apt and do-release-upgrade question - what's sources.list.distUpgrade for?

[Chris Green]

On Mon, Jul 20, 2020 at 12:43:40PM +0200, Ralf Mardorf via ubuntu-users wrote:
> On Mon, 20 Jul 2020 10:36:41 +0100, Chris Green wrote:
> >Ignoring the stuff in the sources.list.d (though that follows the same
> >pattern), what is sources.list.distUpgrade?  I can see that
> >sources.list.save is just my old/previous sources.list renamed which
> >is handy to see if anything needs re-enabling after the upgrade.
> 
> "sources.list.distUpgrade" is a backup of the old sources list.
> "sources.list" and "sources.list.save" are _not_ a backup of the old
> source list.
> 
Well the names are rather confusing then! :-)

[snip sensible comments about why it's difficult to manage this]

Surely "sources.list.distUpgrade" should be called
"sources.list.backup" or "sources.list.oldVersion" or something like
that?  ... and if "sources.list.save" isn't a backup then what is it?

On my system after doing do-release-upgrade "sources.list.save" and
"sources.list.distUpgrade" are identical.

-- 
Chris Green