'--with-input', '--with-git-url' etc. cause unnecessary rebuilds

DoneSubmitted by Ludovic Courtès.
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  • Ludovic Courtès
  • Ludovic Courtès
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Ludovic Courtès wrote on 7 Nov 2019 13:35
‘--with-input’ causes unintended rebuilds
(address . bug-Guix@gnu.org)
87eeyjsw3g.fsf@inria.fr
Hello,
Consider this example:
Toggle snippet (12 lines)$ guix build glib -nd/gnu/store/9zz9hvzaz06f40a4cbvhskb183x676w4-glib-2.60.6.drv$ guix build glib --with-input=inkscape=libreoffice -nd/gnu/store/15f9jkpakmsaz8i2a0gy4kir1zyk29vi-glib-2.60.6.drv$ guix describeGeneracio 114 Nov 02 2019 11:32:51 (nuna) guix ab1c063 repository URL: https://git.savannah.gnu.org/git/guix.git branch: master commit: ab1c063ab08e069fbe62919828fa634a2e222bbf
Since GLib does not depend on Inkscape, the ‘--with-input’ flag shouldhave no effect: we should get the same glib derivation. However, we’renot.
If we diff the ‘glibc-2.60.6-guile-builder’ files of each derivation, wesee that the second one has a duplicate entry:
(define %build-inputs `(… ("python" . "/gnu/store/78w7y0lxar70j512iqw8x3nimzj10yga-python-3.7.4") ("python" . "/gnu/store/78w7y0lxar70j512iqw8x3nimzj10yga-python-3.7.4") …))
whereas the first one doesn’t have this duplicate entry. IOW, the twoderivations are functionally equivalent but are not bit-identical.
Indeed, evaluating:
(bag-transitive-inputs (package->bag ((package-input-rewriting '()) glib)))
shows that we have two “python” packages there that are not ‘eq?’.
To be continued…
Ludo’.
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Ludovic Courtès wrote on 8 Nov 2019 22:06
(address . 38100@debbugs.gnu.org)
87ftiydqnb.fsf@gnu.org
Hi,
Ludovic Courtès <ludovic.courtes@inria.fr> skribis:
Toggle quote (7 lines)> Indeed, evaluating:>> (bag-transitive-inputs> (package->bag ((package-input-rewriting '()) glib)))>> shows that we have two “python” packages there that are not ‘eq?’.
The problem is that ‘glib’ depends on ‘python-libxml2’, which uses‘python-build-system’ and thus has ‘python’ as an implicit input.
‘package-input-rewriting’ doesn’t touch implicit inputs so it leavesthat implicit ‘python’ untouched.
Since ‘transitive-inputs’ (used by ‘bag-transitive-inputs’) uses pointerequality, we end up with two “python” packages that are not ‘eq?’ butare functionally equivalent: the one produced by‘package-input-rewriting’, and the implicit dependency of‘python-libxml2’. QED.
(This is essentially the same as https://bugs.gnu.org/30155.)
I’m not sure how to address it.
Ludo’.
L
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Ludovic Courtès wrote on 2 Jul 00:14 +0200
control message for bug #38100
(address . control@debbugs.gnu.org)
878sg2yjbj.fsf@gnu.org
merge 38100 42156quit
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Ludovic Courtès wrote on 2 Jul 00:15 +0200
(address . control@debbugs.gnu.org)
87zh8ix4o8.fsf@gnu.org
severity 38100 importantquit
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Ludovic Courtès wrote on 3 Aug 16:30 +0200
control message for bug #42156
(address . control@debbugs.gnu.org)
87tuxjssyb.fsf@gnu.org
retitle 42156 '--with-input', '--with-git-url' etc. cause unnecessary rebuildsquit
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Ludovic Courtès wrote on 27 Sep 23:46 +0200
Re: bug#38100: ‘--with-input’ causes unintended rebuilds
(address . 38100-done@debbugs.gnu.org)
87sgb2dhap.fsf@inria.fr
Hey there!
Ludovic Courtès <ludo@gnu.org> skribis:
Toggle quote (23 lines)> Ludovic Courtès <ludovic.courtes@inria.fr> skribis:>>> Indeed, evaluating:>>>> (bag-transitive-inputs>> (package->bag ((package-input-rewriting '()) glib)))>>>> shows that we have two “python” packages there that are not ‘eq?’.>> The problem is that ‘glib’ depends on ‘python-libxml2’, which uses> ‘python-build-system’ and thus has ‘python’ as an implicit input.>> ‘package-input-rewriting’ doesn’t touch implicit inputs so it leaves> that implicit ‘python’ untouched.>> Since ‘transitive-inputs’ (used by ‘bag-transitive-inputs’) uses pointer> equality, we end up with two “python” packages that are not ‘eq?’ but> are functionally equivalent: the one produced by> ‘package-input-rewriting’, and the implicit dependency of> ‘python-libxml2’. QED.>> (This is essentially the same as <https://bugs.gnu.org/30155>.)
Good news, this is fixed by 2bf6f962b91123b0474c0f7123cd17efe7f09a66,which introduces package rewriting including implicit inputs!
Before getting there, this issue did get on my nerves for a while. Hereare several ways to address this issue that I thought of:
1. Have ‘package-input-rewriting/spec’ traverse implicit inputs, at least optionally. We wouldn’t end up with an equivalent-but-not-eq? ‘python’ in the example above. It does change the semantics though, and it may be nice to keep a “shallow” replacement option. That’s what 2bf6f962b91123b0474c0f7123cd17efe7f09a66 does.
2. Do (delete-duplicates input-drvs) in ‘bag->derivation’. That seems wise, but it’s unfortunately impossible on ‘master’ because of https://issues.guix.gnu.org/43508.
3. ‘package-input-rewriting/spec’ preserves eq?-ness for packages not transformed; in the example above, the transformation result would be eq? to ‘glib’ because ‘--with-input=libreoffice=inkscape’ had no effect. Tricky to implement efficiently, perhaps not worth it.
I think #2 might still be worth investigating, but it may haveundesirable implications too. #3 is hardly doable.
All in all, I’m glad that #1 addresses the issue, because it’s alsosomething we wanted anyway.
Ludo’.
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