Notify user of noteworthy lineage changes

features/kill/current_branch/features/parent_branch.feature

@@ -22,6 +22,10 @@ Feature: delete a branch within a branch chain
       |        | git commit -m "WIP on beta" |
       |        | git checkout alpha          |
       | alpha  | git branch -D beta          |
+    And it prints:
+      """
+      branch "gamma" is now a child of "alpha"
+      """
     And the current branch is now "alpha"
     And no uncommitted files exist
     And the branches are now

features/ship/current_branch/features/parent_branch.feature

@@ -23,6 +23,10 @@ Feature: ship a parent branch
       |        | git commit -m "parent done"       |
       |        | git push                          |
       |        | git branch -D parent              |
+    And it prints:
+      """
+      branch "child" is now a child of "main"
+      """
     And the current branch is now "main"
     And now these commits exist
       | BRANCH | LOCATION      | MESSAGE       |

src/cmd/append.go

@@ -181,7 +181,7 @@ func appendSteps(config *appendConfig) steps.List {
 		})
 	}
 	list.Add(&step.CreateBranch{Branch: config.targetBranch, StartingPoint: config.parentBranch.Location()})
-	list.Add(&step.SetParent{Branch: config.targetBranch, ParentBranch: config.parentBranch})
+	list.Add(&step.SetParent{Branch: config.targetBranch, Parent: config.parentBranch})
 	list.Add(&step.Checkout{Branch: config.targetBranch})
 	if config.remotes.HasOrigin() && config.shouldNewBranchPush && !config.isOffline {
 		list.Add(&step.CreateTrackingBranch{Branch: config.targetBranch, NoPushHook: !config.pushHook})

src/cmd/kill.go

@@ -198,7 +198,7 @@ func killFeatureBranch(list *steps.List, finalUndoList *steps.List, config killC
 func removeBranchFromLineage(args removeBranchFromLineageArgs) {
 	childBranches := args.lineage.Children(args.branch)
 	for _, child := range childBranches {
-		args.list.Add(&step.SetParent{Branch: child, ParentBranch: args.parent})
+		args.list.Add(&step.ChangeParent{Branch: child, Parent: args.parent})
 	}
 	args.list.Add(&step.DeleteParentBranch{Branch: args.branch})
 }

src/cmd/prepend.go

@@ -182,8 +182,8 @@ func prependSteps(config *prependConfig) steps.List {
 		})
 	}
 	list.Add(&step.CreateBranch{Branch: config.targetBranch, StartingPoint: config.parentBranch.Location()})
-	list.Add(&step.SetParent{Branch: config.targetBranch, ParentBranch: config.parentBranch})
-	list.Add(&step.SetParent{Branch: config.branches.Initial, ParentBranch: config.targetBranch})
+	list.Add(&step.SetParent{Branch: config.targetBranch, Parent: config.parentBranch})
+	list.Add(&step.SetParent{Branch: config.branches.Initial, Parent: config.targetBranch})
 	list.Add(&step.Checkout{Branch: config.targetBranch})
 	if config.remotes.HasOrigin() && config.shouldNewBranchPush && !config.isOffline {
 		list.Add(&step.CreateTrackingBranch{Branch: config.targetBranch, NoPushHook: !config.pushHook})

src/cmd/rename_branch.go

@@ -175,10 +175,10 @@ func renameBranchSteps(config *renameBranchConfig) steps.List {
 	} else {
 		lineage := config.lineage
 		result.Add(&step.DeleteParentBranch{Branch: config.oldBranch.LocalName})
-		result.Add(&step.SetParent{Branch: config.newBranch, ParentBranch: lineage.Parent(config.oldBranch.LocalName)})
+		result.Add(&step.SetParent{Branch: config.newBranch, Parent: lineage.Parent(config.oldBranch.LocalName)})
 	}
 	for _, child := range config.lineage.Children(config.oldBranch.LocalName) {
-		result.Add(&step.SetParent{Branch: child, ParentBranch: config.newBranch})
+		result.Add(&step.SetParent{Branch: child, Parent: config.newBranch})
 	}
 	if config.oldBranch.HasTrackingBranch() && !config.isOffline {
 		result.Add(&step.CreateTrackingBranch{Branch: config.newBranch, NoPushHook: config.noPushHook})

src/cmd/ship.go

@@ -364,7 +364,7 @@ func shipSteps(config *shipConfig, commitMessage string) steps.List {
 	list.Add(&step.DeleteLocalBranch{Branch: config.branchToShip.LocalName, Parent: config.mainBranch.Location(), Force: false})
 	list.Add(&step.DeleteParentBranch{Branch: config.branchToShip.LocalName})
 	for _, child := range config.childBranches {
-		list.Add(&step.SetParent{Branch: child, ParentBranch: config.targetBranch.LocalName})
+		list.Add(&step.ChangeParent{Branch: child, Parent: config.targetBranch.LocalName})
 	}
 	if !config.isShippingInitialBranch {
 		list.Add(&step.Checkout{Branch: config.branches.Initial})

src/messages/en.go

@@ -16,6 +16,7 @@ const (
 	BranchHasWrongSHA                 = "cannot reset branch %q to %q because it received additional commits in the meantime. It should have SHA %q but has %q"
 	BranchLocalSHAProblem             = "cannot determine SHA of local branch %q: %w"
 	BranchLocalProblem                = "cannot determine whether the local branch %q exists: %w"
+	BranchParentChanged               = "branch %q is now a child of %q"
 	BrowserOpen                       = "Please open in a browser: %s\n"
 	CacheUnitialized                  = "using a cached value before initialization"
 	CommandsRun                       = "Ran %d shell commands."

src/persistence/save_load_test.go

@@ -43,6 +43,10 @@ func TestLoadSave(t *testing.T) {
 					&step.AbortMerge{},
 					&step.AbortRebase{},
 					&step.AddToPerennialBranches{Branch: domain.NewLocalBranchName("branch")},
+					&step.ChangeParent{
+						Branch: domain.NewLocalBranchName("branch"),
+						Parent: domain.NewLocalBranchName("parent"),
+					},
 					&step.Checkout{Branch: domain.NewLocalBranchName("branch")},
 					&step.CommitOpenChanges{},
 					&step.ConnectorMergeProposal{
@@ -132,8 +136,8 @@ func TestLoadSave(t *testing.T) {
 						Value: "1",
 					},
 					&step.SetParent{
-						Branch:       domain.NewLocalBranchName("branch"),
-						ParentBranch: domain.NewLocalBranchName("parent"),
+						Branch: domain.NewLocalBranchName("branch"),
+						Parent: domain.NewLocalBranchName("parent"),
 					},
 					&step.SkipCurrentBranch{},
 					&step.SquashMerge{
@@ -179,6 +183,13 @@ func TestLoadSave(t *testing.T) {
       },
       "type": "AddToPerennialBranches"
     },
+    {
+      "data": {
+        "Branch": "branch",
+        "Parent": "parent"
+      },
+      "type": "ChangeParent"
+    },
     {
       "data": {
         "Branch": "branch"
@@ -371,7 +382,7 @@ func TestLoadSave(t *testing.T) {
     {
       "data": {
         "Branch": "branch",
-        "ParentBranch": "parent"
+        "Parent": "parent"
       },
       "type": "SetParent"
     },

src/step/change_parent.go

@@ -0,0 +1,25 @@
+package step
+
+import (
+	"fmt"
+
+	"github.com/git-town/git-town/v9/src/domain"
+	"github.com/git-town/git-town/v9/src/messages"
+)
+
+// ChangeParent changes the parent of the given branch to the given parent.
+// Use SetParent to set the parent if no parent existed before.
+type ChangeParent struct {
+	Branch domain.LocalBranchName
+	Parent domain.LocalBranchName
+	Empty
+}
+
+func (step *ChangeParent) Run(args RunArgs) error {
+	err := args.Runner.Config.SetParent(step.Branch, step.Parent)
+	if err != nil {
+		return err
+	}
+	args.Runner.FinalMessages.Add(fmt.Sprintf(messages.BranchParentChanged, step.Branch, step.Parent))
+	return nil
+}

src/step/set_parent.go

@@ -0,0 +1,19 @@
+package step
+
+import "github.com/git-town/git-town/v9/src/domain"
+
+// SetParent sets the given parent branch as the parent of the given branch.
+// Use ChangeParent to change an existing parent.
+type SetParent struct {
+	Branch domain.LocalBranchName
+	Parent domain.LocalBranchName
+	Empty
+}
+
+func (step *SetParent) Run(args RunArgs) error {
+	err := args.Runner.Config.SetParent(step.Branch, step.Parent)
+	if err != nil {
+		return err
+	}
+	return nil
+}

src/steps/json.go

@@ -49,6 +49,8 @@ func DetermineStep(stepType string) step.Step { //nolint:ireturn
 		return &step.AbortRebase{}
 	case "AddToPerennialBranches":
 		return &step.AddToPerennialBranches{}
+	case "ChangeParent":
+		return &step.ChangeParent{}
 	case "Checkout":
 		return &step.Checkout{}
 	case "CheckoutIfExists":