Anonymous build reporting

[edsko]

There is partial support for uploading build reports and build logs. This needs to be extended and should include anonymous build reports that the cabal-install client can generate (currently we only support the non-anonymous/detailed build reports). This way we can gather huge amounts of data on what packages work in what circumstances. We can use that to help inform maintainers and users and to edit package dependencies to match reality.

[dcoutts]

Doing the anonymous reports in such a way that it preserves anonymity requires a bit of care. Anyone wanting to tackle this should ask for details about a scheme that we think will work.

The point is we cannot publish the anonymous reports directly immediately because that reveals too much (timing, ordering etc). So we should hold back all reports for a certain time (e.g. a day) and then randomly reorder them all before making the data publicly available.