Fixes issue 1392, kpt can't handle kind: List. (#3654)

Co-authored-by: Pieter Emmelot <p.emmelot@gmail.com>

commands/live/apply/cmdapply.go

@@ -175,6 +175,12 @@ func (r *Runner) runE(c *cobra.Command, args []string) error {
 		return err
 	}
 
+	// objs may contain kind List
+	objs, err = live.Flatten(objs)
+	if err != nil {
+		return err
+	}
+
 	invInfo, err := live.ToInventoryInfo(inv)
 	if err != nil {
 		return err

pkg/live/flatten.go

@@ -0,0 +1,42 @@
+// Copyright 2022 Google LLC
+//
+// 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 live
+
+import (
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	"k8s.io/apimachinery/pkg/runtime"
+)
+
+// Flatten returns a list containing 'in' objects with objects of kind List
+// replaced by their members.
+func Flatten(in []*unstructured.Unstructured) ([]*unstructured.Unstructured, error) {
+	var out []*unstructured.Unstructured
+
+	for _, o := range in {
+		if o.IsList() {
+			err := o.EachListItem(func(item runtime.Object) error {
+				item2 := item.(*unstructured.Unstructured)
+				out = append(out, item2)
+				return nil
+			})
+			if err != nil {
+				return nil, err
+			}
+		} else {
+			out = append(out, o)
+		}
+	}
+	return out, nil
+}

pkg/live/flatten_test.go

@@ -0,0 +1,78 @@
+// Copyright 2022 Google LLC
+//
+// 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 live
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+)
+
+func Test_Flatten(t *testing.T) {
+	tests := []struct {
+		name string
+		in   []*unstructured.Unstructured
+		want []*unstructured.Unstructured
+	}{
+		{
+			name: "simple list",
+			in:   simpleList,
+			want: simpleList,
+		},
+		{
+			name: "list with list",
+			in: []*unstructured.Unstructured{
+				{
+					Object: map[string]interface{}{
+						"kind":  "List",
+						"items": anySlice(simpleList),
+					},
+				},
+			},
+			want: simpleList,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := Flatten(tt.in)
+			if assert.NoError(t, err) {
+				assert.Equal(t, tt.want, got)
+			}
+		})
+	}
+}
+
+func anySlice(in []*unstructured.Unstructured) (out []interface{}) {
+	for _, o := range in {
+		out = append(out, o.Object)
+	}
+	return
+}
+
+var simpleList = []*unstructured.Unstructured{
+	{
+		Object: map[string]interface{}{
+			"kind":    "ConfigMap",
+			"version": "v1",
+		},
+	},
+	{
+		Object: map[string]interface{}{
+			"kind":    "Pod",
+			"version": "v1",
+		},
+	},
+}