This makes use of both the existing interfaces and could use the
existing cache file but we'll create a new one and cleanup the old one
to avoid issues and use a more consistent name.
After all our recent troubles with DBM I figured I'd benchmark the
performance of DBM vs. JSON. At read time (what we care more about) the
performance is pretty much identical and JSON is only 1.5x slower at
write time. This seems worth it for the reliability increases to avoid
messing with unreliable native code.
Rather than using the name of the keg for the key use the full path.
This provides several advantages:
- there's no need to invalidate the cache on a `brew upgrade` or
`brew switch`
- it's easier to figure out what cache entries can be removed and this
can be done whenever a keg is removed by `brew uninstall` or
`brew cleanup`.
Also, ensure that an `install` (or `reinstall`, `upgrade`) always
results in the cache being rebuilt for that keg (in case different
options were used).
Cache all the non-weak dynamic library links for a keg rather than the
result of running `brew linkage`. This means that we correctly handle
changes to e.g. what non-keg files are present on disk.
