Create a kmeta package for libraries acting on ObjectMeta. (#67)

This bootstraps this package with a useful collection of label methods for managing sub-resources.  I'd initially written this as a way of managing versioned DaemonSet resources as part of WarmImage ([see here](62cad8045a/pkg/reconciler/warmimage/resources/meta.go (L28))).

I am upstreaming this here because I want to take advantage of it in Build for managing Image cache subresources of [Cluster]BuildTemplate resources.

kmeta/OWNERS

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+# The OWNERS file is used by prow to automatically merge approved PRs.
+
+approvers:
+- mattmoor
+- jonjohnsonjr

kmeta/doc.go

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+/*
+Copyright 2018 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    https://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package kmeta provides Knative utilities for operating on Kubernetes
+// resources' ObjectMeta.
+package kmeta

kmeta/labels.go

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+/*
+Copyright 2018 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package kmeta
+
+import (
+	"fmt"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/labels"
+	"k8s.io/apimachinery/pkg/selection"
+)
+
+// The methods in this file are used for managing subresources in cases where
+// a controller instantiates different resources for each version of itself.
+//
+// For example, if an A might instantiate N B's at version 1 and M B's at
+// version 2 then it can use MakeVersionLabels to decorate each subresource
+// with the appropriate labels for the version at which it was instantiated.
+//
+// During reconciliation, MakeVersionLabelSelector can be used with the
+// informer listers to access the appropriate subresources for the current
+// version of the parent resource.
+//
+// Likewise during reconciliation, MakeOldVersionLabelSelector can be used
+// with the API client's DeleteCollection method to clean up subresources
+// for older versions of the resource.
+
+// MakeVersionLabels constructs a set of labels to apply to subresources
+// instantiated at this version of the parent resource, so that we can
+// efficiently select them.
+func MakeVersionLabels(om metav1.ObjectMeta) labels.Set {
+	return map[string]string{
+		"controller": string(om.UID),
+		"version":    om.ResourceVersion,
+	}
+}
+
+// MakeVersionLabelSelector constructs a selector for subresources
+// instantiated at this version of the parent resource.  This keys
+// off of the labels populated by MakeVersionLabels.
+func MakeVersionLabelSelector(om metav1.ObjectMeta) labels.Selector {
+	return labels.SelectorFromSet(MakeVersionLabels(om))
+}
+
+// MakeOldVersionLabelSelector constructs a selector for subresources
+// instantiated at an older version of the parent resource.  This keys
+// off of the labels populated by MakeVersionLabels.
+func MakeOldVersionLabelSelector(om metav1.ObjectMeta) labels.Selector {
+	return labels.NewSelector().Add(
+		mustNewRequirement("controller", selection.Equals, []string{string(om.UID)}),
+		mustNewRequirement("version", selection.NotEquals, []string{om.ResourceVersion}),
+	)
+}
+
+// mustNewRequirement panics if there are any errors constructing our selectors.
+func mustNewRequirement(key string, op selection.Operator, vals []string) labels.Requirement {
+	r, err := labels.NewRequirement(key, op, vals)
+	if err != nil {
+		panic(fmt.Sprintf("mustNewRequirement(%v, %v, %v) = %v", key, op, vals, err))
+	}
+	return *r
+}

kmeta/labels_test.go

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+/*
+Copyright 2018 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package kmeta
+
+import (
+	"testing"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+func TestMakeVersionLabels(t *testing.T) {
+	tests := []struct {
+		name string
+		om   metav1.ObjectMeta
+		s    string
+	}{{
+		name: "simple translation",
+		om: metav1.ObjectMeta{
+			UID:             "1234",
+			ResourceVersion: "abcd",
+		},
+		s: "controller=1234,version=abcd",
+	}, {
+		name: "another simple translation",
+		om: metav1.ObjectMeta{
+			UID:             "abcd",
+			ResourceVersion: "1234",
+		},
+		s: "controller=abcd,version=1234",
+	}}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			ls := MakeVersionLabels(test.om)
+			if want, got := test.s, ls.String(); got != want {
+				t.Errorf("MakeVersionLabels() = %v, wanted %v", got, want)
+			}
+		})
+	}
+}
+
+func TestMakeVersionLabelSelector(t *testing.T) {
+	tests := []struct {
+		name string
+		om   metav1.ObjectMeta
+		s    string
+	}{{
+		name: "simple translation",
+		om: metav1.ObjectMeta{
+			UID:             "1234",
+			ResourceVersion: "abcd",
+		},
+		s: "controller=1234,version=abcd",
+	}, {
+		name: "another simple translation",
+		om: metav1.ObjectMeta{
+			UID:             "abcd",
+			ResourceVersion: "1234",
+		},
+		s: "controller=abcd,version=1234",
+	}}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			ls := MakeVersionLabelSelector(test.om)
+			if want, got := test.s, ls.String(); got != want {
+				t.Errorf("MakeVersionLabelSelector() = %v, wanted %v", got, want)
+			}
+		})
+	}
+}
+
+func TestMakeOldVersionLabelSelector(t *testing.T) {
+	tests := []struct {
+		name string
+		om   metav1.ObjectMeta
+		s    string
+	}{{
+		name: "simple translation",
+		om: metav1.ObjectMeta{
+			UID:             "1234",
+			ResourceVersion: "abcd",
+		},
+		s: "controller=1234,version!=abcd",
+	}, {
+		name: "another simple translation",
+		om: metav1.ObjectMeta{
+			UID:             "abcd",
+			ResourceVersion: "1234",
+		},
+		s: "controller=abcd,version!=1234",
+	}}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			ls := MakeOldVersionLabelSelector(test.om)
+			if want, got := test.s, ls.String(); got != want {
+				t.Errorf("MakeOldVersionLabelSelector() = %v, wanted %v", got, want)
+			}
+		})
+	}
+}