Show commit insertion points during a drag

Render the insertion point of a commit drag as a non-model item in the
commits list. It must be inserted at the right position relative to
the section headers, because the list renderer assumes non-model items
are ordered by their model index.

Not used yet, we'll hook it up to the drag gesture in the next commit.

pkg/gui/context/local_commits_context.go

@@ -2,6 +2,7 @@ package context
 
 import (
 	"log"
+	"slices"
 	"strings"
 	"sync/atomic"
 	"time"
@@ -9,6 +10,7 @@ import (
 	"github.com/jesseduffield/lazygit/pkg/commands/models"
 	"github.com/jesseduffield/lazygit/pkg/gocui"
 	"github.com/jesseduffield/lazygit/pkg/gui/presentation"
+	"github.com/jesseduffield/lazygit/pkg/gui/style"
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
 	"github.com/samber/lo"
 )
@@ -17,6 +19,12 @@ type LocalCommitsContext struct {
 	*LocalCommitsViewModel
 	*ListContextTrait
 	*SearchTrait
+
+	dropIndicator *commitDropIndicator
+}
+
+type commitDropIndicator struct {
+	insertionIndex int
 }
 
 var (
@@ -26,6 +34,7 @@ var (
 )
 
 func NewLocalCommitsContext(c *ContextCommon) *LocalCommitsContext {
+	dropIndicator := &commitDropIndicator{insertionIndex: -1}
 	viewModel := NewLocalCommitsViewModel(
 		func() []*models.Commit { return c.Model().Commits },
 		c,
@@ -94,6 +103,8 @@ func NewLocalCommitsContext(c *ContextCommon) *LocalCommitsContext {
 				})
 			}
 
+			result = addCommitDropIndicator(result, dropIndicator, c.Tr.MoveCommitsHere)
+
 			_, firstRealCommit, found := lo.FindIndexOf(
 				c.Model().Commits, func(c *models.Commit) bool {
 					return !c.IsTODO()
@@ -105,6 +116,8 @@ func NewLocalCommitsContext(c *ContextCommon) *LocalCommitsContext {
 				Index:   firstRealCommit,
 				Content: formatListSectionHeader(c.Tr.CommitsSectionHeader),
 			})
+		} else {
+			result = addCommitDropIndicator(result, dropIndicator, c.Tr.MoveCommitsHere)
 		}
 
 		return result
@@ -113,6 +126,7 @@ func NewLocalCommitsContext(c *ContextCommon) *LocalCommitsContext {
 	ctx := &LocalCommitsContext{
 		LocalCommitsViewModel: viewModel,
 		SearchTrait:           NewSearchTrait(c),
+		dropIndicator:         dropIndicator,
 		ListContextTrait: &ListContextTrait{
 			Context: NewSimpleContext(NewBaseContext(NewBaseContextOpts{
 				View:                        c.Views().Commits,
@@ -137,6 +151,36 @@ func NewLocalCommitsContext(c *ContextCommon) *LocalCommitsContext {
 	return ctx
 }
 
+func addCommitDropIndicator(
+	items []*NonModelItem, indicator *commitDropIndicator, label string,
+) []*NonModelItem {
+	if indicator.insertionIndex < 0 {
+		return items
+	}
+
+	insertAt := len(items)
+	for i, item := range items {
+		if item.Index > indicator.insertionIndex {
+			insertAt = i
+			break
+		}
+	}
+
+	return slices.Insert(items, insertAt, &NonModelItem{
+		Index:   indicator.insertionIndex,
+		Content: style.FgCyan.SetBold().Sprintf("━━━━━━ %s ━━━━━━", label),
+		Column:  6, // align with the commit subject
+	})
+}
+
+func (self *LocalCommitsContext) SetDropInsertionIndex(index int) {
+	self.dropIndicator.insertionIndex = index
+}
+
+func (self *LocalCommitsContext) ClearDropInsertionIndex() {
+	self.dropIndicator.insertionIndex = -1
+}
+
 type LocalCommitsViewModel struct {
 	*ListViewModel[*models.Commit]
 

pkg/gui/context/local_commits_context_test.go

@@ -0,0 +1,29 @@
+package context
+
+import (
+	"testing"
+
+	"github.com/jesseduffield/lazygit/pkg/gui/style"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestAddCommitDropIndicator(t *testing.T) {
+	pendingHeader := &NonModelItem{Index: 0, Content: "pending"}
+	commitsHeader := &NonModelItem{Index: 3, Content: "commits"}
+	indicator := &commitDropIndicator{insertionIndex: 3}
+
+	items := addCommitDropIndicator([]*NonModelItem{pendingHeader}, indicator, "drop here")
+	items = append(items, commitsHeader)
+
+	assert.Equal(t, []*NonModelItem{
+		pendingHeader,
+		{
+			Index:   3,
+			Content: style.FgCyan.SetBold().Sprint("━━━━━━ drop here ━━━━━━"),
+			Column:  6,
+		},
+		commitsHeader,
+	}, items)
+	assert.Equal(t, 6, modelIndexToViewIndex(4, items, 3))
+	assert.Equal(t, 3, viewIndexToModelIndex(4, items, 4))
+}

pkg/i18n/english.go

@@ -373,6 +373,7 @@ type TranslationSet struct {
 	PendingCherryPicksSectionHeader       string
 	PendingRevertsSectionHeader           string
 	CommitsSectionHeader                  string
+	MoveCommitsHere                       string
 	YouDied                               string
 	RewordNotSupported                    string
 	ChangingThisActionIsNotAllowed        string
@@ -1523,6 +1524,7 @@ func EnglishTranslationSet() *TranslationSet {
 		PendingCherryPicksSectionHeader:      "Pending cherry-picks",
 		PendingRevertsSectionHeader:          "Pending reverts",
 		CommitsSectionHeader:                 "Commits",
+		MoveCommitsHere:                      "drop here",
 		YouDied:                              "YOU DIED!",
 		RewordNotSupported:                   "Rewording commits while interactively rebasing is not currently supported",
 		ChangingThisActionIsNotAllowed:       "Changing this kind of rebase todo entry is not allowed",