feat: Detect missing selector during lint

Signed-off-by: Matt Butcher <matt.butcher@microsoft.com>

pkg/lint/rules/template.go

@@ -131,6 +131,7 @@ func Templates(linter *support.Linter, values map[string]interface{}, namespace
 			linter.RunLinterRule(support.ErrorSev, path, validateYamlContent(err))
 			linter.RunLinterRule(support.ErrorSev, path, validateMetadataName(&yamlStruct))
 			linter.RunLinterRule(support.ErrorSev, path, validateNoDeprecations(&yamlStruct))
+			linter.RunLinterRule(support.ErrorSev, path, validateMatchSelector(&yamlStruct, renderedContent))
 		}
 	}
 }
@@ -185,6 +186,19 @@ func validateNoReleaseTime(manifest []byte) error {
 	return nil
 }
 
+// validateMatchSelector ensures that template specs have a selector declared.
+// See https://github.com/helm/helm/issues/1990
+func validateMatchSelector(yamlStruct *K8sYamlStruct, manifest string) error {
+	switch yamlStruct.Kind {
+	case "Deployment", "ReplicaSet", "DaemonSet", "StatefulSet":
+		// verify that matchLabels or matchExpressions is present
+		if !(strings.Contains(manifest, "matchLabels") || strings.Contains(manifest, "matchExpressions")) {
+			return fmt.Errorf("a %s must contain matchLabels or matchExpressions, and %q does not", yamlStruct.Kind, yamlStruct.Metadata.Name)
+		}
+	}
+	return nil
+}
+
 // K8sYamlStruct stubs a Kubernetes YAML file.
 //
 // DEPRECATED: In Helm 4, this will be made a private type, as it is for use only within

pkg/lint/rules/template_test.go

@@ -145,7 +145,7 @@ func TestDeprecatedAPIFails(t *testing.T) {
 		Templates: []*chart.File{
 			{
 				Name: "templates/baddeployment.yaml",
-				Data: []byte("apiVersion: apps/v1beta1\nkind: Deployment\nmetadata:\n  name: baddep"),
+				Data: []byte("apiVersion: apps/v1beta1\nkind: Deployment\nmetadata:\n  name: baddep\nspec: {selector: {matchLabels: {foo: bar}}}"),
 			},
 			{
 				Name: "templates/goodsecret.yaml",
@@ -226,3 +226,82 @@ func TestStrictTemplateParsingMapError(t *testing.T) {
 		}
 	}
 }
+
+func TestValidateMatchSelector(t *testing.T) {
+	md := &K8sYamlStruct{
+		APIVersion: "apps/v1",
+		Kind:       "Deployment",
+		Metadata: k8sYamlMetadata{
+			Name: "mydeployment",
+		},
+	}
+	manifest := `
+	apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: nginx-deployment
+  labels:
+    app: nginx
+spec:
+  replicas: 3
+  selector:
+    matchLabels:
+      app: nginx
+  template:
+    metadata:
+      labels:
+        app: nginx
+    spec:
+      containers:
+      - name: nginx
+        image: nginx:1.14.2
+	`
+	if err := validateMatchSelector(md, manifest); err != nil {
+		t.Error(err)
+	}
+	manifest = `
+	apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: nginx-deployment
+  labels:
+    app: nginx
+spec:
+  replicas: 3
+  selector:
+    matchExpressions:
+      app: nginx
+  template:
+    metadata:
+      labels:
+        app: nginx
+    spec:
+      containers:
+      - name: nginx
+        image: nginx:1.14.2
+	`
+	if err := validateMatchSelector(md, manifest); err != nil {
+		t.Error(err)
+	}
+	manifest = `
+	apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: nginx-deployment
+  labels:
+    app: nginx
+spec:
+  replicas: 3
+  template:
+    metadata:
+      labels:
+        app: nginx
+    spec:
+      containers:
+      - name: nginx
+        image: nginx:1.14.2
+	`
+	if err := validateMatchSelector(md, manifest); err == nil {
+		t.Error("expected Deployment with no selector to fail")
+	}
+}