Dim the divergence of a branch whose upstream was rewritten

When somebody else rebases a branch and force-pushes it, our branch
shows up as diverged, say ↓5↑3, and that looks exactly like a branch
that carries three commits of our own. The two want different treatment.
The first one only has to be moved to its upstream, while the second one
needs a decision about what to do with those commits. The panel doesn't
tell them apart, so users have to look at each branch in turn to find
out which one they are dealing with.

Determine for every diverged branch whether it has commits of its own,
and dim its divergence when it doesn't. This runs on a worker, as it
takes a few git commands per diverged branch, and a branch keeps the
answer from the previous load while a new one is in flight, so that the
display doesn't flicker. A later commit teaches the fast-forward command
to act on such a branch.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

pkg/commands/git.go

@@ -145,7 +145,7 @@ func NewGitCommandAux(
 	gitHubCommands := git_commands.NewGitHubCommands(gitCommon)
 	hostingServiceCommands := git_commands.NewHostingServiceCommand(gitCommon)
 
-	branchLoader := git_commands.NewBranchLoader(cmn, gitCommon, cmd, branchCommands.CurrentBranchInfo, configCommands)
+	branchLoader := git_commands.NewBranchLoader(cmn, gitCommon, cmd, branchCommands.CurrentBranchInfo, branchCommands.HasLocalOnlyCommits, configCommands)
 	commitFileLoader := git_commands.NewCommitFileLoader(cmn, cmd)
 	commitLoader := git_commands.NewCommitLoader(cmn, cmd, statusCommands.WorkingTreeState, gitCommon)
 	reflogCommitLoader := git_commands.NewReflogCommitLoader(cmn, cmd)

pkg/commands/git_commands/branch_loader.go

@@ -44,6 +44,7 @@ type BranchLoader struct {
 	*GitCommon
 	cmd                  oscommands.ICmdObjBuilder
 	getCurrentBranchInfo func() (BranchInfo, error)
+	hasLocalOnlyCommits  func(*models.Branch) (bool, error)
 	config               BranchLoaderConfigCommands
 }
 
@@ -52,6 +53,7 @@ func NewBranchLoader(
 	gitCommon *GitCommon,
 	cmd oscommands.ICmdObjBuilder,
 	getCurrentBranchInfo func() (BranchInfo, error),
+	hasLocalOnlyCommits func(*models.Branch) (bool, error),
 	config BranchLoaderConfigCommands,
 ) *BranchLoader {
 	return &BranchLoader{
@@ -59,6 +61,7 @@ func NewBranchLoader(
 		GitCommon:            gitCommon,
 		cmd:                  cmd,
 		getCurrentBranchInfo: getCurrentBranchInfo,
+		hasLocalOnlyCommits:  hasLocalOnlyCommits,
 		config:               config,
 	}
 }
@@ -135,24 +138,63 @@ func (self *BranchLoader) Load(reflogCommits []*models.Commit,
 			branch.UpstreamBranch = match.Merge
 		}
 
-		// If the branch already existed, take over its BehindBaseBranch value
-		// to reduce flicker
+		// If the branch already existed, take over the values that are
+		// determined in the background, to reduce flicker
 		if oldBranch, found := lo.Find(oldBranches, func(b *models.Branch) bool {
 			return b.Name == branch.Name
 		}); found {
 			branch.BehindBaseBranch.Store(oldBranch.BehindBaseBranch.Load())
+			branch.UpstreamRewritten.Store(oldBranch.UpstreamRewritten.Load())
 		}
 	}
 
-	if loadExtraInfo && self.UserConfig().Gui.ShowDivergenceFromBaseBranch != "none" {
+	if loadExtraInfo {
+		if self.UserConfig().Gui.ShowDivergenceFromBaseBranch != "none" {
+			onWorker(func() error {
+				return self.GetBehindBaseBranchValuesForAllBranches(branches, mainBranches, renderFunc)
+			})
+		}
+
 		onWorker(func() error {
-			return self.GetBehindBaseBranchValuesForAllBranches(branches, mainBranches, renderFunc)
+			return self.checkForRewrittenUpstreams(branches, renderFunc)
 		})
 	}
 
 	return branches, nil
 }
 
+// For each branch that has diverged from its upstream, determines whether the
+// divergence comes from the upstream branch having been rewritten, and stores
+// the answer in the branch. A branch that we can't determine it for keeps the
+// answer "no", so that we don't offer anything we aren't sure about.
+func (self *BranchLoader) checkForRewrittenUpstreams(branches []*models.Branch, renderFunc func()) error {
+	t := time.Now()
+	errg := errgroup.Group{}
+
+	for _, branch := range branches {
+		if !branch.IsAheadForPull() || !branch.IsBehindForPull() {
+			branch.UpstreamRewritten.Store(false)
+			continue
+		}
+
+		errg.Go(func() error {
+			hasLocalOnlyCommits, err := self.hasLocalOnlyCommits(branch)
+			if err != nil {
+				// Not worth bothering the user about; it only means that we
+				// don't show this branch differently.
+				self.Log.Errorf("Failed to check whether branch %s has commits of its own: %v", branch.Name, err)
+			}
+			branch.UpstreamRewritten.Store(err == nil && !hasLocalOnlyCommits)
+			return nil
+		})
+	}
+
+	err := errg.Wait()
+	self.Log.Debugf("time to check for rewritten upstreams for all branches: %s", time.Since(t))
+	renderFunc()
+	return err
+}
+
 func (self *BranchLoader) GetBehindBaseBranchValuesForAllBranches(
 	branches []*models.Branch,
 	mainBranches *MainBranches,

pkg/commands/git_commands/branch_loader_test.go

@@ -6,8 +6,10 @@ import (
 	"testing"
 	"time"
 
+	"github.com/go-errors/errors"
 	"github.com/jesseduffield/lazygit/pkg/commands/models"
 	"github.com/jesseduffield/lazygit/pkg/commands/oscommands"
+	"github.com/sasha-s/go-deadlock"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -291,3 +293,62 @@ func TestGetBehindBaseBranchValuesForAllBranches_LegacyPath(t *testing.T) {
 
 	runner.CheckForMissingCalls()
 }
+
+func TestCheckForRewrittenUpstreams(t *testing.T) {
+	branch := func(name string, ahead string, behind string) *models.Branch {
+		return &models.Branch{
+			Name:           name,
+			UpstreamRemote: "origin",
+			UpstreamBranch: name,
+			AheadForPull:   ahead,
+			BehindForPull:  behind,
+		}
+	}
+
+	notDiverged := branch("not-diverged", "0", "2")
+	rewritten := branch("rewritten", "3", "5")
+	ownCommits := branch("own-commits", "3", "5")
+	failing := branch("failing", "1", "1")
+
+	// A branch that is no longer diverged must lose the value it had before
+	notDiverged.UpstreamRewritten.Store(true)
+
+	branches := []*models.Branch{notDiverged, rewritten, ownCommits, failing}
+
+	var mutex deadlock.Mutex
+	queried := []string{}
+	hasLocalOnlyCommits := func(branch *models.Branch) (bool, error) {
+		mutex.Lock()
+		queried = append(queried, branch.Name)
+		mutex.Unlock()
+
+		switch branch.Name {
+		case "own-commits":
+			return true, nil
+		case "failing":
+			return false, errors.New("error")
+		default:
+			return false, nil
+		}
+	}
+
+	gitCommon := buildGitCommon(commonDeps{})
+	loader := &BranchLoader{
+		Common:              gitCommon.Common,
+		GitCommon:           gitCommon,
+		cmd:                 gitCommon.cmd,
+		hasLocalOnlyCommits: hasLocalOnlyCommits,
+	}
+
+	rendered := false
+	err := loader.checkForRewrittenUpstreams(branches, func() { rendered = true })
+	assert.NoError(t, err)
+	assert.True(t, rendered, "renderFunc should have been called")
+
+	assert.ElementsMatch(t, []string{"rewritten", "own-commits", "failing"}, queried,
+		"only diverged branches should be looked at")
+	assert.False(t, notDiverged.UpstreamRewritten.Load())
+	assert.True(t, rewritten.UpstreamRewritten.Load())
+	assert.False(t, ownCommits.UpstreamRewritten.Load())
+	assert.False(t, failing.UpstreamRewritten.Load(), "a failed check should not claim anything")
+}

pkg/commands/models/branch.go

@@ -47,6 +47,13 @@ type Branch struct {
 	// determined yet, or up to date with base branch. (We don't need to
 	// distinguish the two, as we don't draw anything in both cases.)
 	BehindBaseBranch atomic.Int32
+
+	// Whether the branch has diverged from its upstream because the upstream
+	// branch was rewritten, and not because the branch has commits of its own.
+	// Such a branch can be reset to its upstream without losing anything.
+	// False for branches that haven't diverged, and for those we haven't
+	// determined it for yet.
+	UpstreamRewritten atomic.Bool
 }
 
 func (b *Branch) FullRefName() string {

pkg/gui/presentation/branches.go

@@ -26,6 +26,8 @@ type branchColorPattern struct {
 
 var branchColorPatterns []branchColorPattern
 
+var dimYellow = style.FgYellow.SetDim()
+
 func GetBranchListDisplayStrings(
 	branches []*models.Branch,
 	getItemOperation func(item types.HasUrn) types.ItemOperation,
@@ -223,7 +225,12 @@ func BranchStatus(
 		} else if branch.RemoteBranchNotStoredLocally() {
 			result = style.FgMagenta.Sprint("?")
 		} else if branch.IsBehindForPull() && branch.IsAheadForPull() {
-			result = style.FgYellow.Sprintf("↓%s↑%s", branch.BehindForPull, branch.AheadForPull)
+			// A branch that diverged only because its upstream was rewritten
+			// has no commits of its own, and fast-forwarding it resolves the
+			// divergence. Dim it to set it apart from a branch whose
+			// divergence needs a decision.
+			divergenceStyle := lo.Ternary(branch.UpstreamRewritten.Load(), dimYellow, style.FgYellow)
+			result = divergenceStyle.Sprintf("↓%s↑%s", branch.BehindForPull, branch.AheadForPull)
 		} else if branch.IsBehindForPull() {
 			result = style.FgYellow.Sprintf("↓%s", branch.BehindForPull)
 		} else if branch.IsAheadForPull() {

pkg/gui/presentation/branches_test.go

@@ -457,3 +457,30 @@ func TestGetBranchTextStyle(t *testing.T) {
 	SetCustomBranches(patterns)
 	assert.Equal(t, style.FgRed, GetBranchTextStyle("feature/ISSUE-1"))
 }
+
+func TestBranchStatus(t *testing.T) {
+	oldColorLevel := color.ForceSetColorLevel(terminfo.ColorLevelMillions)
+	defer color.ForceSetColorLevel(oldColorLevel)
+
+	c := common.NewDummyCommon()
+
+	divergedBranch := func(upstreamRewritten bool) *models.Branch {
+		branch := &models.Branch{
+			Name:           "branch",
+			UpstreamRemote: "origin",
+			UpstreamBranch: "branch",
+			AheadForPull:   "3",
+			BehindForPull:  "5",
+		}
+		branch.UpstreamRewritten.Store(upstreamRewritten)
+		return branch
+	}
+
+	status := func(branch *models.Branch) string {
+		return BranchStatus(branch, types.ItemOperationNone, c.Tr, time.Time{}, c.UserConfig())
+	}
+
+	assert.Equal(t, "\x1b[33m↓5↑3\x1b[0m", status(divergedBranch(false)))
+	assert.Equal(t, "\x1b[33;2m↓5↑3\x1b[0m", status(divergedBranch(true)),
+		"a branch whose upstream was rewritten should be dimmed")
+}