feat(registry): implement IsZeroer for Variants

[suzuki-shunsuke]

Summary

Adds an IsZero method to the Variants slice type so it follows the same pattern as the sibling collection types in pkg/config/registry/package_info.go (Overrides, FormatOverrides, Replacements), all of which implement go.yaml.in/yaml/v3.IsZeroer.

Why

Variants was added in #4733 as a named slice type — type Variants []*Variant — but it was the only collection type in the package without an IsZero method. That made the API surface inconsistent with how the rest of the package opts into yaml.v3's zero detection.

go.yaml.in/yaml/v3 calls IsZero() bool during marshal to decide whether a field tagged with omitempty should be emitted. The other collection types in this file each implement it the same way:

// IsZero implements the [go.yaml.in/yaml/v3.IsZeroer] interface.
// It returns true if the Overrides slice is nil.
func (o Overrides) IsZero() bool {
    return o == nil
}

The encoder is exercised by, for example, pkg/controller/generate-registry/generate.go (yaml.NewEncoder(c.stdout, yaml.IndentSequence(true))) when aqua re-emits registry YAML. Without an explicit IsZeroer implementation, behaviour relied on the encoder's reflect-based fallback, which differs subtly from the other collection types — they only treat nil as empty (so an explicit Variants{} would be marshalled as variants: []), while reflection considers a length-0 slice zero too.

What changed

pkg/config/registry/package_info.go:

 // Variants is a list of Variant conditions that must all match for the
 // containing Override to apply.
 type Variants []*Variant

+// IsZero implements the [go.yaml.in/yaml/v3.IsZeroer] interface.
+// It returns true if the Variants slice is nil.
+func (v Variants) IsZero() bool {
+	return v == nil
+}
+
 // Override provides platform-specific package configuration that overrides

That's the entire diff — 6 lines, single file.

Test plan

• cmdx v (go vet) — passes
• cmdx l (golangci-lint) — 0 issues
• go test -count=1 ./pkg/config/registry/... — passes
• Manual: re-emit a registry that contains variants via aqua generate-registry and confirm nil Variants are omitted while explicit empty [] would still be emitted (matches Overrides/FormatOverrides semantics).

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved YAML configuration serialization to omit empty variant configurations from output files, resulting in cleaner and more readable configuration files.

[coderabbitai]

Caution

Review failed

Pull request was closed or merged during review

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: c41ef62c-d1fc-4fd4-a9dd-33dabb8206e2

📥 Commits

Reviewing files that changed from the base of the PR and between 48112d7 and d06c03b.

📒 Files selected for processing (1)

• pkg/config/registry/package_info.go

---

📝 Walkthrough

Walkthrough

An IsZero() method was added to the Variants slice type to enable YAML v3 to correctly identify and omit nil variant values during marshaling operations.

Changes

Cohort / File(s)	Summary
YAML Marshaling Support pkg/config/registry/package_info.go	Added IsZero() method to Variants type to support YAML v3 zero-value detection during marshaling.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

🐰 A method small, yet precise,
Makes YAML marshals oh-so-nice!
When nil variants come to play,
IsZero() clears the way! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: implementing the IsZeroer interface for the Variants type to make it consistent with other collection types in the file.
Description check	✅ Passed	The description is comprehensive and well-structured, covering the summary, rationale, changes made, and test plan. It follows the repository's contribution guidelines and provides clear context for the change.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/variants-iszero

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