[Aptitude-devel] Bug#995256: Bug#995256: aptitude: TUI loops "Can't find a source to download ..." error

[Axel Beckert]

Hi IOhannes,

IOhannes m zmoelnig wrote:
> - aptitude opens new *red* window where it prints
> 
> > E: Can't find a source to download version 'VERSION' of 'PACKAGE'
> 
> - the error window grows as one such line is printed about every 500ms
>   until it finally fills the entire height of the screen

I think I've seen that once or twice, too, but way to seldom to
actually bother as I considered it to be caused by inconsistencies
outside aptitude.

> - quitting aptitude and restarting it makes the problem go away

Hmmmm.

> I have no idea why this happens, but originally thought it might be related to
> not having run 'update' as a first step.

I'd rather imagine something the other way round:

I wonder if there is a kind of race condition if aptitude is running
and then either on the admin on the commandline or a background job
runs "apt update".

> in the meantime i'm not so sure about this anymore (e.g. as i think i don't have
> to run 'update' in the restarted aptitude).

No, you don't have to. Aptitude more or less just reads what files are
in /var/lib/apt/lists/ (and some more state files).

> in any case, i have not been able to find a way to reliably reproduce the
> problem (it just happens every now and then).

Ack.

> i've seen this problem for a "long time" by now (probably pre 2021)

Yes, haven't seen it recently.

> i've attached a screenshot.

Thanks! There's an interesting fact visible. First let's look at that
package:

  ~ → apt-cache show texlive-fonts-recommended
  Package: texlive-fonts-recommended
  Source: texlive-base
  Version: 2021.20210921-1
  Installed-Size: 15031
  Maintainer: Debian TeX Task Force <debian-tex-maint at lists.debian.org>
  Architecture: all

So this package in question is arch:all.

But according to the screenshot, aptitude wants
texlive-fonts-recommended:amd64 for whatever reason — which indeed
does not exist. So it's probably _not_ related to updating package
lists in the background.

And yes, I've recently seen such an issue elsewhere, namely here:
https://salsa.debian.org/debian/zsh/-/jobs/1950702#L1463

The relevant lines are:

  The following packages have unmet dependencies:
  zsh-cross-build-deps:arm64 : Depends: cm-super-minimal:arm64 which is a virtual package and is not provided by any available package
  Unable to resolve dependencies!  Giving up...

(And yes, cm-super-minimal is arch:all as well.)

Then again, the above was already during dependency resolution and not
in the preview. It though still might be caused by the same bug mixing
up arch:all with arch:any packages as the above error message stems
from src/cmdline/cmdline_resolver.cc and hence is commandline-specific.

I tried to fix this in zsh like this:
https://salsa.debian.org/debian/zsh/-/commit/801f5e105ad6d1f767d28c8311edd263790f419f

And it indeed fixed the crossbuild CI check:
https://salsa.debian.org/debian/zsh/-/jobs/1946010

But unfortunately then on the buildds it failed for the arch:all build
with "B-D uninstallable" (note the missing 5.8-8 upload on
https://buildd.debian.org/status/logs.php?pkg=zsh&arch=all) and I had
to revert that "fix".

> Architecture: amd64 (x86_64)
> Foreign Architectures: i386

I wonder if this is a multiarch related bug since the case I mentioned
above was a cross-build and hence also has multiarch involved.

		Regards, Axel
-- 
 ,''`.  |  Axel Beckert <abe at debian.org>, https://people.debian.org/~abe/
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