Improve document.Selector's String method

This change adds additional output to a document.Selector's String
method, making it easier to find information about the selector being
used. This is particularly helpful when reporting errors, such as those
in #145.

Change-Id: Ic3e67e7597776feec328ad4f54fdf06df863d928
Closes: #145

pkg/document/selectors.go

@@ -1,6 +1,7 @@
 package document
 
 import (
+	"fmt"
 	"strings"
 
 	"sigs.k8s.io/kustomize/v3/pkg/gvk"
@@ -64,6 +65,39 @@ func (s Selector) ByAnnotation(annotationSelector string) Selector {
 	return s
 }
 
+// String is a convenience function which dumps all relevant information about a Selector in the following format:
+// [Key1=Value1, Key2=Value2, ...]
+func (s Selector) String() string {
+	var components []string
+	if s.Group != "" {
+		components = append(components, fmt.Sprintf("Group=%q", s.Group))
+	}
+	if s.Version != "" {
+		components = append(components, fmt.Sprintf("Version=%q", s.Version))
+	}
+	if s.Kind != "" {
+		components = append(components, fmt.Sprintf("Kind=%q", s.Kind))
+	}
+	if s.Namespace != "" {
+		components = append(components, fmt.Sprintf("Namespace=%q", s.Namespace))
+	}
+	if s.Name != "" {
+		components = append(components, fmt.Sprintf("Name=%q", s.Name))
+	}
+	if s.AnnotationSelector != "" {
+		components = append(components, fmt.Sprintf("Annotations=%q", s.AnnotationSelector))
+	}
+	if s.LabelSelector != "" {
+		components = append(components, fmt.Sprintf("Labels=%q", s.LabelSelector))
+	}
+
+	if len(components) == 0 {
+		return "No selection conditions specified"
+	}
+
+	return fmt.Sprintf("[%s]", strings.Join(components, ", "))
+}
+
 // NewEphemeralCloudDataSelector returns selector to get BaremetalHost for ephemeral node
 func NewEphemeralCloudDataSelector() Selector {
 	return NewSelector().ByKind(SecretKind).ByLabel(EphemeralUserDataSelector)

pkg/document/selectors_test.go

@@ -78,3 +78,41 @@ func TestSelectorsSkip(t *testing.T) {
 		}
 	})
 }
+
+func TestSelectorString(t *testing.T) {
+	tests := []struct {
+		name     string
+		selector document.Selector
+		expected string
+	}{
+		{
+			name:     "unconditional",
+			selector: document.Selector{},
+			expected: "No selection conditions specified",
+		},
+		{
+			name:     "by-name",
+			selector: document.NewSelector().ByName("foo"),
+			expected: `[Name="foo"]`,
+		},
+		{
+			name: "by-all",
+			selector: document.NewSelector().
+				ByGvk("testGroup", "testVersion", "testKind").
+				ByNamespace("testNamespace").
+				ByName("testName").
+				ByAnnotation("testAnnotation=true").
+				ByLabel("testLabel=true"),
+			expected: `[Group="testGroup", Version="testVersion", Kind="testKind", ` +
+				`Namespace="testNamespace", Name="testName", ` +
+				`Annotations="testAnnotation=true", Labels="testLabel=true"]`,
+		},
+	}
+
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.expected, tt.selector.String())
+		})
+	}
+}