[solved] Re: SimpleBackportCreation attempt says: The value 'unstable' is invalid for APT::Default-Release

[David <bouncingcats@gmail.com>]

Hi, first thank-you to everyone who replied for taking an interest in
assisting me and improving Debian guides. I feel very lucky to have access
to you folks here with expertise and experience plus the goodwill to help
someone without expecting anything in return.

I will summarise and respond to all in this one message.

First, thank-you to AlexandreRossi who has already updated the Debian wiki
page with the fix suggested by Andrei POPESCU. So other readers please note
that the current wiki page is different to the one that prompted my initial
request for help. That older incorrect version of page as it was at my time
of writing can be viewed here:

  https://wiki.debian.org/SimpleBackportCreation?action=recall&rev=73

Thanks to Reco for confirmation that the problem wasn't one of my own
creation (typically it is, because I tend to forget things), and suggesting
adding a deb..unstable line to sources.list with the caution not to run
'apt upgrade'.

In fact this is exactly what I was curious about, because I was attracted
to the wiki method because it appeared to avoid that risk, and so I was
keen to follow the wiki method, and then motivated to ask here why it
apparently worked for the wiki authors but not for me.

Thanks also to Reco for showing me 'sudo apt build-dep cgdb', yes that
worked here.

Thanks to Andrei for locating a relevant bug report
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=441178#75
and suggesting this workaround:

  $ apt source cgdb/unstable

I confirm that worked here, thank you!

As an aside, how did you find this, I am very curious, what are people's
methods for searching for bugs? Because over the years I have tried on many
occasions to search at https://www.debian.org/Bugs/ for various things but
I just never feel comfortable with the interface there (eg why is the
search restricted by suite) and I never seem to have much success at
finding anything useful. Does anyone have any tips for successful bug
searching?

Thanks to Greg for warning about the dangers of adding a deb..unstable
line, yes I am aware that can cause a frankendebian disaster.

About a decade ago I spent a couple of years lurking in freenode #bash
where Greg was an amazing contributor, so I have seen what situations
trigger Greg's frustrations when offering assistance. I realise now that
I could have simplified my question by testing and submitting with
a sources list that used deb.debian.org as a server instead of the approx
proxy-cache, but I've been using approx for so long that I just forgot that
it might obfuscate the issue, so I apologise for that.

Greg thanks for providing a worked example, but I was disappointed that you
did not actually test the command given on the wiki page, the one that
failed for me. In your example, you used

  $ apt-get source ksh

How do you know which suite that command downloads the source from?
I found myself wishing that you had tested the command that actually failed
for me in my posted question:

  $ apt source -t unstable cgdb

That's what triggered the bug/error. Does it work for you? I know that you
have an interest in this topic because I saw that you contributed earlier
edits to that wiki page, but they were modified by later contributors.