SLCORE-2238 Add on-demand plugin storage infrastructure

[Krosovok]

No description provided.

[sonar-review-alpha]

Summary

Adds foundational infrastructure for on-demand plugin storage. Introduces DownloadableArtifact enum to define downloadable plugins (C-family, C#, OmniSharp) with version management and URL pattern generation, and OnDemandPluginCacheManager to manage plugin cache lifecycle by deleting version directories older than 60 days while preserving the current version. Includes a test dependency (system-stubs-jupiter) for mocking system properties during testing.

What reviewers should know

Start with DownloadableArtifact.java — it's the core abstraction that maps artifact keys to versions and download URLs. Note the three OmniSharp entries have TODO comments and incomplete URL patterns ("TBA"), indicating future work. The properties files are templates/fixtures that versions will be injected into during the build. OnDemandPluginCacheManager uses file modification time to determine age, so understand that the 60-day retention window is based on last-modified rather than creation time. The test fixture versions (cfamily 6.50.0, csharp 9.32.0) match the main properties template. No actual downloads or caching logic is implemented yet — this PR establishes the data model and cleanup infrastructure.

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[hashicorp-vault-sonar-prod]

SLCORE-2238

[sonar-review-alpha]

Conclusion: The cache cleanup logic is clean and well-tested, but there's a latent runtime crash in DownloadableArtifact that needs fixing before this is merged.

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[sonar-review-alpha]

The three OmniSharp entries reference version keys (omnisharp.mono.version, omnisharp.net6.version, omnisharp.win.version) that are absent from ondemand-plugins.properties. Calling version() on any of them throws IllegalStateException at runtime — the guard on line 53 makes it fail loudly, not silently. Since byArtifactKey is public and these artifact keys are real lookup strings, any caller that resolves an OmniSharp artifact and then calls version() will blow up in production.

Either add placeholder entries in the properties file (even empty/commented-out ones with a clear TODO) so the failure surface is obvious, or don't add the OmniSharp entries to the enum until their version and URL are defined.

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[Copilot]

Pull request overview

Adds initial infrastructure for on-demand plugin storage by introducing a cache cleanup manager, a registry of downloadable artifacts, and a resource file intended to provide artifact versions.

Changes:

• Introduce OnDemandPluginCacheManager and unit tests to clean up old cached plugin versions based on retention.
• Add DownloadableArtifact enum to describe downloadable artifacts and load their versions from a classpath properties file.
• Add ondemand-plugins.properties as the source of artifact version values.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
backend/core/src/main/java/org/sonarsource/sonarlint/core/plugin/ondemand/OnDemandPluginCacheManager.java	New cache cleanup logic for removing old plugin-version directories.
backend/core/src/test/java/org/sonarsource/sonarlint/core/plugin/ondemand/OnDemandPluginCacheManagerTest.java	New unit tests covering cleanup behavior for missing/current/old/recent version dirs.
backend/core/src/main/java/org/sonarsource/sonarlint/core/plugin/ondemand/DownloadableArtifact.java	New artifact registry that loads version strings from a properties resource and builds URLs.
backend/core/src/main/resources/ondemand-plugins.properties	New properties file intended to provide versions for on-demand artifacts.

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[sonarqube-next]

Quality Gate passed

Issues
0 New issues
6 Accepted issues

Measures
0 Security Hotspots
0 Dependency risks
80.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

[sonar-review-alpha]

Conclusion: The misleading "LRU" comment has been corrected, but the OmniSharp runtime-crash issue flagged in the previous round is still unresolved.

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[nquinquenel]

I'd put the binaries URL as a static var

[nquinquenel]

I think we need the full version here, with the build, no?

[nquinquenel]

Edit: I noticed the other PR, I guess this is temporary