backpack: Be more careful when adding together ImportAvails

There was some code in the signature merging logic which added together
the ImportAvails of the signature and the signature which was merged
into it. This had the side-effect of making the merged signature depend
on the signature (via a normal module dependency). The intention was to
propagate orphan instances through the merge but this also messed up
recompilation logic because we shouldn't be attempting to load B.hi when
mergeing it.

The fix is to just combine the part of ImportAvails that we intended to
(transitive info, orphan instances and type family instances) rather
than the whole thing.

0 files changed, 0 insertions, 0 deletions