[bug#40993] cuirass: Add build products download support.

[Mathieu Othacehe]

Hola!

> For the record, in Hydra, build products would be found if there’s a
> special ‘nix-support/hydra-build-products’ file in the output.  The
> advantage is that it’s more flexible, but the downside is that you’d
> have to adjust your derivations specifically for that.

Yes, I first hesitated to replicate this mechanism but finally opted for
the implemented one. I didn't like so much the idea of adding and extra,
CI-specific file, to the output of some jobs.

> Use ‘for-each’ if it’s for effects, as seems to be the case.

Oh you keep repeating that to me, and I keep doing the same mistake!

> Regarding #:sha256-hash: there’s a somewhat standard format to represent
> hashes and their algorithms as strings, but I forgot the name.  Like,
> you’d write “sha256-” followed by a base64 string, something like that.
>
> Perhaps it’d be wiser to use it rather than hard-code sha256?

Yes sure, I changed the database field to "checksum" so that we can use
the string representation you're talking about.

> Also, we don’t really have tests for the web UI, I don’t know how much
> work it’d be to add tests.

If a more web-aware hacker could propose something, it would be great
indeed :)

> Apart from that, I have little to say, other than the fact that it’s
> really cool.  :-)

Thanks for reviewing! I just pushed those two commits and updated the
Cuirass package.  Now I'll see with Marius or Ricardo how to update
Berlin, I guess.

Thanks,

Mathieu