Track runner spec updates with an actionable revision (#4638)

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

controllers/actions.github.com/helpers.go

@@ -1,10 +1,44 @@
 package actionsgithubcom
 
 import (
+	"github.com/actions/actions-runner-controller/apis/actions.github.com/v1alpha1"
 	corev1 "k8s.io/api/core/v1"
 	apiequality "k8s.io/apimachinery/pkg/api/equality"
 )
 
+// ephemeralRunnerSetActionableSpecChanged reports whether the runner spec the
+// EphemeralRunnerSet is running differs from the one derived from the
+// AutoscalingRunnerSet, in a way that requires re-applying it to the runners.
+//
+// Semantic.DeepEqual is used rather than cmp.Equal or reflect.DeepEqual because
+// it treats a nil slice/map as equal to an empty one. That matters here: most
+// PodSpec collection fields carry omitempty, so a template containing an
+// explicitly empty value (`env: []`) is dropped when the EphemeralRunnerSet is
+// written and reads back as nil. A strict comparison would report drift on every
+// single reconcile, bumping ActionableRevision each time and making the
+// EphemeralRunnerSet controller delete every idle and pending runner, forever.
+// Semantic also knows how to compare resource.Quantity, and unlike cmp.Equal it
+// cannot panic on types with unexported fields.
+func ephemeralRunnerSetActionableSpecChanged(current, desired *v1alpha1.EphemeralRunnerSet) bool {
+	if current == nil || desired == nil {
+		return current != desired
+	}
+
+	return !apiequality.Semantic.DeepEqual(current.Spec.EphemeralRunnerSpec, desired.Spec.EphemeralRunnerSpec)
+}
+
+func nextActionableRevision(current *v1alpha1.EphemeralRunnerSet) int64 {
+	if current == nil {
+		return 1
+	}
+
+	if current.Spec.ActionableRevision > current.Status.AppliedActionableRevision {
+		return current.Spec.ActionableRevision + 1
+	}
+
+	return current.Status.AppliedActionableRevision + 1
+}
+
 // listenerPodSpecRequiresRecreation reports whether the live listener pod must be
 // deleted and rebuilt to match the desired spec.
 //