snapshots: revert default --lastest behavior to pre-0.19.0

the changed behavior now only applies when using `--group-by`.

changelog/unreleased/issue-21869

@@ -0,0 +1,11 @@
+Bugfix: Restore old behavior of `snapshots --latest <n>` without `--group-by`
+
+Restic 0.19.0 changed the behavior of `snapshots --latest <n>` to no longer
+group snapshots by default.
+
+`snapshots --latest <n>` has been reverted to the old behavior if `--group-by`
+is not specified. When specifying `--group-by`, the output is still grouped as
+requested like in restic 0.19.0.
+
+https://github.com/restic/restic/issues/21869
+https://github.com/restic/restic/pull/21875

cmd/restic/cmd_snapshots.go

@@ -106,7 +106,11 @@ func runSnapshots(ctx context.Context, opts SnapshotOptions, gopts global.Option
 		}
 
 		if opts.Latest > 0 {
-			list = filterLatestSnapshotsInGroup(list, opts.Latest)
+			if grouped {
+				list = filterLatestSnapshotsInGroup(list, opts.Latest)
+			} else {
+				list = filterLatestSnapshots(list, opts.Latest)
+			}
 		}
 		sort.Sort(sort.Reverse(list))
 		snapshotGroups[k] = list
@@ -140,6 +144,43 @@ func runSnapshots(ctx context.Context, opts SnapshotOptions, gopts global.Option
 	return nil
 }
 
+// filterLastSnapshotsKey is used by FilterLastSnapshots.
+type filterLastSnapshotsKey struct {
+	Hostname    string
+	JoinedPaths string
+}
+
+// newFilterLastSnapshotsKey initializes a filterLastSnapshotsKey from a Snapshot
+func newFilterLastSnapshotsKey(sn *data.Snapshot) filterLastSnapshotsKey {
+	// Shallow slice copy
+	var paths = make([]string, len(sn.Paths))
+	copy(paths, sn.Paths)
+	sort.Strings(paths)
+	return filterLastSnapshotsKey{sn.Hostname, strings.Join(paths, "|")}
+}
+
+// filterLatestSnapshots filters a list of snapshots to only return
+// the limit last entries for each hostname and path. If the snapshot
+// contains multiple paths, they will be joined and treated as one
+// item.
+func filterLatestSnapshots(list data.Snapshots, limit int) data.Snapshots {
+	// Sort the snapshots so that the newer ones are listed first
+	sort.SliceStable(list, func(i, j int) bool {
+		return list[i].Time.After(list[j].Time)
+	})
+
+	var results data.Snapshots
+	seen := make(map[filterLastSnapshotsKey]int)
+	for _, sn := range list {
+		key := newFilterLastSnapshotsKey(sn)
+		if seen[key] < limit {
+			seen[key]++
+			results = append(results, sn)
+		}
+	}
+	return results
+}
+
 // filterLatestSnapshotsInGroup filters a list of snapshots to only return
 // the `limit` last entries. It is assumed that the snapshot list only contains
 // one group of snapshots.

cmd/restic/cmd_snapshots_integration_test.go

@@ -35,10 +35,7 @@ func testRunSnapshots(t testing.TB, gopts global.Options) (newest *Snapshot, sna
 	return
 }
 
-func TestSnapshotsGroupByAndLatest(t *testing.T) {
-	env, cleanup := withTestEnvironment(t)
-	defer cleanup()
-
+func snapshotsGroupTestData(t *testing.T, env *testEnvironment, keepPath bool) string {
 	testSetupBackupData(t, env)
 	// two backups on the same host but with different paths
 	opts := BackupOptions{Host: "testhost", TimeStamp: time.Now().Format(time.DateTime)}
@@ -46,9 +43,22 @@ func TestSnapshotsGroupByAndLatest(t *testing.T) {
 	// Use later timestamp for second backup
 	opts.TimeStamp = time.Now().Add(time.Second).Format(time.DateTime)
 	snapshotsIDs := loadSnapshotMap(t, env.gopts)
-	testRunBackup(t, filepath.Dir(env.testdata), []string{"testdata/0"}, opts, env.gopts)
+
+	targets := []string{"testdata/0"}
+	if keepPath {
+		targets = []string{"testdata"}
+	}
+	testRunBackup(t, filepath.Dir(env.testdata), targets, opts, env.gopts)
 	_, secondSnapshotID := lastSnapshot(snapshotsIDs, loadSnapshotMap(t, env.gopts))
 
+	return secondSnapshotID
+}
+
+func TestSnapshotsGroupByAndLatest(t *testing.T) {
+	env, cleanup := withTestEnvironment(t)
+	defer cleanup()
+
+	secondSnapshotID := snapshotsGroupTestData(t, env, false)
 	buf, err := withCaptureStdout(t, env.gopts, func(ctx context.Context, gopts global.Options) error {
 		gopts.JSON = true
 		// only group by host but not path
@@ -65,3 +75,21 @@ func TestSnapshotsGroupByAndLatest(t *testing.T) {
 	rtest.Assert(t, len(snapshots[0].Snapshots) == 1, "expected only one latest snapshot, got %d", len(snapshots[0].Snapshots))
 	rtest.Equals(t, snapshots[0].Snapshots[0].ID.String(), secondSnapshotID, "unexpected snapshot ID")
 }
+
+func TestSnapshotsLatest(t *testing.T) {
+	env, cleanup := withTestEnvironment(t)
+	defer cleanup()
+
+	secondSnapshotID := snapshotsGroupTestData(t, env, true)
+
+	buf, err := withCaptureStdout(t, env.gopts, func(ctx context.Context, gopts global.Options) error {
+		gopts.JSON = true
+		opts := SnapshotOptions{Latest: 1}
+		return runSnapshots(ctx, opts, gopts, []string{}, gopts.Term)
+	})
+	rtest.OK(t, err)
+	snapshots := []Snapshot{}
+	rtest.OK(t, json.Unmarshal(buf.Bytes(), &snapshots))
+	rtest.Assert(t, len(snapshots) == 1, "expected only one snapshot, got %d", len(snapshots))
+	rtest.Equals(t, snapshots[0].ID.String(), secondSnapshotID, "unexpected snapshot ID")
+}