Enhance the libyear output in Renovate logs

[justo-mend]

Background

Recently, Renovate CLI was enhanced to capture and report on dependency health using libyears.
[More info about libyears can be found here. - "A simple measure of software dependency freshness. It is a single number telling you how up-to-date your dependencies are."]

Proposal

Enhance the libyears calculations in Renovate CLI in the following ways:

1. De-duplicate dependencies - to avoid double-counting the libyears of an individual package
2. Provide additional related information about the dependencies in the repo

Duplication

Sometimes a package and its version are declared in more than one package file, resulting in duplication.
Rather than counting the libyears for those dependencies multiple times, it would be best to de-duplicate the packages so that each distinct package is counted only once.

Additional information

Information captured and reported about dependency health could be extended to include other useful information, including:

• Total number of dependencies
• Total number of out-of-date dependencies
  This can help provide a better picture of the state of the repository's dependency health.

[RahulGautamSingh]

Total number of dependencies

If there is a dep in two package files with diffferent version in each. Should it be counted once or twice?

And, if it is counted once. Should we take the lowest or highest version for libYears calculation?

I think we use the one with the lowest version.

[mkniewallner]

Hi, really like this feature. I think it makes a lot of sense to have that directly in Renovate, as all the infrastructure for extracting dependencies is already in place.

Are there plans to make the output usable for a machine usage, by for instance making it possible to write it down to a JSON file?

[rarkins]

At this point our preferred approach is to log such things and recommend JSON logging if you want to parse it