Generalise pmb.helpers.other.cache with a more python decorator.
The Cache decorator takes a list of function arguments to use as cache
keys, keyword args can be used to restrict caching so that it is skipped
entirely unless the attribute has a specific value.
For example, pmb.helpers.pmaports.get() has the decorator:
@Cache("pkgname", subpackages=True)
This means the return value will be cached only when subpackages is
True, otherwise it will always miss.
Signed-off-by: Caleb Connolly <caleb@postmarketos.org>
Introduce helpers for interacting with pkgrepos (e.g. pmaports, and
others). These allow pmbootstrap to handle multiple source repositories.
Signed-off-by: Caleb Connolly <caleb@postmarketos.org>
