Unclear behavior of matchRegistryUrls / registryUrls for docker datasource packages

[SeWieland]

How are you running Renovate?

None

Which platform you running Renovate on?

GitLab (.com or self-hosted)

Which version of Renovate are you using?

43.129.0

Please tell us more about your question or problem

In #41966 a great new feature was added - matchRegistryUrls as a package rule.

I'm not quite sure if I can replace and improve my existing docker package rule here, as docker dependencies typically come with the registry name right inside the packageName. Example:

{
  "matchDatasources": ["docker"],
  "matchPackageNames": [
    "!registry.gitlab.example.com{/,}**",
    "!*.artifactory.example.com{/,}**"
  ],
  "registryUrls": ["https://docker.artifactory.example.com"]
}

I used this rule to point any already compliant image registries to the company default "https://docker.artifactory.example.com".
But in the following example, only the first dependency is resolved as intended, as the registry name is baked into the packageName:

# renovate: datasource=docker depName=traefik1 packageName=ghcr-io.artifactory.example.com/traefik/traefik versioning=helm
TAEFIK_VERSION: 39.0.0

# renovate: datasource=docker depName=traefik2 packageName=traefik/traefik versioning=helm registryUrl=ghcr-io.artifactory.example.com
TAEFIK_VERSION: 39.0.0

Can I now use this as as drop-in replacement that handles both cases and is thus more robust?
Or would it now only work in the second case, as the first one does not explicitly specify any registryUrl?
(And does the registryUrl actually would have to start with https:// as its an URL scheme per definition?)

{
  "matchDatasources": ["docker"],
  "matchRegistryUrls": [
    "!{https://,}registry.gitlab.example.com{/,}**",
    "!{https://,}*.artifactory.example.com{/,}**",
  ]
  "registryUrls": ["https://docker.artifactory.example.com"]
}

I also would love to actually drop all those package rules and use registryAliases instead - but all my most of my deps are parsed using custom regex Managers...

[viceice]

docker datasource doesn't handle registryUrls well, you should avoid that and use proper packageName and / or registryAliases.

[SeWieland]

Thanks for the answer, that is what I suspected.
To me that behavior unclear when looking through the docs. Also https://docs.renovatebot.com/modules/datasource/docker/ does not mention this custom registry quirk / inconsistency to other data sources in any way.

I think matchRegistryUrls is a great new feature, but the docs have some room for improvement here