fix: reuse only user-supplied values when no values flag is given (#464) - #1087

Fixes #464

helm diff upgrade without any --set/--values flag does not show changes made to the chart's own values.yaml. For a release installed from a local chart, editing a value in values.yaml gives an empty diff, while helm upgrade does apply the change.

Cause

When no value flag is given, template() in cmd/helm.go fetches the values of the release with helm get values --all and passes them to helm template as --values. With --all that output is the fully coalesced values, so it contains the whole values.yaml of the chart the release was installed from. A --values file takes precedence over the values.yaml of the new chart, so every changed default is overridden by its old value. (The root cause was worked out by @antoineozenne in the issue.)

This is what helm upgrade --reuse-values does, not what helm upgrade does by default. In reuseValues() the default case is only:

if len(newVals) == 0 && len(current.Config) > 0 {
    newVals = current.Config
}

current.Config holds the user-supplied values. The chart's values are left alone.

Fix

Without --reuse-values, fetch the values without --all, which is current.Config. If the release has no user-supplied values, helm get values prints null, and no --values is passed at all. --reuse-values still uses --all, and --reset-then-reuse-values already fetched without --all. The same code runs with HELM_DIFF_USE_UPGRADE_DRY_RUN=true, so that mode is fixed too.

Behaviour change

The default diff now includes changes to the chart's default values. A diff that used to be empty can now show changes, and --detailed-exitcode then returns 2 for it. Those are the changes helm upgrade makes. User-supplied values of the release are still kept, as before.

Tests

• TestUpgradeCommand_Execution_ReuseValues: the case "existing release without value flags" from fix: skip --reuse-values for a release that is not installed (#481) #1086 expected helm get values --all. It now expects the call without --all, since that expectation was this bug. Two new cases cover HELM_DIFF_USE_UPGRADE_DRY_RUN and a release without user-supplied values, where helm get values prints null and no --values may be passed. All cases now also check whether --values reaches the render command. The three default-path cases fail on master. The fake helm can print a separate output for helm get values through HELM_DIFF_FAKE_VALUES_OUTPUT.
• I ran the built binary as a plugin with Helm v3.17.3 and v4.3.0 against a local kube-apiserver and etcd (no kubelet). The chart has one ConfigMap. I installed one release without values and one with --set user=from-install, then changed a default in values.yaml and added a new key. For each row I compared helm diff upgrade with helm upgrade --dry-run=server:

Both Helm versions give the same results. Only the two rows without flags change. With only an existing value edited, helm diff upgrade --allow-unreleased prints an empty diff on master and the changed line with this PR.

• make format, make lint and make test pass, and golangci-lint v2.14.0 reports 0 issues.

Not tested: a kind cluster, so the CI integration job has not been run locally. I did not add a scripts/issues/464.sh; I can add one if you want it.

Not part of this PR

• Diff is incorrect when values in values.yaml change and --reuse-values is used #457 is not fixed. With --reuse-values, a key that is new in the chart's values.yaml still appears in the diff, because a --values file can only be merged over the new chart's values and Helm replaces them.
• With HELM_DIFF_USE_UPGRADE_DRY_RUN=true, --reset-values is not passed on to helm upgrade, so a release with user-supplied values keeps them in the diff. That is the same before and after this change.