Add structcheck, unused, and varcheck linters.

Warn on unused and dead code

Signed-off-by: Daniel Nephin <dnephin@gmail.com>

snapshot/overlay/overlay.go

@@ -38,13 +38,6 @@ type snapshotter struct {
 	ms   *storage.MetaStore
 }
 
-type activeSnapshot struct {
-	id       string
-	name     string
-	parentID interface{}
-	readonly bool
-}
-
 // NewSnapshotter returns a Snapshotter which uses overlayfs. The overlayfs
 // diffs are stored under the provided root. A metadata file is stored under
 // the root.

snapshot/storage/metastore_test.go

@@ -444,11 +444,6 @@ func testCommit(ctx context.Context, t *testing.T, ms *MetaStore) {
 	assertNotActive(t, err)
 }
 
-func testCommitNotExist(ctx context.Context, t *testing.T, ms *MetaStore) {
-	_, err := CommitActive(ctx, "active-not-exist", "committed-1", snapshot.Usage{})
-	assertNotExist(t, err)
-}
-
 func testCommitExist(ctx context.Context, t *testing.T, ms *MetaStore) {
 	if err := basePopulate(ctx, ms); err != nil {
 		t.Fatalf("Populate failed: %+v", err)

snapshot/testsuite/issues.go

@@ -99,6 +99,7 @@ func checkChown(ctx context.Context, t *testing.T, sn snapshot.Snapshotter, work
 // checkRename
 // https://github.com/docker/docker/issues/25409
 func checkRename(ctx context.Context, t *testing.T, sn snapshot.Snapshotter, work string) {
+	t.Skip("rename test still fails on some kernels with overlay")
 	l1Init := fstest.Apply(
 		fstest.CreateDir("/dir1", 0700),
 		fstest.CreateDir("/somefiles", 0700),

snapshot/testsuite/testsuite.go

@@ -38,8 +38,7 @@ func SnapshotterSuite(t *testing.T, name string, snapshotterFn func(ctx context.
 	t.Run("RemoveIntermediateSnapshot", makeTest(name, snapshotterFn, checkRemoveIntermediateSnapshot))
 	t.Run("DeletedFilesInChildSnapshot", makeTest(name, snapshotterFn, checkDeletedFilesInChildSnapshot))
 	t.Run("MoveFileFromLowerLayer", makeTest(name, snapshotterFn, checkFileFromLowerLayer))
-	// Rename test still fails on some kernels with overlay
-	//t.Run("Rename", makeTest(name, snapshotterFn, checkRename))
+	t.Run("Rename", makeTest(name, snapshotterFn, checkRename))
 
 	t.Run("ViewReadonly", makeTest(name, snapshotterFn, checkSnapshotterViewReadonly))