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Subject: |
‘--with-input’ causes unintended rebuilds |
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Date: |
Thu, 07 Nov 2019 13:35:15 +0100 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) |
Hello,
Consider this example:
--8<---------------cut here---------------start------------->8---
$ 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 describe
Generacio 114 Nov 02 2019 11:32:51 (nuna)
guix ab1c063
repository URL: https://git.savannah.gnu.org/git/guix.git
branch: master
commit: ab1c063ab08e069fbe62919828fa634a2e222bbf
--8<---------------cut here---------------end--------------->8---
Since GLib does not depend on Inkscape, the ‘--with-input’ flag should
have no effect: we should get the same glib derivation. However, we’re
not.
If we diff the ‘glibc-2.60.6-guile-builder’ files of each derivation, we
see 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 two
derivations 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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--- Begin Message ---
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Subject: |
Re: bug#38100: ‘--with-input’ causes unintended rebuilds |
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Date: |
Sun, 27 Sep 2020 23:46:22 +0200 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) |
Hey there!
Ludovic Courtès <ludo@gnu.org> skribis:
> 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. Here
are 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 have
undesirable implications too. #3 is hardly doable.
All in all, I’m glad that #1 addresses the issue, because it’s also
something we wanted anyway.
Ludo’.
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