Packaging: why does the RPM spec have both Provides & Obsoletes for the same packages?

[Dridi Boukelmoune]

Hey Geoff,

On Tue, Aug 24, 2021 at 2:40 PM Geoff Simmons <geoff at uplex.de> wrote:
>
> Hello,
>
> The spec file for RPM packages:
>
> https://raw.githubusercontent.com/varnishcache/pkg-varnish-cache/master/redhat/varnish.spec
>
> ... has this passage:
>
> Provides:  varnish-libs%{?_isa} = %{version}-%{release}
> Provides:  varnish-libs = %{version}-%{release}
> Obsoletes: varnish-libs
>
> Provides:  varnish-docs = %{version}-%{release}
> Obsoletes: varnish-docs
>
> Provides:  varnish-debuginfo%{?_isa} = %{version}-%{release}
> Provides:  varnish-debuginfo = %{version}-%{release}
> Obsoletes: varnish-debuginfo
>
> This may be an RPM technique that I'm not familiar with, but why does it
> have both Provides and Obsoletes for -libs, -docs and -debuginfo?
>
> Since the Obsoletes don't specify a version, my best guess is that it's
> something about updating to newer versions. But wouldn't newer versions
> (newer version and RPM release number) be enough for that?

They should ideally provide a version, but since we have packaging
that could compete with first party packages we can't really predict
what version we would go against.

Keeping Provides doesn't break an installation of -docs for example,
because ultimately the package containing the docs is going to be
installed thanks to the Provides.

> Asking because I'm building a custom RPM package for which I'd also like
> to have the debuginfo. Creating the debuginfo RPM is easy enough, by
> removing this line from the spec:
>
> %global debug_package %{nil}
>
> But then when you try to run debuginfo-install, it says that the
> debuginfo package is obsoleted by the Varnish package.
>
> I can get the debuginfo to install by removing the Obsoletes line for
> varnish-debuginfo, and rebuilding the RPMs. But I'm confused about why
> it was there in the first place, and concerned that I may have broken
> something else by doing so.

I think the reason why we didn't want the traditional separation
debuginfo package was the poor quality of panic backtraces. Once
split, installing the separate debuginfo wouldn't improve the
backtraces.

I think this specific point was a result of:

https://github.com/varnishcache/varnish-cache/commit/95437e6c882f2c2b332be94060a7ac96907db322

It's been a while, I don't remember the details.

Cheers,
Dridi