fix: Rust private registry authentication documentation

[i10416]

Changes

Documentation for Rust private crate authentication

This won't change renovate behavior.

Context

• hostType should be either platform or datasource. For Rust crate, datasource is not cargo, but crate
• registryUrls in packageRules for private crate registry require sparse+ prefix.
  • guess from

    renovate/lib/modules/datasource/crate/index.spec.ts

    Line 368 in dc7b8d9

    const res = await getPkgReleases({

hostType is another way to filter rules and can be either a platform such as github and bitbucket-server, or it can be a datasource such as docker and rubygems.
https://docs.renovatebot.com/configuration-options/

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[rarkins]

I'm really surprised if this works

[i10416]

Thank you for review and sorry for the late response.

Without sparse+ prefix, renovate fails to fetch dependencies trying to run git clone against AWS CodeArtifact, which is not git repository but crates.io compatible registry.
With sparse+, the error from git clone disappears.

Without sparse+ prefix, I guess the program falls into this clause, which causes renovate to invoke git clone.

renovate/lib/modules/datasource/crate/index.ts

Line 296 in 84f5d2a

if (registry.flavor !== 'crates.io' && !registry.isSparse) {

[i10416]

However, as I haven't looked into renovate codebase that deep, I may be wrong.

[rarkins]

In that case please provide a reproduction repo using this format so we can test. It can be a dummy codeartifact URL