fix(list): scrub list returned from .List()

This way only the latest release is displayed with `helm list`.

Signed-off-by: Matthew Fisher <matt.fisher@microsoft.com>

cmd/helm/testdata/output/list-all.txt

@@ -5,6 +5,5 @@ groot      	default  	1       	2016-01-16 00:00:01 +0000 UTC	uninstalled    	chi
 hummingbird	default  	1       	2016-01-16 00:00:03 +0000 UTC	deployed       	chickadee-1.0.0
 iguana     	default  	2       	2016-01-16 00:00:04 +0000 UTC	deployed       	chickadee-1.0.0
 rocket     	default  	1       	2016-01-16 00:00:02 +0000 UTC	failed         	chickadee-1.0.0
-starlord   	default  	1       	2016-01-16 00:00:01 +0000 UTC	superseded     	chickadee-1.0.0
 starlord   	default  	2       	2016-01-16 00:00:01 +0000 UTC	deployed       	chickadee-1.0.0
 thanos     	default  	1       	2016-01-16 00:00:01 +0000 UTC	pending-install	chickadee-1.0.0

pkg/action/list.go

@@ -171,6 +171,8 @@ func (l *List) Run() ([]*release.Release, error) {
 		return results, nil
 	}
 
+	results = filterList(results)
+
 	// Unfortunately, we have to sort before truncating, which can incur substantial overhead
 	l.sort(results)
 
@@ -218,6 +220,30 @@ func (l *List) sort(rels []*release.Release) {
 	}
 }
 
+// filterList returns a list scrubbed of old releases.
+func filterList(rels []*release.Release) []*release.Release {
+	idx := map[string]int{}
+
+	for _, r := range rels {
+		name, version := r.Name, r.Version
+		if max, ok := idx[name]; ok {
+			// check if we have a greater version already
+			if max > version {
+				continue
+			}
+		}
+		idx[name] = version
+	}
+
+	uniq := make([]*release.Release, 0, len(idx))
+	for _, r := range rels {
+		if idx[r.Name] == r.Version {
+			uniq = append(uniq, r)
+		}
+	}
+	return uniq
+}
+
 // setStateMask calculates the state mask based on parameters.
 func (l *List) SetStateMask() {
 	if l.All {