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.
1. Running `brew linkage some_package` does not set the cache.
2. Running `brew linkage --cached some_package` when `DatabaseCache.empty?` returns `true` should build the cache.
3. Running `brew linkage --cached some_package` when `DatabaseCache.empty?` returns `false` should use the cache.
Ensure that a non-zero exit code is set both for missing random dylibs
and random missing dependencies.
Additionally, while we are here, drastically trim down the public
interface for this class to the bare minimum and allow getting the
output from `display_test_output` as a variable.
Fixes issue mentioned by @ilovezfs in:
https://github.com/Homebrew/brew/pull/3940#issuecomment-383794520
1. In "display_test_output": when printing dependencies without
linkage, use "Dependencies with no linkage" string instead of "Possible
unnecessary dependencies" for consistency with "display_normal_output"
2. In "check_dylibs": keep track of and skip repetitive checking of
those dylibs that have been previously checked. This is applicable when
different executables/libraries are linked against the same libraries.
3. In "check_undeclared_deps": when there are missing libraries,
corresponding dependencies should be excluded from the list of
dependencies with no linkage.
