Support option for only LTS releases in datasource "endoflife-date"

[mikaello]

Problem

Some packages has long term support (LTS) releases, but the information that a given package is LTS is often only available as some information in a table on the website of the package (see prometheus website for example), while the datasource for releases have no such information (e.g. GitHub tags for prometheus). This is often mitigated by having a manually maintained Renovate config like this:

  "packageRules": [
     {
       "matchPackageNames": ["prometheus/prometheus"],
       "allowedVersions": "<2.46.0"
     }
  ]

Question / possible solution

The datasource endoflife-date is based on https://endoflife.date/, in the endoflife API they have the field lts which contains information on if this is an LTS release or not (see prometheus releases as example). Would it be possible to specify an option to the endoflife-date datasource that it should only consider LTS-versions?

[mikaello]

An option/workaround is to create a custom datasource like:

"customDatasources": {
  "prometheus-lts": {
    "defaultRegistryUrlTemplate": "https://endoflife.date/api/prometheus.json",
    "transformTemplates": [
      "{\"releases\": $[lts=true].{\"version\": \"v\" & latest,\"sourceUrl\": \"https://github.com/prometheus/prometheus\"},\"homepage\": \"https://prometheus.io\"}"
    ]
  }
}

[rarkins]

Related: #27632

With the above feature, it would mean "if currently on an LTS release then don't propose updates to non-LTS".

The next step would be to add LTS status to supported datasources/packages, similar in concept to the stable/unstable concept we already have.

Using your example, Renovate is currently using the github-tags datasource for prometheus/prometheus: https://github.com/prometheus/prometheus/tags

And the corresponding EOL data is https://endoflife.date/api/prometheus.json

Is the EOL website accurate and up-to-date enough to use it completely instead of the github-tags? Or we'd need to blend these two? I suspect you're asking to switch to EOL in cases like this, and even if it's not perfectly up-to-date then you'd prefer to wait until they have data about a release anyway?