Report unused variables.

pkg/target/resaccumulator.go

@@ -18,6 +18,9 @@ package target
 
 import (
 	"fmt"
+	"log"
+	"strings"
+
 	"sigs.k8s.io/kustomize/pkg/resid"
 	"sigs.k8s.io/kustomize/pkg/resmap"
 	"sigs.k8s.io/kustomize/pkg/transformers"
@@ -135,8 +138,18 @@ func (ra *ResAccumulator) ResolveVars() error {
 	if err != nil {
 		return err
 	}
-	return ra.Transform(transformers.NewRefVarTransformer(
-		replacementMap, ra.tConfig.VarReference))
+	if len(replacementMap) == 0 {
+		return nil
+	}
+	t := transformers.NewRefVarTransformer(
+		replacementMap, ra.tConfig.VarReference)
+	err = ra.Transform(t)
+	if len(t.UnusedVars()) > 0 {
+		log.Printf(
+			"well-defined vars that were never replaced: %s\n",
+			strings.Join(t.UnusedVars(), ","))
+	}
+	return err
 }
 
 func (ra *ResAccumulator) FixBackReferences() (err error) {

pkg/target/resaccumulator_test.go

@@ -17,6 +17,9 @@ limitations under the License.
 package target_test
 
 import (
+	"bytes"
+	"log"
+	"os"
 	"strings"
 	"testing"
 
@@ -120,6 +123,50 @@ func TestResolveVarsHappy(t *testing.T) {
 	}
 }
 
+func TestResolveVarsOneUnused(t *testing.T) {
+	ra, _, err := makeResAccumulator()
+	if err != nil {
+		t.Fatalf("unexpected err: %v", err)
+	}
+	err = ra.MergeVars([]types.Var{
+		{
+			Name: "SERVICE_ONE",
+			ObjRef: types.Target{
+				Gvk:  gvk.Gvk{Version: "v1", Kind: "Service"},
+				Name: "backendOne"},
+		},
+		{
+			Name: "SERVICE_UNUSED",
+			ObjRef: types.Target{
+				Gvk:  gvk.Gvk{Version: "v1", Kind: "Service"},
+				Name: "backendTwo"},
+		},
+	})
+	if err != nil {
+		t.Fatalf("unexpected err: %v", err)
+	}
+	var buf bytes.Buffer
+	log.SetOutput(&buf)
+	defer func() {
+		log.SetOutput(os.Stderr)
+	}()
+	err = ra.ResolveVars()
+	if err != nil {
+		t.Fatalf("unexpected err: %v", err)
+	}
+	expectLog(t, buf, "well-defined vars that were never replaced: SERVICE_UNUSED")
+	c := getCommand(find("deploy1", ra.ResMap()))
+	if c != "myserver --somebackendService backendOne --yetAnother $(SERVICE_TWO)" {
+		t.Fatalf("unexpected command: %s", c)
+	}
+}
+
+func expectLog(t *testing.T, log bytes.Buffer, expect string) {
+	if !strings.Contains(log.String(), expect) {
+		t.Fatalf("expected log containing '%s', got '%s'", expect, log.String())
+	}
+}
+
 func TestResolveVarsVarNeedsDisambiguation(t *testing.T) {
 	ra, rf, err := makeResAccumulator()
 	if err != nil {