system argument to the hooks that they can forward to
gexp->derivation to fix this “properly”

> IMO, this is way too complicated to keep in mind at all times, and there
> are bugs lurking under the surface absolutely everywhere, waiting for a
> corner case to be uncovered.

My comment still stands.

Best,
-- 
Josselin Poiret

[signature.asc (application/pgp-signature, inline)]

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.