storage: correctly handle error during Walk

Signed-off-by: Stephen J Day <stephen.day@docker.com>

registry/storage/walk.go

@@ -38,7 +38,9 @@ func Walk(ctx context.Context, driver storageDriver.StorageDriver, from string,
 		}
 
 		if fileInfo.IsDir() && !skipDir {
-			Walk(ctx, driver, child, f)
+			if err := Walk(ctx, driver, child, f); err != nil {
+				return err
+			}
 		}
 	}
 	return nil

registry/storage/walk_test.go

@@ -41,10 +41,12 @@ func TestWalkErrors(t *testing.T) {
 		t.Error("Expected invalid root err")
 	}
 
+	errEarlyExpected := fmt.Errorf("Early termination")
+
 	err = Walk(ctx, d, "/", func(fileInfo driver.FileInfo) error {
 		// error on the 2nd file
 		if fileInfo.Path() == "/a/b" {
-			return fmt.Errorf("Early termination")
+			return errEarlyExpected
 		}
 		delete(expected, fileInfo.Path())
 		return nil
@@ -52,8 +54,12 @@ func TestWalkErrors(t *testing.T) {
 	if len(expected) != fileCount-1 {
 		t.Error("Walk failed to terminate with error")
 	}
-	if err != nil {
-		t.Error(err.Error())
+	if err != errEarlyExpected {
+		if err == nil {
+			t.Fatalf("expected an error due to early termination")
+		} else {
+			t.Error(err.Error())
+		}
 	}
 
 	err = Walk(ctx, d, "/nonexistant", func(fileInfo driver.FileInfo) error {