- For some of these I changed `context` to `describe` as it fit better
rather than contriving a "when", "with" or "without", or massively
restructuring the tests.
- Use reference counting so nested `CacheStoreDatabase.use` share the
same underlying database (rather than rereading it every time).
- Only write out the cache database file when it has changed.
- Cleanup cache database entries on formula or full `brew cleanup`.
Fixes#8690
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.
When the DBM database cannot be read by the current version of Ruby's
DBM library (due to corruption or another incompatibility) it segfaults
or freezes which takes down the entire Homebrew Ruby process.
This isn't desirable so instead perform a shell out with the Homebrew
Ruby to see if it can read the DBM database before we try to use the
information. If this hangs or crashes: silently delete the database and
recreate it.
