feat(helm): Support Helm v4 for rendering and deployment, drop Helm v2 support for rendering since helm version --client parameter is not supported anymore in v4

[AndiDog]

Fixes: #9871
Related: n/a
Merge before/after: n/a

Description

Using the Helm v4 prerelease builds doesn't work right now due to breaking changes in the post-renderer support. Instead of passing --post-renderer /path/to/skaffold, a plugin must be registered (see #9871). This PR supports Helm v4 by adding v3-vs-v4 distinction code. Along the way, since deployer code already needs a minimum of Helm v3.1, I drop support for Helm v2 in the render code because helm version doesn't support --client as parameter anymore.

Since 1) multiple Skaffold binaries could be installed on a system, particularly development builds, and 2) package managers like homebrew won't require helm and install a post-renderer plugin manifest, I opted to instead have Skaffold do the needed helm plugin install UNIQUE_PLUGIN_NAME call on the fly (and clean up after every use).

Minor stuff: consistent variable naming helmVersion, tiny docs typo fix

User facing changes (remove if N/A)

• Helm v2 won't work anymore
• Helm v4 works now

Follow-up Work (remove if N/A)

• I didn't change documentation yet. The PR is already large, so I'd like to check any Helm version hints in Skaffold docs later.
• On arm64, I couldn't run make integration-in-kind and certain other targets. Maybe an integration smoke test for Helm v4 makes sense?

[gemini-code-assist]

Summary of Changes

Hello @AndiDog, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request updates Skaffold's Helm integration to be compatible with Helm v4, which introduced significant changes to how post-renderers are handled. It also removes support for older Helm v2 versions, streamlining the codebase and ensuring compatibility with modern Helm practices. The core change involves adapting Skaffold to manage Helm v4's new plugin-based post-renderer system on the fly, ensuring a smooth user experience without requiring manual plugin installation.

Highlights

• Helm v4 Support: Skaffold now supports Helm v4 for both rendering and deployment, addressing breaking changes in its post-renderer mechanism.
• Helm v2 Deprecation: Support for Helm v2 rendering has been dropped due to the removal of the --client parameter in helm version in newer Helm versions.
• Dynamic Helm Plugin Management: For Helm v4, Skaffold dynamically installs a temporary post-renderer plugin and cleans it up after use, bypassing the need for manual plugin registration.

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[gemini-code-assist]

Code Review

This pull request introduces support for Helm v4 by adapting to its new post-renderer plugin system, and as a consequence, drops support for Helm v2. The changes are well-structured, with the new logic for handling Helm v4 plugins encapsulated in PreparePostRenderer. The codebase is also improved by renaming variables for clarity (e.g., bV to helmVersion) and updating tests and documentation accordingly.

My review focuses on the new plugin handling logic. I've found a couple of issues in the implementation of the temporary plugin creation and cleanup that could lead to resource leaks or confusing error messages. I've also pointed out corresponding corrections needed in the test files. Overall, this is a great contribution to keep Skaffold up-to-date with the Helm ecosystem.

[mattsanta]

Could you address the failing checks?

[AndiDog]

@mattsanta Tests look green now. I had to introduce another test-related override variable to ensure that no real helm command is attempted. Lints also fixed.

[AndiDog]

@mattsanta now that Helm v4 is officially released, can Skaffold also be released?

[mattsanta]

Yep, working on it. @AndiDog