Fixed --track when used with --tac

Fix #3234

5 files changed, 30 insertions, 14 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4c16db6a..ec087b0a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,7 +3,9 @@ CHANGELOG
 
 0.39.1
 ------
-- Disallow using `--track` with `--tac` as the result can be very confusing
+- Fixed `--track` behavior when used with `--tac`
+    - However, using `--track` with `--tac` is not recommended. The resulting
+      behavior can be very confusing.
 - Bug fixes and improvements
 
 0.39.0
diff --git a/man/man1/fzf.1 b/man/man1/fzf.1
index d632a4ce..4bb29bc4 100644
--- a/man/man1/fzf.1
+++ b/man/man1/fzf.1
@@ -95,7 +95,6 @@ Do not sort the result
 .B "--track"
 Make fzf track the current selection when the result list is updated.
 This can be useful when browsing logs using fzf with sorting disabled.
-This option is not compatible with \fB--tac\fR.
 
 .RS
 e.g.
diff --git a/src/merger.go b/src/merger.go
index cdf00acc..5c12575c 100644
--- a/src/merger.go
+++ b/src/merger.go
@@ -60,17 +60,30 @@ func (mg *Merger) Length() int {
 	return mg.count
 }
 
+func (mg *Merger) First() Result {
+	if mg.tac && !mg.sorted {
+		return mg.Get(mg.count - 1)
+	}
+	return mg.Get(0)
+}
+
 // FindIndex returns the index of the item with the given item index
 func (mg *Merger) FindIndex(itemIndex int32) int {
+	index := -1
 	if mg.pass {
-		return int(itemIndex)
-	}
-	for i := 0; i < mg.count; i++ {
-		if mg.Get(i).item.Index() == itemIndex {
-			return i
+		index = int(itemIndex)
+		if mg.tac {
+			index = mg.count - index - 1
+		}
+	} else {
+		for i := 0; i < mg.count; i++ {
+			if mg.Get(i).item.Index() == itemIndex {
+				index = i
+				break
+			}
 		}
 	}
-	return -1
+	return index
 }
 
 // Get returns the pointer to the Result object indexed by the given integer
diff --git a/src/options.go b/src/options.go
index 071819d9..e09e9b59 100644
--- a/src/options.go
+++ b/src/options.go
@@ -1083,6 +1083,8 @@ func parseActionList(masked string, original string, prevActions []*action, putA
 			appendAction(actToggleAll)
 		case "toggle-search":
 			appendAction(actToggleSearch)
+		case "toggle-track":
+			appendAction(actToggleTrack)
 		case "select":
 			appendAction(actSelect)
 		case "select-all":
@@ -1938,10 +1940,6 @@ func postProcessOptions(opts *Options) {
 		errorExit("scrollbar display width should be 1")
 	}
 
-	if opts.Track && opts.Tac {
-		errorExit("--track cannot be used with --tac")
-	}
-
 	// Default actions for CTRL-N / CTRL-P when --history is set
 	if opts.History != nil {
 		if _, prs := opts.Keymap[tui.CtrlP.AsEvent()]; !prs {
diff --git a/src/terminal.go b/src/terminal.go
index 5ecba97b..cbbde9c5 100644
--- a/src/terminal.go
+++ b/src/terminal.go
@@ -907,8 +907,12 @@ func (t *Terminal) UpdateProgress(progress float32) {
 func (t *Terminal) UpdateList(merger *Merger, reset bool) {
 	t.mutex.Lock()
 	var prevIndex int32 = -1
-	if !reset && t.track && t.merger.Length() > 0 {
-		prevIndex = t.merger.Get(t.cy).item.Index()
+	if !reset && t.track {
+		if t.merger.Length() > 0 {
+			prevIndex = t.merger.Get(t.cy).item.Index()
+		} else if merger.Length() > 0 {
+			prevIndex = merger.First().item.Index()
+		}
 	}
 	t.progress = 100
 	t.merger = merger