add program version to snapshot

changelog/unreleased/issue-4188

@@ -0,0 +1,7 @@
+Enhancement: Include client version in snapshot metadata
+
+The client version number is now included in the `program_version` field of a snapshot.
+It can be inspected by using either `restic cat snapshot snapshotID` or `restic snapshots --json`.
+
+https://github.com/restic/restic/issues/4188
+https://github.com/restic/restic/pull/4378

cmd/restic/cmd_backup.go

@@ -645,6 +645,7 @@ func runBackup(ctx context.Context, opts BackupOptions, gopts GlobalOptions, ter
 		Time:           timeStamp,
 		Hostname:       opts.Host,
 		ParentSnapshot: parentSnapshot,
+		ProgramVersion: "restic " + version,
 	}
 
 	if !gopts.JSON {

internal/archiver/archiver.go

@@ -680,6 +680,7 @@ type SnapshotOptions struct {
 	Excludes       []string
 	Time           time.Time
 	ParentSnapshot *restic.Snapshot
+	ProgramVersion string
 }
 
 // loadParentTree loads a tree referenced by snapshot id. If id is null, nil is returned.
@@ -796,6 +797,7 @@ func (arch *Archiver) Snapshot(ctx context.Context, targets []string, opts Snaps
 		return nil, restic.ID{}, err
 	}
 
+	sn.ProgramVersion = opts.ProgramVersion
 	sn.Excludes = opts.Excludes
 	if opts.ParentSnapshot != nil {
 		sn.Parent = opts.ParentSnapshot.ID()

internal/restic/snapshot.go

@@ -25,6 +25,8 @@ type Snapshot struct {
 	Tags     []string  `json:"tags,omitempty"`
 	Original *ID       `json:"original,omitempty"`
 
+	ProgramVersion string `json:"program_version,omitempty"`
+
 	id *ID // plaintext ID, used during restore
 }