Dear Maintainer,

For a few days now, I can not use aptitude to keep up-to-date my sid
on my old desktop computers. It works perfectly on my others sid computers
(laptop, VMs).

1)
Using the TUI, after the selection process, when trying to upgrade or install, I only got:

Exception : ../../src/ui.cc:1549: void auto_fix_broken(): Assertion "resman->resolver_exists()" failed.

2)
Using the CUI "LANG=C aptitude upgrade" I got the suspicious following ERROR:

'''
The following packages have unmet dependencies:
 libvtk9.3 : Breaks: libvtk9.1 (< 9.3.0+dfsg1-1) but it is not going to be installed
*** ERROR: search aborted by fatal exception.  You may continue
           searching, but some solutions will be unreachable.

I want to resolve dependencies, but no dependency resolver was created.The following NEW packages will be installed:
  libvtk9.3{ab} libvtk9.3-qt{a} qml6-module-qtquick-effects{a}
....
'''

 I flagged it "important", as on this computer, aptitude is useless,
but it looks like a rare occurence (race condition on slow computer ?
settings (I masked packagekitd) ?)

I am using "apt upgrade" or "apt full-upgrade" directly and it seems to
work perfectly.

"apt install --reinstall aptitude" change nothing.

I do "apt-get source aptitude" to try to get hints, but as I am just
an aptitude source newbie, I do not yet understand when the aptitude_resolver
should created, and why it is not.

Dear Maintainer,

Some bugs evaporate when you look at them...

After my today's "apt full-upgrade", the errors vanished. May be a
transient error related to a failed or incomplete upgrade state ?

Anyway, I guess you may close this bug as, thus, it looks like very
difficult to investigate it more, at least for me.

Thanks for all your works !

I'm getting this error too, so I wouldn't rush to close the bug. In
fact I'd consider bumping to serious since it's making aptitude nearly
unusable.

I can reproduce it in the scenario where I need to activate the
Resolve to resolve conflicts, requiring to go to e (Examine) or !
(Apply).

For instance at the moment to upgrade vtk9 from
9.1.0+really9.1.0+dfsg2-8 to 9.3.0+dfsg1-1, it needs to install
libvtk9.3 ("Actions: 1 install").  I select '!' to Apply the
suggestion (to install libvtk9.3), then press 'g' to start the upgrade.

At this point aptitude crashes with

Uncaught exception: ../../src/ui.cc:1549: void auto_fix_broken(): Assertion "resman->resolver_exists()" failed.

With respect to the crash when upgrading vtk9, the issue (on my
system) appears to be that opencv is not yet rebuilt against the new
vtk9 library (bin-NMU for the libvtk9.3 transition), so no package
resolution is available yet.

But this should not be causing aptitude to crash.