Create select-build-id-by-build-server-and-derivation-file-name, which just
returns the id, and then a variant that returns more fields for making a page
for each build.
The equivalent_derivations table was an experiment that didn't work, so switch
to using the derivations_by_output_details_set table.
Also take the build server id as input, as this allows selecting derivations
which have no known build for the relevant build server.
Rather than just counting builds where the derivation matches, select builds
based on the derivation outputs, which accounts for different but equivalent
derivations.
Derivations are effectively equivalent if they produce the same set of
outputs, which is possible because of the equivalence of fixed output
derivations. A fixed output derivation can be different, but equivalent,
because it produces the same fixed output.
To better allow tracking equivalent derivations, primarily to allow working
out what derivations might correspond to a build, store the sets of derivation
outputs, and which derivations they relate to.
The join on derivation_outputs was completely wrong, so fix that.
Also, rather than only selecting outputs where there's a corresponding build,
just eliminate outputs where there is an entry in the nars table, fetched from
the relevant build server.
Also just look at x86_64-linux derivations, because there's no filtering on
relevant derivations for a build server at the moment.
Rather than eliminating any derivation that has a known build, eliminate those
derivations, but also equivalent derivations as well.
For selecting the derivations in a revision, join on the equivalent
derivations, as all the equilalent derivations need checking as well, as it's
unknown which one Cuirass would have associated the build against.
Also, filter for x86_64-linux, to avoid checking for crossbuilt things. This
should be replaced by some way of describing what derivations a build server
has.
Duplicate builds could creep in if the code to create them ran concurrently. I
didn't exclude them initially, as I was unsure if there should be such a
restriction, but at least for now, Cuirass builds map exactly to a single
derivation, so use the same restriction here.
