Preview filter while browsing an open dropdown; Esc closes only the list

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/ui/form.go

@@ -11,16 +11,39 @@ import (
 //     (and move between the buttons),
 //
 // Enter or Space still opens a dropdown list. While a list is open it gets all keys.
-func arrowNavigation(f *tview.Form) {
+//
+// With hooks, the highlighted entry of an open list is reported while the user
+// moves through it, before anything is selected.
+//
+// cancel is called on Esc, except when Esc only closes an open dropdown list
+// (tview would otherwise treat that as cancelling the whole form).
+func arrowNavigation(f *tview.Form, cancel func(), hooks *browseHooks) {
+	var b browser
+	var closingList bool
+	f.SetCancelFunc(func() {
+		if closingList {
+			closingList = false
+			return
+		}
+		if cancel != nil {
+			cancel()
+		}
+	})
 	f.SetInputCapture(func(ev *tcell.EventKey) *tcell.EventKey {
+		closingList = false
 		item, button := f.GetFocusedItemIndex()
 		if item < 0 && button < 0 {
 			return ev
 		}
 		dd, _ := focusedDropDown(f, item)
 		if dd != nil && dd.IsOpen() {
+			closingList = ev.Key() == tcell.KeyEscape
+			if hooks != nil {
+				b.track(dd, ev, hooks)
+			}
 			return ev
 		}
+		b.dd = nil
 		total := f.GetFormItemCount() + f.GetButtonCount()
 		pos := item
 		if button >= 0 {
@@ -90,3 +113,50 @@ func bindSearchNow(box *tview.Checkbox, searchable func() bool, blocked func())
 		box.SetChecked(false)
 	}
 }
+
+// browseHooks lets a form follow the highlight of an open dropdown list.
+type browseHooks struct {
+	browse func(dd *tview.DropDown, index int) // the highlight moved to entry index
+	abort  func()                              // the list was closed without selecting
+}
+
+// browser mirrors the highlight of an open dropdown list, which tview does
+// not expose: it starts at the current option and follows the navigation keys.
+type browser struct {
+	dd    *tview.DropDown
+	idx   int
+	known bool // false after keys that move the highlight in ways we do not track
+}
+
+func (b *browser) track(dd *tview.DropDown, ev *tcell.EventKey, h *browseHooks) {
+	n := dd.GetOptionCount()
+	if b.dd != dd {
+		cur, _ := dd.GetCurrentOption()
+		b.dd, b.idx, b.known = dd, max(cur, 0), true
+	}
+	move := func(to int) {
+		b.idx = to
+		if b.known && h.browse != nil {
+			h.browse(dd, b.idx)
+		}
+	}
+	switch ev.Key() {
+	case tcell.KeyDown:
+		move((b.idx + 1) % n)
+	case tcell.KeyUp:
+		move((b.idx - 1 + n) % n)
+	case tcell.KeyHome:
+		move(0)
+	case tcell.KeyEnd:
+		move(n - 1)
+	case tcell.KeyEscape:
+		b.dd = nil
+		if h.abort != nil {
+			h.abort()
+		}
+	case tcell.KeyEnter:
+		b.dd = nil // the selection is reported by the dropdown itself
+	default:
+		b.known = false // paging, typed prefixes
+	}
+}