add new snap switch command

client/snap_op.go

@@ -116,6 +116,11 @@ func (client *Client) Revert(name string, options *SnapOptions) (changeID string
 	return client.doSnapAction("revert", name, options)
 }
 
+// Switch moves the snap to a different channel without a refresh
+func (client *Client) Switch(name string, options *SnapOptions) (changeID string, err error) {
+	return client.doSnapAction("switch", name, options)
+}
+
 var ErrDangerousNotApplicable = fmt.Errorf("dangerous option only meaningful when installing from a local file")
 
 func (client *Client) doSnapAction(actionName string, snapName string, options *SnapOptions) (changeID string, err error) {

cmd/snap/cmd_snap_op.go

@@ -820,6 +820,42 @@ func (x *cmdRevert) Execute(args []string) error {
 	return nil
 }
 
+var shortSwitchHelp = i18n.G("Switch snap to a different channel")
+var longSwitchHelp = i18n.G(`
+The switch command switch the given snap to a different channel without
+actually doing a refresh.
+`)
+
+type cmdSwitch struct {
+	channelMixin
+
+	Positional struct {
+		Snap    installedSnapName `positional-arg-name:"<snap>" required:"1"`
+		Channel string            `positional-arg-name:"<channel>" required:"1"`
+	} `positional-args:"yes" required:"yes"`
+}
+
+func (x cmdSwitch) Execute(args []string) error {
+	cli := Client()
+	name := string(x.Positional.Snap)
+	channel := string(x.Positional.Channel)
+	opts := &client.SnapOptions{
+		Channel: channel,
+	}
+	changeID, err := cli.Switch(name, opts)
+	if err != nil {
+		return err
+	}
+
+	_, err = wait(cli, changeID)
+	if err != nil {
+		return err
+	}
+
+	fmt.Fprintf(Stdout, i18n.G("%s switched to %s\n"), name, channel)
+	return nil
+}
+
 func init() {
 	addCommand("remove", shortRemoveHelp, longRemoveHelp, func() flags.Commander { return &cmdRemove{} },
 		map[string]string{"revision": i18n.G("Remove only the given revision")}, nil)
@@ -841,4 +877,6 @@ func init() {
 	addCommand("revert", shortRevertHelp, longRevertHelp, func() flags.Commander { return &cmdRevert{} }, modeDescs.also(map[string]string{
 		"revision": "Revert to the given revision",
 	}), nil)
+	addCommand("switch", shortSwitchHelp, longSwitchHelp, func() flags.Commander { return &cmdSwitch{} }, nil, nil)
+
 }

daemon/api.go

@@ -758,6 +758,7 @@ var (
 	snapstateRemoveMany        = snapstate.RemoveMany
 	snapstateRevert            = snapstate.Revert
 	snapstateRevertToRevision  = snapstate.RevertToRevision
+	snapstateSwitch            = snapstate.Switch
 
 	assertstateRefreshSnapDeclarations = assertstate.RefreshSnapDeclarations
 )
@@ -1009,6 +1010,19 @@ func snapDisable(inst *snapInstruction, st *state.State) (string, []*state.TaskS
 	return msg, []*state.TaskSet{ts}, nil
 }
 
+func snapSwitch(inst *snapInstruction, st *state.State) (string, []*state.TaskSet, error) {
+	if !inst.Revision.Unset() {
+		return "", nil, errors.New("switch takes no revision")
+	}
+	ts, err := snapstate.Switch(st, inst.Snaps[0], inst.Channel)
+	if err != nil {
+		return "", nil, err
+	}
+
+	msg := fmt.Sprintf(i18n.G("Switch %q snap to %s"), inst.Snaps[0], inst.Channel)
+	return msg, []*state.TaskSet{ts}, nil
+}
+
 type snapActionFunc func(*snapInstruction, *state.State) (string, []*state.TaskSet, error)
 
 var snapInstructionDispTable = map[string]snapActionFunc{
@@ -1018,6 +1032,7 @@ var snapInstructionDispTable = map[string]snapActionFunc{
 	"revert":  snapRevert,
 	"enable":  snapEnable,
 	"disable": snapDisable,
+	"switch":  snapSwitch,
 }
 
 func (inst *snapInstruction) dispatch() snapActionFunc {

daemon/api_test.go

@@ -495,6 +495,7 @@ func (s *apiSuite) TestListIncludesAll(c *check.C) {
 		"snapstateRefreshCandidates",
 		"snapstateRevert",
 		"snapstateRevertToRevision",
+		"snapstateSwitch",
 		"assertstateRefreshSnapDeclarations",
 		"unsafeReadSnapInfo",
 		"osutilAddUser",

overlord/snapstate/snapmgr.go

@@ -394,6 +394,9 @@ func Manager(st *state.State) (*SnapManager, error) {
 	runner.AddHandler("setup-aliases", m.doSetupAliases, m.undoSetupAliases)
 	runner.AddHandler("remove-aliases", m.doRemoveAliases, m.doSetupAliases)
 
+	// misc
+	runner.AddHandler("switch-snap", m.doSwitchSnap, nil)
+
 	// control serialisation
 	runner.SetBlocked(m.blockedTask)
 
@@ -994,9 +997,23 @@ func (m *SnapManager) doCopySnapData(t *state.Task, _ *tomb.Tomb) error {
 	return m.backend.CopySnapData(newInfo, oldInfo, pb)
 }
 
-func (m *SnapManager) doLinkSnap(t *state.Task, _ *tomb.Tomb) error {
+func (m *SnapManager) doSwitchSnap(t *state.Task, _ *tomb.Tomb) error {
 	st := t.State()
+	st.Lock()
+	defer st.Unlock()
 
+	snapsup, snapst, err := snapSetupAndState(t)
+	if err != nil {
+		return err
+	}
+	snapst.Channel = snapsup.Channel
+
+	Set(st, snapsup.Name(), snapst)
+	return nil
+}
+
+func (m *SnapManager) doLinkSnap(t *state.Task, _ *tomb.Tomb) error {
+	st := t.State()
 	st.Lock()
 	defer st.Unlock()
 

overlord/snapstate/snapstate.go

@@ -674,6 +674,28 @@ func autoAliasesUpdate(st *state.State, names []string, updates []*snap.Info) (n
 	return new, mustRetire, transferTargets, nil
 }
 
+// Switch switches a snap to a new channel
+func Switch(st *state.State, name, channel string) (*state.TaskSet, error) {
+	var snapst SnapState
+	err := Get(st, name, &snapst)
+	if err != nil && err != state.ErrNoState {
+		return nil, err
+	}
+	if !snapst.HasCurrent() {
+		return nil, fmt.Errorf("cannot find snap %q", name)
+	}
+
+	snapsup := &SnapSetup{
+		SideInfo: snapst.CurrentSideInfo(),
+		Channel:  channel,
+	}
+
+	switchSnap := st.NewTask("switch-snap", fmt.Sprintf(i18n.G("Switch snap %q to %s"), snapsup.Name(), snapsup.Channel))
+	switchSnap.Set("snap-setup", &snapsup)
+
+	return state.NewTaskSet(switchSnap), nil
+}
+
 // Update initiates a change updating a snap.
 // Note that the state must be locked by the caller.
 func Update(st *state.State, name, channel string, revision snap.Revision, userID int, flags Flags) (*state.TaskSet, error) {

tests/main/snap-switch/task.yaml

@@ -0,0 +1,8 @@
+summary: Ensure that the snap switch command works
+
+execute: |
+    snap install test-snapd-tools
+    snap info test-snapd-tools|MATCH "tracking: +stable"
+
+    snap switch test-snapd-tools edge
+    snap info test-snapd-tools|MATCH "tracking: +edge"