Simplify nth comparison when reusing transformed tokens

* Proper clean-up of caches
* Force rerender list after the action

src/core.go

@@ -192,11 +192,12 @@ func Run(opts *Options) (int, error) {
 	}
 
 	nth := opts.Nth
+	nthRevision := 0
 	patternCache := make(map[string]*Pattern)
 	patternBuilder := func(runes []rune) *Pattern {
 		return BuildPattern(cache, patternCache,
 			opts.Fuzzy, opts.FuzzyAlgo, opts.Extended, opts.Case, opts.Normalize, forward, withPos,
-			opts.Filter == nil, nth, opts.Delimiter, runes)
+			opts.Filter == nil, nth, opts.Delimiter, nthRevision, runes)
 	}
 	inputRevision := revision{}
 	snapshotRevision := revision{}
@@ -378,8 +379,10 @@ func Run(opts *Options) (int, error) {
 						if val.nth != nil {
 							// Change nth and clear caches
 							nth = *val.nth
+							nthRevision++
 							patternCache = make(map[string]*Pattern)
-							inputRevision.bumpMajor()
+							cache.Clear()
+							inputRevision.bumpMinor()
 						}
 						if command != nil {
 							useSnapshot = val.sync

src/item.go

@@ -6,10 +6,17 @@ import (
 	"github.com/junegunn/fzf/src/util"
 )
 
+type transformed struct {
+	// Because nth can be changed dynamically by change-nth action, we need to
+	// keep the revision number at the time of transformation.
+	revision int
+	tokens   []Token
+}
+
 // Item represents each input line. 56 bytes.
 type Item struct {
 	text        util.Chars    // 32 = 24 + 1 + 1 + 2 + 4
-	transformed *[]Token      // 8
+	transformed *transformed  // 8
 	origText    *[]byte       // 8
 	colors      *[]ansiOffset // 8
 }

src/pattern.go

@@ -60,6 +60,7 @@ type Pattern struct {
 	cacheKey      string
 	delimiter     Delimiter
 	nth           []Range
+	revision      int
 	procFun       map[termType]algo.Algo
 	cache         *ChunkCache
 }
@@ -72,7 +73,7 @@ func init() {
 
 // BuildPattern builds Pattern object from the given arguments
 func BuildPattern(cache *ChunkCache, patternCache map[string]*Pattern, fuzzy bool, fuzzyAlgo algo.Algo, extended bool, caseMode Case, normalize bool, forward bool,
-	withPos bool, cacheable bool, nth []Range, delimiter Delimiter, runes []rune) *Pattern {
+	withPos bool, cacheable bool, nth []Range, delimiter Delimiter, revision int, runes []rune) *Pattern {
 
 	var asString string
 	if extended {
@@ -140,6 +141,7 @@ func BuildPattern(cache *ChunkCache, patternCache map[string]*Pattern, fuzzy boo
 		sortable:      sortable,
 		cacheable:     cacheable,
 		nth:           nth,
+		revision:      revision,
 		delimiter:     delimiter,
 		cache:         cache,
 		procFun:       make(map[termType]algo.Algo)}
@@ -393,12 +395,15 @@ func (p *Pattern) extendedMatch(item *Item, withPos bool, slab *util.Slab) ([]Of
 
 func (p *Pattern) transformInput(item *Item) []Token {
 	if item.transformed != nil {
-		return *item.transformed
+		transformed := *item.transformed
+		if transformed.revision == p.revision {
+			return transformed.tokens
+		}
 	}
 
 	tokens := Tokenize(item.text.ToString(), p.delimiter)
 	ret := Transform(tokens, p.nth)
-	item.transformed = &ret
+	item.transformed = &transformed{p.revision, ret}
 	return ret
 }
 

src/pattern_test.go

@@ -68,7 +68,7 @@ func buildPattern(fuzzy bool, fuzzyAlgo algo.Algo, extended bool, caseMode Case,
 	withPos bool, cacheable bool, nth []Range, delimiter Delimiter, runes []rune) *Pattern {
 	return BuildPattern(NewChunkCache(), make(map[string]*Pattern),
 		fuzzy, fuzzyAlgo, extended, caseMode, normalize, forward,
-		withPos, cacheable, nth, delimiter, runes)
+		withPos, cacheable, nth, delimiter, 0, runes)
 }
 
 func TestExact(t *testing.T) {
@@ -135,12 +135,12 @@ func TestOrigTextAndTransformed(t *testing.T) {
 		chunk.items[0] = Item{
 			text:        util.ToChars([]byte("junegunn")),
 			origText:    &origBytes,
-			transformed: &trans}
+			transformed: &transformed{pattern.revision, trans}}
 		pattern.extended = extended
 		matches := pattern.matchChunk(&chunk, nil, slab) // No cache
 		if !(matches[0].item.text.ToString() == "junegunn" &&
 			string(*matches[0].item.origText) == "junegunn.choi" &&
-			reflect.DeepEqual(*matches[0].item.transformed, trans)) {
+			reflect.DeepEqual((*matches[0].item.transformed).tokens, trans)) {
 			t.Error("Invalid match result", matches)
 		}
 
@@ -148,7 +148,7 @@ func TestOrigTextAndTransformed(t *testing.T) {
 		if !(match.item.text.ToString() == "junegunn" &&
 			string(*match.item.origText) == "junegunn.choi" &&
 			offsets[0][0] == 0 && offsets[0][1] == 5 &&
-			reflect.DeepEqual(*match.item.transformed, trans)) {
+			reflect.DeepEqual((*match.item.transformed).tokens, trans)) {
 			t.Error("Invalid match result", match, offsets, extended)
 		}
 		if !((*pos)[0] == 4 && (*pos)[1] == 0) {

src/terminal.go

@@ -1626,6 +1626,10 @@ func (t *Terminal) adjustMarginAndPadding() (int, int, [4]int, [4]int) {
 	return screenWidth, screenHeight, marginInt, paddingInt
 }
 
+func (t *Terminal) forceRerenderList() {
+	t.prevLines = make([]itemLine, len(t.prevLines))
+}
+
 func (t *Terminal) resizeWindows(forcePreview bool, redrawBorder bool) {
 	t.forcePreview = forcePreview
 	screenWidth, screenHeight, marginInt, paddingInt := t.adjustMarginAndPadding()
@@ -4639,6 +4643,7 @@ func (t *Terminal) Loop() error {
 				if len(tokens) > 1 {
 					a.a = strings.Join(append(tokens[1:], tokens[0]), "|")
 				}
+				t.forceRerenderList()
 			case actChangeQuery:
 				t.input = []rune(a.a)
 				t.cx = len(t.input)
@@ -5101,7 +5106,7 @@ func (t *Terminal) Loop() error {
 				req(reqList)
 			case actToggleHscroll:
 				// Force re-rendering of the list
-				t.prevLines = make([]itemLine, len(t.prevLines))
+				t.forceRerenderList()
 				t.hscroll = !t.hscroll
 				req(reqList)
 			case actTrackCurrent:

test/test_go.rb

@@ -3721,10 +3721,12 @@ class TestGoFZF < TestBase
 
   def test_change_nth
     input = [
+      *[''] * 1000,
       'foo bar bar bar bar',
       'foo foo bar bar bar',
       'foo foo foo bar bar',
-      'foo foo foo foo bar'
+      'foo foo foo foo bar',
+      *[''] * 1000
     ]
     writelines(input)
     tmux.send_keys %(#{FZF} -qfoo -n1 --bind 'space:change-nth:2|3|4|5|' < #{tempname}), :Enter