Bug: Multi-file KUBECONFIG fails with HELM_DIFF_THREE_WAY_MERGE=true - regression in v3.14.0

[R-omk]

Problem:
Multi-file KUBECONFIG fails with HELM_DIFF_THREE_WAY_MERGE=true (regression in v3.14.0)

Error:

Error: kubernetes cluster unreachable: stat /path/to/file1:/path/to/file2:/path/to/file3: no such file or directory

Affected: v3.14.0, v3.15.0+
Working: v3.13.2 and earlier

Reproduce:

export KUBECONFIG=/path/file1:/path/file2:/path/file3

HELM_DIFF_THREE_WAY_MERGE=true \
HELM_DIFF_NORMALIZE_MANIFESTS=true \
HELM_DIFF_USE_UPGRADE_DRY_RUN=true \
helm diff upgrade my-release my-chart --kube-context=ctx --values values.yaml

Root Cause:

In k8s.io/cli-runtime/pkg/genericclioptions/config_flags.go:166-167:

if f.KubeConfig != nil {
    loadingRules.ExplicitPath = *f.KubeConfig  // ❌ No filepath.SplitList()
}

Then in k8s.io/client-go/tools/clientcmd/loader.go:208:

if _, err := os.Stat(rules.ExplicitPath); os.IsNotExist(err) {
    return nil, err  // ❌ os.Stat() on "file1:file2:file3" string
}

When ExplicitPath is set, the path isn't split. os.Stat() is called on the entire colon-separated string instead of individual files.

Timeline:

• v3.13.2 (Nov 2025): Working with k8s.io/cli-runtime 0.34.1
• v3.14.0 (Nov 17, 2025): Helm v4 support added - BROKEN
• v3.15.0+ (Feb 2026): k8s.io/client-go 0.35.x + k8s.io/cli-runtime 0.35.x - STILL BROKEN

Workaround:

KUBECONFIG=/path/to/single-config-file  # Use single file