Fix --accept-nth being ignored in filter mode (#4636)

The --accept-nth option was not being respected when using --filter mode.
This caused fzf to output entire lines instead of only the specified fields.

Added buildItemTransformer() helper function to consistently apply field
transformations across filter mode (both streaming and non-streaming) and
select1/exit0 modes.

Fixes #4615

src/core.go

@@ -38,6 +38,18 @@ func (r revision) compatible(other revision) bool {
 	return r.major == other.major
 }
 
+func buildItemTransformer(opts *Options) func(*Item) string {
+	if opts.AcceptNth != nil {
+		fn := opts.AcceptNth(opts.Delimiter)
+		return func(item *Item) string {
+			return item.acceptNth(opts.Ansi, opts.Delimiter, fn)
+		}
+	}
+	return func(item *Item) string {
+		return item.AsString(opts.Ansi)
+	}
+}
+
 // Run starts fzf
 func Run(opts *Options) (int, error) {
 	if opts.Filter == nil {
@@ -243,6 +255,8 @@ func Run(opts *Options) (int, error) {
 		pattern := patternBuilder([]rune(*opts.Filter))
 		matcher.sort = pattern.sortable
 
+		transformer := buildItemTransformer(opts)
+
 		found := false
 		if streamingFilter {
 			slab := util.MakeSlab(slab16Size, slab32Size)
@@ -253,7 +267,7 @@ func Run(opts *Options) (int, error) {
 					if chunkList.trans(&item, runes) {
 						mutex.Lock()
 						if result, _, _ := pattern.MatchItem(&item, false, slab); result != nil {
-							opts.Printer(item.text.ToString())
+							opts.Printer(transformer(&item))
 							found = true
 						}
 						mutex.Unlock()
@@ -271,7 +285,7 @@ func Run(opts *Options) (int, error) {
 				chunks:  snapshot,
 				pattern: pattern})
 			for i := 0; i < result.merger.Length(); i++ {
-				opts.Printer(result.merger.Get(i).item.AsString(opts.Ansi))
+				opts.Printer(transformer(result.merger.Get(i).item))
 				found = true
 			}
 		}
@@ -493,15 +507,7 @@ func Run(opts *Options) (int, error) {
 									if len(opts.Expect) > 0 {
 										opts.Printer("")
 									}
-									transformer := func(item *Item) string {
-										return item.AsString(opts.Ansi)
-									}
-									if opts.AcceptNth != nil {
-										fn := opts.AcceptNth(opts.Delimiter)
-										transformer = func(item *Item) string {
-											return item.acceptNth(opts.Ansi, opts.Delimiter, fn)
-										}
-									}
+									transformer := buildItemTransformer(opts)
 									for i := range count {
 										opts.Printer(transformer(merger.Get(i).item))
 									}