Function to set labels.

api/filters/filtersutil/filtersutil.go

@@ -5,11 +5,25 @@ package filtersutil
 
 import (
 	"encoding/json"
+	"sort"
 
 	"sigs.k8s.io/kustomize/kyaml/kio"
 	"sigs.k8s.io/kustomize/kyaml/yaml"
 )
 
+// SortedMapKeys returns a sorted slice of keys to the given map.
+// Writing this function never gets old.
+func SortedMapKeys(m map[string]string) []string {
+	keys := make([]string, len(m))
+	i := 0
+	for k := range m {
+		keys[i] = k
+		i++
+	}
+	sort.Strings(keys)
+	return keys
+}
+
 // ApplyToJSON applies the filter to the json objects.
 func ApplyToJSON(filter kio.Filter, objs ...marshalerUnmarshaler) error {
 	var nodes []*yaml.RNode

api/filters/filtersutil/filtersutil_test.go

@@ -11,6 +11,32 @@ import (
 	"sigs.k8s.io/kustomize/kyaml/yaml"
 )
 
+func TestSortedKeys(t *testing.T) {
+	testCases := map[string]struct {
+		input    map[string]string
+		expected []string
+	}{
+		"empty": {
+			input:    map[string]string{},
+			expected: []string{}},
+		"one": {
+			input:    map[string]string{"a": "aaa"},
+			expected: []string{"a"}},
+		"three": {
+			input:    map[string]string{"c": "ccc", "b": "bbb", "a": "aaa"},
+			expected: []string{"a", "b", "c"}},
+	}
+	for tn, tc := range testCases {
+		t.Run(tn, func(t *testing.T) {
+			if !assert.Equal(t,
+				filtersutil.SortedMapKeys(tc.input),
+				tc.expected) {
+				t.FailNow()
+			}
+		})
+	}
+}
+
 func TestApplyToJSON(t *testing.T) {
 	instance1 := bytes.NewBufferString(`{"kind": "Foo"}`)
 	instance2 := bytes.NewBufferString(`{"kind": "Bar"}`)