WIP

toggle-flow.patch

diff --git a/src/options.go b/src/options.go
index 962e516..6519d08 100644
--- a/src/options.go
+++ b/src/options.go
@@ -91,42 +91,43 @@ func defaultMargin() [4]string {
 
 // Options stores the values of command-line options
 type Options struct {
-	Fuzzy       bool
-	Extended    bool
-	Case        Case
-	Nth         []Range
-	WithNth     []Range
-	Delimiter   Delimiter
-	Sort        int
-	Tac         bool
-	Criteria    []criterion
-	Multi       bool
-	Ansi        bool
-	Mouse       bool
-	Theme       *curses.ColorTheme
-	Black       bool
-	Reverse     bool
-	Cycle       bool
-	Hscroll     bool
-	InlineInfo  bool
-	Prompt      string
-	Query       string
-	Select1     bool
-	Exit0       bool
-	Filter      *string
-	ToggleSort  bool
-	Expect      map[int]string
-	Keymap      map[int]actionType
-	Execmap     map[int]string
-	PrintQuery  bool
-	ReadZero    bool
-	Sync        bool
-	History     *History
-	Header      []string
-	HeaderLines int
-	Margin      [4]string
-	Tabstop     int
-	Version     bool
+	Fuzzy        bool
+	Extended     bool
+	Case         Case
+	Nth          []Range
+	WithNth      []Range
+	Delimiter    Delimiter
+	Sort         int
+	Tac          bool
+	Criteria     []criterion
+	Multi        bool
+	Ansi         bool
+	Mouse        bool
+	Theme        *curses.ColorTheme
+	Black        bool
+	Reverse      bool
+	Cycle        bool
+	Hscroll      bool
+	InlineInfo   bool
+	Prompt       string
+	Query        string
+	Select1      bool
+	Exit0        bool
+	Filter       *string
+	ToggleSort   bool
+	ToggleFollow bool
+	Expect       map[int]string
+	Keymap       map[int]actionType
+	Execmap      map[int]string
+	PrintQuery   bool
+	ReadZero     bool
+	Sync         bool
+	History      *History
+	Header       []string
+	HeaderLines  int
+	Margin       [4]string
+	Tabstop      int
+	Version      bool
 }
 
 func defaultTheme() *curses.ColorTheme {
@@ -138,42 +139,43 @@ func defaultTheme() *curses.ColorTheme {
 
 func defaultOptions() *Options {
 	return &Options{
-		Fuzzy:       true,
-		Extended:    true,
-		Case:        CaseSmart,
-		Nth:         make([]Range, 0),
-		WithNth:     make([]Range, 0),
-		Delimiter:   Delimiter{},
-		Sort:        1000,
-		Tac:         false,
-		Criteria:    []criterion{byMatchLen, byLength},
-		Multi:       false,
-		Ansi:        false,
-		Mouse:       true,
-		Theme:       defaultTheme(),
-		Black:       false,
-		Reverse:     false,
-		Cycle:       false,
-		Hscroll:     true,
-		InlineInfo:  false,
-		Prompt:      "> ",
-		Query:       "",
-		Select1:     false,
-		Exit0:       false,
-		Filter:      nil,
-		ToggleSort:  false,
-		Expect:      make(map[int]string),
-		Keymap:      defaultKeymap(),
-		Execmap:     make(map[int]string),
-		PrintQuery:  false,
-		ReadZero:    false,
-		Sync:        false,
-		History:     nil,
-		Header:      make([]string, 0),
-		HeaderLines: 0,
-		Margin:      defaultMargin(),
-		Tabstop:     8,
-		Version:     false}
+		Fuzzy:        true,
+		Extended:     true,
+		Case:         CaseSmart,
+		Nth:          make([]Range, 0),
+		WithNth:      make([]Range, 0),
+		Delimiter:    Delimiter{},
+		Sort:         1000,
+		Tac:          false,
+		Criteria:     []criterion{byMatchLen, byLength},
+		Multi:        false,
+		Ansi:         false,
+		Mouse:        true,
+		Theme:        defaultTheme(),
+		Black:        false,
+		Reverse:      false,
+		Cycle:        false,
+		Hscroll:      true,
+		InlineInfo:   false,
+		Prompt:       "> ",
+		Query:        "",
+		Select1:      false,
+		Exit0:        false,
+		Filter:       nil,
+		ToggleSort:   false,
+		ToggleFollow: false,
+		Expect:       make(map[int]string),
+		Keymap:       make(map[int]actionType),
+		Execmap:      make(map[int]string),
+		PrintQuery:   false,
+		ReadZero:     false,
+		Sync:         false,
+		History:      nil,
+		Header:       make([]string, 0),
+		HeaderLines:  0,
+		Margin:       defaultMargin(),
+		Tabstop:      8,
+		Version:      false}
 }
 
 func help(code int) {
@@ -484,7 +486,7 @@ const (
 	escapedComma = 1
 )
 
-func parseKeymap(keymap map[int]actionType, execmap map[int]string, toggleSort bool, str string) (map[int]actionType, map[int]string, bool) {
+func parseKeymap(keymap map[int]actionType, execmap map[int]string, str string) {
 	if executeRegexp == nil {
 		// Backreferences are not supported.
 		// "~!@#$%^&*;/|".each_char.map { |c| Regexp.escape(c) }.map { |c| "#{c}[^#{c}]*#{c}" }.join('|')
@@ -590,9 +592,10 @@ func parseKeymap(keymap map[int]actionType, execmap map[int]string, toggleSort b
 			keymap[key] = actPreviousHistory
 		case "next-history":
 			keymap[key] = actNextHistory
+		case "toggle-follow":
+			keymap[key] = actToggleFollow
 		case "toggle-sort":
 			keymap[key] = actToggleSort
-			toggleSort = true
 		default:
 			if isExecuteAction(actLower) {
 				var offset int
@@ -613,7 +616,6 @@ func parseKeymap(keymap map[int]actionType, execmap map[int]string, toggleSort b
 			}
 		}
 	}
-	return keymap, execmap, toggleSort
 }
 
 func isExecuteAction(str string) bool {
@@ -635,13 +637,12 @@ func isExecuteAction(str string) bool {
 	return false
 }
 
-func checkToggleSort(keymap map[int]actionType, str string) map[int]actionType {
+func parseToggleSort(keymap map[int]actionType, str string) {
 	keys := parseKeyChords(str, "key name required")
 	if len(keys) != 1 {
 		errorExit("multiple keys specified")
 	}
 	keymap[firstKey(keys)] = actToggleSort
-	return keymap
 }
 
 func strLines(str string) []string {
@@ -691,7 +692,6 @@ func parseMargin(margin string) [4]string {
 }
 
 func parseOptions(opts *Options, allArgs []string) {
-	keymap := make(map[int]actionType)
 	var historyMax int
 	if opts.History == nil {
 		historyMax = defaultHistoryMax
@@ -741,8 +741,7 @@ func parseOptions(opts *Options, allArgs []string) {
 		case "--tiebreak":
 			opts.Criteria = parseTiebreak(nextString(allArgs, &i, "sort criterion required"))
 		case "--bind":
-			keymap, opts.Execmap, opts.ToggleSort =
-				parseKeymap(keymap, opts.Execmap, opts.ToggleSort, nextString(allArgs, &i, "bind expression required"))
+			parseKeymap(opts.Keymap, opts.Execmap, nextString(allArgs, &i, "bind expression required"))
 		case "--color":
 			spec := optionalNextString(allArgs, &i)
 			if len(spec) == 0 {
@@ -751,7 +750,7 @@ func parseOptions(opts *Options, allArgs []string) {
 				opts.Theme = parseTheme(opts.Theme, spec)
 			}
 		case "--toggle-sort":
-			keymap = checkToggleSort(keymap, nextString(allArgs, &i, "key name required"))
+			parseToggleSort(opts.Keymap, nextString(allArgs, &i, "key name required"))
 			opts.ToggleSort = true
 		case "-d", "--delimiter":
 			opts.Delimiter = delimiterRegexp(nextString(allArgs, &i, "delimiter required"))
@@ -869,7 +868,7 @@ func parseOptions(opts *Options, allArgs []string) {
 			} else if match, _ := optString(arg, "-s", "--sort="); match {
 				opts.Sort = 1 // Don't care
 			} else if match, value := optString(arg, "--toggle-sort="); match {
-				keymap = checkToggleSort(keymap, value)
+				parseToggleSort(opts.Keymap, value)
 				opts.ToggleSort = true
 			} else if match, value := optString(arg, "--expect="); match {
 				opts.Expect = parseKeyChords(value, "key names required")
@@ -878,8 +877,7 @@ func parseOptions(opts *Options, allArgs []string) {
 			} else if match, value := optString(arg, "--color="); match {
 				opts.Theme = parseTheme(opts.Theme, value)
 			} else if match, value := optString(arg, "--bind="); match {
-				keymap, opts.Execmap, opts.ToggleSort =
-					parseKeymap(keymap, opts.Execmap, opts.ToggleSort, value)
+				parseKeymap(opts.Keymap, opts.Execmap, value)
 			} else if match, value := optString(arg, "--history="); match {
 				setHistory(value)
 			} else if match, value := optString(arg, "--history-size="); match {
@@ -905,21 +903,32 @@ func parseOptions(opts *Options, allArgs []string) {
 	if opts.Tabstop < 1 {
 		errorExit("tab stop must be a positive integer")
 	}
+}
 
-	// Change default actions for CTRL-N / CTRL-P when --history is used
+func postProcessOptions(opts *Options) *Options {
+	// Default actions for CTRL-N / CTRL-P when --history is set
 	if opts.History != nil {
-		if _, prs := keymap[curses.CtrlP]; !prs {
-			keymap[curses.CtrlP] = actPreviousHistory
+		if _, prs := opts.Keymap[curses.CtrlP]; !prs {
+			opts.Keymap[curses.CtrlP] = actPreviousHistory
 		}
-		if _, prs := keymap[curses.CtrlN]; !prs {
-			keymap[curses.CtrlN] = actNextHistory
+		if _, prs := opts.Keymap[curses.CtrlN]; !prs {
+			opts.Keymap[curses.CtrlN] = actNextHistory
 		}
 	}
 
-	// Override default key bindings
-	for key, act := range keymap {
-		opts.Keymap[key] = act
+	// Extend the default key map
+	keymap := defaultKeymap()
+	for key, act := range opts.Keymap {
+		// Check if actToggleSort or actToggleFollow is set
+		switch act {
+		case actToggleSort:
+			opts.ToggleSort = true
+		case actToggleFollow:
+			opts.ToggleFollow = true
+		}
+		keymap[key] = act
 	}
+	opts.Keymap = keymap
 
 	// If we're not using extended search mode, --nth option becomes irrelevant
 	// if it contains the whole range
@@ -927,10 +936,11 @@ func parseOptions(opts *Options, allArgs []string) {
 		for _, r := range opts.Nth {
 			if r.begin == rangeEllipsis && r.end == rangeEllipsis {
 				opts.Nth = make([]Range, 0)
-				return
+				break
 			}
 		}
 	}
+	return opts
 }
 
 // ParseOptions parses command-line options
@@ -939,9 +949,12 @@ func ParseOptions() *Options {
 
 	// Options from Env var
 	words, _ := shellwords.Parse(os.Getenv("FZF_DEFAULT_OPTS"))
-	parseOptions(opts, words)
+	if len(words) > 0 {
+		parseOptions(opts, words)
+	}
 
 	// Options from command-line arguments
 	parseOptions(opts, os.Args[1:])
-	return opts
+
+	return postProcessOptions(opts)
 }
diff --git a/src/options_test.go b/src/options_test.go
index ef86abe..fd7510e 100644
--- a/src/options_test.go
+++ b/src/options_test.go
@@ -96,6 +96,7 @@ func TestIrrelevantNth(t *testing.T) {
 		opts := defaultOptions()
 		words := []string{"--nth", "..", "-x"}
 		parseOptions(opts, words)
+		postProcessOptions(opts)
 		if len(opts.Nth) != 0 {
 			t.Errorf("nth should be empty: %s", opts.Nth)
 		}
@@ -104,6 +105,7 @@ func TestIrrelevantNth(t *testing.T) {
 		{
 			opts := defaultOptions()
 			parseOptions(opts, words)
+			postProcessOptions(opts)
 			if len(opts.Nth) != 0 {
 				t.Errorf("nth should be empty: %s", opts.Nth)
 			}
@@ -112,6 +114,7 @@ func TestIrrelevantNth(t *testing.T) {
 			opts := defaultOptions()
 			words = append(words, "-x")
 			parseOptions(opts, words)
+			postProcessOptions(opts)
 			if len(opts.Nth) != 2 {
 				t.Errorf("nth should not be empty: %s", opts.Nth)
 			}
@@ -231,17 +234,14 @@ func TestBind(t *testing.T) {
 	keymap := defaultKeymap()
 	execmap := make(map[int]string)
 	check(actBeginningOfLine, keymap[curses.CtrlA])
-	keymap, execmap, toggleSort :=
-		parseKeymap(keymap, execmap, false,
-			"ctrl-a:kill-line,ctrl-b:toggle-sort,c:page-up,alt-z:page-down,"+
-				"f1:execute(ls {}),f2:execute/echo {}, {}, {}/,f3:execute[echo '({})'],f4:execute;less {};,"+
-				"alt-a:execute@echo (,),[,],/,:,;,%,{}@,alt-b:execute;echo (,),[,],/,:,@,%,{};"+
-				",,:abort,::accept,X:execute:\nfoobar,Y:execute(baz)")
-	if !toggleSort {
-		t.Errorf("toggleSort not set")
-	}
+	parseKeymap(keymap, execmap,
+		"ctrl-a:kill-line,ctrl-b:toggle-sort,ctrl-c:toggle-follow,c:page-up,alt-z:page-down,"+
+			"f1:execute(ls {}),f2:execute/echo {}, {}, {}/,f3:execute[echo '({})'],f4:execute;less {};,"+
+			"alt-a:execute@echo (,),[,],/,:,;,%,{}@,alt-b:execute;echo (,),[,],/,:,@,%,{};"+
+			",,:abort,::accept,X:execute:\nfoobar,Y:execute(baz)")
 	check(actKillLine, keymap[curses.CtrlA])
 	check(actToggleSort, keymap[curses.CtrlB])
+	check(actToggleFollow, keymap[curses.CtrlC])
 	check(actPageUp, keymap[curses.AltZ+'c'])
 	check(actAbort, keymap[curses.AltZ+','])
 	check(actAccept, keymap[curses.AltZ+':'])
@@ -259,15 +259,11 @@ func TestBind(t *testing.T) {
 	checkString("\nfoobar,Y:execute(baz)", execmap[curses.AltZ+'X'])
 
 	for idx, char := range []rune{'~', '!', '@', '#', '$', '%', '^', '&', '*', '|', ';', '/'} {
-		keymap, execmap, toggleSort =
-			parseKeymap(keymap, execmap, false, fmt.Sprintf("%d:execute%cfoobar%c", idx%10, char, char))
+		parseKeymap(keymap, execmap, fmt.Sprintf("%d:execute%cfoobar%c", idx%10, char, char))
 		checkString("foobar", execmap[curses.AltZ+int([]rune(fmt.Sprintf("%d", idx%10))[0])])
 	}
 
-	keymap, execmap, toggleSort = parseKeymap(keymap, execmap, false, "f1:abort")
-	if toggleSort {
-		t.Errorf("toggleSort set")
-	}
+	parseKeymap(keymap, execmap, "f1:abort")
 	check(actAbort, keymap[curses.F1])
 }
 
@@ -328,3 +324,63 @@ func TestParseNilTheme(t *testing.T) {
 		t.Errorf("color should now be enabled and customized")
 	}
 }
+
+func TestDefaultCtrlNP(t *testing.T) {
+	check := func(words []string, key int, expected actionType) {
+		opts := defaultOptions()
+		parseOptions(opts, words)
+		postProcessOptions(opts)
+		if opts.Keymap[key] != expected {
+			t.Error()
+		}
+	}
+	check([]string{}, curses.CtrlN, actDown)
+	check([]string{}, curses.CtrlP, actUp)
+
+	check([]string{"--bind=ctrl-n:accept"}, curses.CtrlN, actAccept)
+	check([]string{"--bind=ctrl-p:accept"}, curses.CtrlP, actAccept)
+
+	hist := "--history=/tmp/foo"
+	check([]string{hist}, curses.CtrlN, actNextHistory)
+	check([]string{hist}, curses.CtrlP, actPreviousHistory)
+
+	check([]string{hist, "--bind=ctrl-n:accept"}, curses.CtrlN, actAccept)
+	check([]string{hist, "--bind=ctrl-n:accept"}, curses.CtrlP, actPreviousHistory)
+
+	check([]string{hist, "--bind=ctrl-p:accept"}, curses.CtrlN, actNextHistory)
+	check([]string{hist, "--bind=ctrl-p:accept"}, curses.CtrlP, actAccept)
+}
+
+func TestToggle(t *testing.T) {
+	optsFor := func(words ...string) *Options {
+		opts := defaultOptions()
+		parseOptions(opts, words)
+		postProcessOptions(opts)
+		return opts
+	}
+
+	opts := optsFor()
+	if opts.ToggleSort || opts.ToggleFollow {
+		t.Error()
+	}
+
+	opts = optsFor("--bind=a:toggle-sort")
+	if !opts.ToggleSort || opts.ToggleFollow {
+		t.Error()
+	}
+
+	opts = optsFor("--bind=a:toggle-follow")
+	if opts.ToggleSort || !opts.ToggleFollow {
+		t.Error()
+	}
+
+	opts = optsFor("--bind=a:toggle-sort,b:toggle-follow")
+	if !opts.ToggleSort || !opts.ToggleFollow {
+		t.Error()
+	}
+
+	opts = optsFor("--bind=a:toggle-sort,b:toggle-follow", "--bind=a:up,b:down")
+	if opts.ToggleSort || opts.ToggleFollow {
+		t.Error()
+	}
+}
diff --git a/src/terminal.go b/src/terminal.go
index f1ddc48..430bb19 100644
--- a/src/terminal.go
+++ b/src/terminal.go
@@ -21,42 +21,44 @@ import (
 
 // Terminal represents terminal input/output
 type Terminal struct {
-	initDelay  time.Duration
-	inlineInfo bool
-	prompt     string
-	reverse    bool
-	hscroll    bool
-	cx         int
-	cy         int
-	offset     int
-	yanked     []rune
-	input      []rune
-	multi      bool
-	sort       bool
-	toggleSort bool
-	expect     map[int]string
-	keymap     map[int]actionType
-	execmap    map[int]string
-	pressed    string
-	printQuery bool
-	history    *History
-	cycle      bool
-	header     []string
-	header0    []string
-	ansi       bool
-	margin     [4]string
-	marginInt  [4]int
-	count      int
-	progress   int
-	reading    bool
-	merger     *Merger
-	selected   map[int32]selectedItem
-	reqBox     *util.EventBox
-	eventBox   *util.EventBox
-	mutex      sync.Mutex
-	initFunc   func()
-	suppress   bool
-	startChan  chan bool
+	initDelay    time.Duration
+	inlineInfo   bool
+	prompt       string
+	reverse      bool
+	hscroll      bool
+	cx           int
+	cy           int
+	offset       int
+	yanked       []rune
+	input        []rune
+	multi        bool
+	sort         bool
+	follow       bool
+	toggleSort   bool
+	toggleFollow bool
+	expect       map[int]string
+	keymap       map[int]actionType
+	execmap      map[int]string
+	pressed      string
+	printQuery   bool
+	history      *History
+	cycle        bool
+	header       []string
+	header0      []string
+	ansi         bool
+	margin       [4]string
+	marginInt    [4]int
+	count        int
+	progress     int
+	reading      bool
+	merger       *Merger
+	selected     map[int32]selectedItem
+	reqBox       *util.EventBox
+	eventBox     *util.EventBox
+	mutex        sync.Mutex
+	initFunc     func()
+	suppress     bool
+	startChan    chan bool
 }
 
 type selectedItem struct {
@@ -131,6 +133,7 @@ const (
 	actUp
 	actPageUp
 	actPageDown
+	actToggleFollow
 	actToggleSort
 	actPreviousHistory
 	actNextHistory
@@ -205,39 +208,41 @@ func NewTerminal(opts *Options, eventBox *util.EventBox) *Terminal {
 		delay = initialDelay
 	}
 	return &Terminal{
-		initDelay:  delay,
-		inlineInfo: opts.InlineInfo,
-		prompt:     opts.Prompt,
-		reverse:    opts.Reverse,
-		hscroll:    opts.Hscroll,
-		cx:         len(input),
-		cy:         0,
-		offset:     0,
-		yanked:     []rune{},
-		input:      input,
-		multi:      opts.Multi,
-		sort:       opts.Sort > 0,
-		toggleSort: opts.ToggleSort,
-		expect:     opts.Expect,
-		keymap:     opts.Keymap,
-		execmap:    opts.Execmap,
-		pressed:    "",
-		printQuery: opts.PrintQuery,
-		history:    opts.History,
-		margin:     opts.Margin,
-		marginInt:  [4]int{0, 0, 0, 0},
-		cycle:      opts.Cycle,
-		header:     header,
-		header0:    header,
-		ansi:       opts.Ansi,
-		reading:    true,
-		merger:     EmptyMerger,
-		selected:   make(map[int32]selectedItem),
-		reqBox:     util.NewEventBox(),
-		eventBox:   eventBox,
-		mutex:      sync.Mutex{},
-		suppress:   true,
-		startChan:  make(chan bool, 1),
+		initDelay:    delay,
+		inlineInfo:   opts.InlineInfo,
+		prompt:       opts.Prompt,
+		reverse:      opts.Reverse,
+		hscroll:      opts.Hscroll,
+		cx:           len(input),
+		cy:           0,
+		offset:       0,
+		yanked:       []rune{},
+		input:        input,
+		multi:        opts.Multi,
+		sort:         opts.Sort > 0,
+		toggleSort:   opts.ToggleSort,
+		follow:       true,
+		toggleFollow: opts.Tac && opts.ToggleFollow,
+		expect:       opts.Expect,
+		keymap:       opts.Keymap,
+		execmap:      opts.Execmap,
+		pressed:      "",
+		printQuery:   opts.PrintQuery,
+		history:      opts.History,
+		margin:       opts.Margin,
+		marginInt:    [4]int{0, 0, 0, 0},
+		cycle:        opts.Cycle,
+		header:       header,
+		header0:      header,
+		ansi:         opts.Ansi,
+		reading:      true,
+		merger:       EmptyMerger,
+		selected:     make(map[int32]selectedItem),
+		reqBox:       util.NewEventBox(),
+		eventBox:     eventBox,
+		mutex:        sync.Mutex{},
+		suppress:     true,
+		startChan:    make(chan bool, 1),
 		initFunc: func() {
 			C.Init(opts.Theme, opts.Black, opts.Mouse)
 		}}
@@ -296,6 +301,11 @@ func (t *Terminal) UpdateProgress(progress float32) {
 func (t *Terminal) UpdateList(merger *Merger) {
 	t.mutex.Lock()
 	t.progress = 100
+	if t.toggleFollow && !t.follow {
+		diff := merger.Length() - t.merger.Length()
+		t.cy += diff
+		t.offset += diff
+	}
 	t.merger = merger
 	t.mutex.Unlock()
 	t.reqBox.Set(reqInfo, nil)
@@ -435,12 +445,11 @@ func (t *Terminal) printInfo() {
 	}
 
 	output := fmt.Sprintf("%d/%d", t.merger.Length(), t.count)
-	if t.toggleSort {
-		if t.sort {
-			output += "/S"
-		} else {
-			output += "  "
-		}
+	if t.toggleSort && t.sort {
+		output += "/S"
+	}
+	if t.toggleFollow && t.reading && t.follow {
+		output += "/F"
 	}
 	if t.multi && len(t.selected) > 0 {
 		output += fmt.Sprintf(" (%d)", len(t.selected))
@@ -892,6 +901,8 @@ func (t *Terminal) Loop() {
 			case actInvalid:
 				t.mutex.Unlock()
 				return false
+			case actToggleFollow:
+				t.follow = !t.follow
 			case actToggleSort:
 				t.sort = !t.sort
 				t.eventBox.Set(EvtSearchNew, t.sort)
@@ -1117,25 +1128,8 @@ func (t *Terminal) Loop() {
 }
 
 func (t *Terminal) constrain() {
-	count := t.merger.Length()
-	height := t.maxItems()
-	diffpos := t.cy - t.offset
-
-	t.cy = util.Constrain(t.cy, 0, count-1)
-
-	if t.cy > t.offset+(height-1) {
-		// Ceil
-		t.offset = t.cy - (height - 1)
-	} else if t.offset > t.cy {
-		// Floor
-		t.offset = t.cy
-	}
-
-	// Adjustment
-	if count-t.offset < height {
-		t.offset = util.Max(0, count-height)
-		t.cy = util.Constrain(t.offset+diffpos, 0, count-1)
-	}
+	t.cy = util.Constrain(t.cy, 0, t.merger.Length()-1)
+	t.offset = util.Constrain(t.offset, t.cy-t.maxItems()+1, t.cy)
 	t.offset = util.Max(0, t.offset)
 }
 
diff --git a/test/test_go.rb b/test/test_go.rb
index 7a2d003..48e2970 100644
--- a/test/test_go.rb
+++ b/test/test_go.rb
@@ -450,7 +450,7 @@ class TestGoFZF < TestBase
       tmux.send_keys "seq 1 111 | #{fzf "-m +s --tac #{opt} -q11"}", :Enter
       tmux.until { |lines| lines[-3].include? '> 111' }
       tmux.send_keys :Tab
-      tmux.until { |lines| lines[-2].include? '4/111   (1)' }
+      tmux.until { |lines| lines[-2].include? '4/111 (1)' }
       tmux.send_keys 'C-R'
       tmux.until { |lines| lines[-3].include? '> 11' }
       tmux.send_keys :Tab
@@ -1137,6 +1137,19 @@ class TestGoFZF < TestBase
       `seq 10 | #{FZF} -f '1 | !1'`.lines.map(&:chomp)
   end
 
+  def test_toggle_follow
+    tmux.send_keys "(seq 1000; sleep 0.5; seq 1001 2000; sleep 0.5; seq 2001 3000) | #{fzf '--bind space:toggle-follow --tac'}", :Enter
+    tmux.until { |lines| lines[-2].end_with? '1000/1000/F' }
+    tmux.send_keys :Space
+    tmux.until { |lines| lines[-2].end_with? '1000/1000' }
+    tmux.until { |lines| lines[-2].end_with? '2000/2000' }
+    tmux.send_keys :Space
+    tmux.until { |lines| lines[-2].end_with? '2000/2000/F' }
+    tmux.until { |lines| lines[-2].end_with? '3000/3000' }
+    tmux.send_keys :Down, :Enter
+    assert_equal '2001', readonce.chomp
+  end
+
 private
   def writelines path, lines
     File.unlink path while File.exists? path