Unstructed helpers: document lack of slice syntax

staging/src/k8s.io/apimachinery/pkg/apis/meta/v1/unstructured/helpers.go

@@ -32,6 +32,9 @@ import (
 // NestedFieldCopy returns a deep copy of the value of a nested field.
 // Returns false if the value is missing.
 // No error is returned for a nil field.
+//
+// Note: fields passed to this function are treated as keys within the passed
+// object; no array/slice syntax is supported.
 func NestedFieldCopy(obj map[string]interface{}, fields ...string) (interface{}, bool, error) {
 	val, found, err := NestedFieldNoCopy(obj, fields...)
 	if !found || err != nil {
@@ -43,6 +46,9 @@ func NestedFieldCopy(obj map[string]interface{}, fields ...string) (interface{},
 // NestedFieldNoCopy returns a reference to a nested field.
 // Returns false if value is not found and an error if unable
 // to traverse obj.
+//
+// Note: fields passed to this function are treated as keys within the passed
+// object; no array/slice syntax is supported.
 func NestedFieldNoCopy(obj map[string]interface{}, fields ...string) (interface{}, bool, error) {
 	var val interface{} = obj
 

staging/src/k8s.io/apimachinery/pkg/apis/meta/v1/unstructured/helpers_test.go

@@ -67,6 +67,11 @@ func TestNestedFieldNoCopy(t *testing.T) {
 			"b": target,
 			"c": nil,
 			"d": []interface{}{"foo"},
+			"e": []interface{}{
+				map[string]interface{}{
+					"f": "bar",
+				},
+			},
 		},
 	}
 
@@ -91,13 +96,13 @@ func TestNestedFieldNoCopy(t *testing.T) {
 	assert.Nil(t, res)
 
 	// case 4: field does not exist
-	res, exists, err = NestedFieldNoCopy(obj, "a", "e")
+	res, exists, err = NestedFieldNoCopy(obj, "a", "g")
 	assert.False(t, exists)
 	assert.Nil(t, err)
 	assert.Nil(t, res)
 
 	// case 5: intermediate field does not exist
-	res, exists, err = NestedFieldNoCopy(obj, "a", "e", "f")
+	res, exists, err = NestedFieldNoCopy(obj, "a", "g", "f")
 	assert.False(t, exists)
 	assert.Nil(t, err)
 	assert.Nil(t, res)
@@ -108,6 +113,13 @@ func TestNestedFieldNoCopy(t *testing.T) {
 	assert.False(t, exists)
 	assert.Nil(t, err)
 	assert.Nil(t, res)
+
+	// case 7: array/slice syntax is not supported
+	//         (background: users may expect this to be supported)
+	res, exists, err = NestedFieldNoCopy(obj, "a", "e[0]")
+	assert.False(t, exists)
+	assert.Nil(t, err)
+	assert.Nil(t, res)
 }
 
 func TestNestedFieldCopy(t *testing.T) {