Proof of concept: add support for opt-in inside-out keyboard event propagation

application.go

@@ -401,7 +401,7 @@ EventLoop:
 				// Pass other key events to the root primitive.
 				if root != nil && root.HasFocus() {
 					if handler := root.InputHandler(); handler != nil {
-						handler(event, func(p Primitive) {
+						_ = handler(event, func(p Primitive) {
 							a.SetFocus(p)
 						})
 						draw = true

box.go

@@ -59,6 +59,14 @@ type Box struct {
 	// nothing should be forwarded).
 	inputCapture func(event *tcell.EventKey) *tcell.EventKey
 
+	// An optional capture function which receives a key event and returns a bool
+	// which indicates if the event should be potentially further processed by
+	// parents' own inputCaptureAfter function. This can be used to construct
+	// an inside-out event handling chain.
+	// It has a default value of capturing all events, to preserve semantics
+	// of tview (originally, tview never passed events back to parents).
+	inputCaptureAfter func(event *tcell.EventKey) *tcell.EventKey
+
 	// An optional function which is called before the box is drawn.
 	draw func(screen tcell.Screen, x, y, width, height int) (int, int, int, int)
 
@@ -71,13 +79,14 @@ type Box struct {
 // NewBox returns a Box without a border.
 func NewBox() *Box {
 	b := &Box{
-		width:           15,
-		height:          10,
-		innerX:          -1, // Mark as uninitialized.
-		backgroundColor: Styles.PrimitiveBackgroundColor,
-		borderStyle:     tcell.StyleDefault.Foreground(Styles.BorderColor).Background(Styles.PrimitiveBackgroundColor),
-		titleColor:      Styles.TitleColor,
-		titleAlign:      AlignCenter,
+		width:             15,
+		height:            10,
+		innerX:            -1, // Mark as uninitialized.
+		backgroundColor:   Styles.PrimitiveBackgroundColor,
+		borderStyle:       tcell.StyleDefault.Foreground(Styles.BorderColor).Background(Styles.PrimitiveBackgroundColor),
+		titleColor:        Styles.TitleColor,
+		titleAlign:        AlignCenter,
+		inputCaptureAfter: func(event *tcell.EventKey) *tcell.EventKey { return nil },
 	}
 	return b
 }
@@ -158,19 +167,29 @@ func (b *Box) GetDrawFunc() func(screen tcell.Screen, x, y, width, height int) (
 // on to the provided (default) input handler.
 //
 // This is only meant to be used by subclassing primitives.
-func (b *Box) WrapInputHandler(inputHandler func(*tcell.EventKey, func(p Primitive))) func(*tcell.EventKey, func(p Primitive)) {
-	return func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (b *Box) WrapInputHandler(inputHandler func(*tcell.EventKey, func(p Primitive)) (consumed bool)) func(*tcell.EventKey, func(p Primitive)) (consumed bool) {
+	return func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		if b.inputCapture != nil {
 			event = b.inputCapture(event)
+			if event == nil {
+				consumed = true
+			}
 		}
-		if event != nil && inputHandler != nil {
-			inputHandler(event, setFocus)
+		if event != nil && !consumed && inputHandler != nil {
+			consumed = inputHandler(event, setFocus)
 		}
+		if event != nil && !consumed && b.inputCaptureAfter != nil {
+			event = b.inputCaptureAfter(event)
+			if event == nil {
+				consumed = true
+			}
+		}
+		return
 	}
 }
 
 // InputHandler returns nil. Box has no default input handling.
-func (b *Box) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (b *Box) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 	return b.WrapInputHandler(nil)
 }
 
@@ -206,12 +225,39 @@ func (b *Box) SetInputCapture(capture func(event *tcell.EventKey) *tcell.EventKe
 	return b
 }
 
+// SetInputCaptureAfter installs a function which captures key events after they are
+// forwarded to the primitive's default key event handler. This function can
+// then choose to consume the event and prevent any further processing by
+// returning nil. If a non-nil event is returned, it will be passed back to
+// parent, and potentially further up the tree.
+//
+// Providing a nil handler will remove a previously existing handler. NOTE:
+// the default value of this function is a function which captures all
+// events, so setting it to nil, will instead configure to capture none.
+//
+// This function can also be used on container primitives (like Flex, Grid, or
+// Form) as keyboard events will likewise just be given back to the parent,
+// and processed if it has its own InputCaptureAfter.
+//
+// Pasted key events are not forwarded to the input capture function if pasting
+// is enabled (see [Application.EnablePaste]).
+func (b *Box) SetInputCaptureAfter(capture func(event *tcell.EventKey) *tcell.EventKey) *Box {
+	b.inputCaptureAfter = capture
+	return b
+}
+
 // GetInputCapture returns the function installed with SetInputCapture() or nil
 // if no such function has been installed.
 func (b *Box) GetInputCapture() func(event *tcell.EventKey) *tcell.EventKey {
 	return b.inputCapture
 }
 
+// GetInputCaptureAfter returns the function installed with SetInputCaptureAfter() or nil
+// if no such function has been installed.
+func (b *Box) GetInputCaptureAfter() func(event *tcell.EventKey) *tcell.EventKey {
+	return b.inputCaptureAfter
+}
+
 // WrapMouseHandler wraps a mouse event handler (see [Box.MouseHandler]) with the
 // functionality to capture mouse events (see [Box.SetMouseCapture]) before passing
 // them on to the provided (default) event handler.

button.go

@@ -160,8 +160,8 @@ func (b *Button) Draw(screen tcell.Screen) {
 }
 
 // InputHandler returns the handler for this primitive.
-func (b *Button) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
-	return b.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (b *Button) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
+	return b.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		if b.disabled {
 			return
 		}
@@ -177,6 +177,8 @@ func (b *Button) InputHandler() func(event *tcell.EventKey, setFocus func(p Prim
 				b.exit(key)
 			}
 		}
+
+		return
 	})
 }
 

checkbox.go

@@ -279,8 +279,8 @@ func (c *Checkbox) Draw(screen tcell.Screen) {
 }
 
 // InputHandler returns the handler for this primitive.
-func (c *Checkbox) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
-	return c.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (c *Checkbox) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
+	return c.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		if c.disabled {
 			return
 		}
@@ -303,6 +303,8 @@ func (c *Checkbox) InputHandler() func(event *tcell.EventKey, setFocus func(p Pr
 				c.finished(key)
 			}
 		}
+
+		return
 	})
 }
 

demos/primitive/main.go

@@ -42,8 +42,8 @@ func (r *RadioButtons) Draw(screen tcell.Screen) {
 }
 
 // InputHandler returns the handler for this primitive.
-func (r *RadioButtons) InputHandler() func(event *tcell.EventKey, setFocus func(p tview.Primitive)) {
-	return r.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p tview.Primitive)) {
+func (r *RadioButtons) InputHandler() func(event *tcell.EventKey, setFocus func(p tview.Primitive)) (consumed bool) {
+	return r.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p tview.Primitive)) (consumed bool) {
 		switch event.Key() {
 		case tcell.KeyUp:
 			r.currentOption--
@@ -56,6 +56,8 @@ func (r *RadioButtons) InputHandler() func(event *tcell.EventKey, setFocus func(
 				r.currentOption = len(r.options) - 1
 			}
 		}
+
+		return
 	})
 }
 

dropdown.go

@@ -448,8 +448,8 @@ func (d *DropDown) Draw(screen tcell.Screen) {
 }
 
 // InputHandler returns the handler for this primitive.
-func (d *DropDown) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
-	return d.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (d *DropDown) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
+	return d.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		if d.disabled {
 			return
 		}
@@ -482,6 +482,8 @@ func (d *DropDown) InputHandler() func(event *tcell.EventKey, setFocus func(p Pr
 				d.finished(key)
 			}
 		}
+
+		return
 	})
 }
 

flex.go

@@ -247,16 +247,17 @@ func (f *Flex) MouseHandler() func(action MouseAction, event *tcell.EventMouse,
 }
 
 // InputHandler returns the handler for this primitive.
-func (f *Flex) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
-	return f.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (f *Flex) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
+	return f.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		for _, item := range f.items {
 			if item.Item != nil && item.Item.HasFocus() {
 				if handler := item.Item.InputHandler(); handler != nil {
-					handler(event, setFocus)
+					consumed = handler(event, setFocus)
 					return
 				}
 			}
 		}
+		return
 	})
 }
 

form.go

@@ -846,12 +846,12 @@ func (f *Form) MouseHandler() func(action MouseAction, event *tcell.EventMouse,
 }
 
 // InputHandler returns the handler for this primitive.
-func (f *Form) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
-	return f.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (f *Form) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
+	return f.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		for _, item := range f.items {
 			if item != nil && item.HasFocus() {
 				if handler := item.InputHandler(); handler != nil {
-					handler(event, setFocus)
+					consumed = handler(event, setFocus)
 					return
 				}
 			}
@@ -860,11 +860,13 @@ func (f *Form) InputHandler() func(event *tcell.EventKey, setFocus func(p Primit
 		for _, button := range f.buttons {
 			if button.HasFocus() {
 				if handler := button.InputHandler(); handler != nil {
-					handler(event, setFocus)
+					consumed = handler(event, setFocus)
 					return
 				}
 			}
 		}
+
+		return
 	})
 }
 

frame.go

@@ -209,15 +209,16 @@ func (f *Frame) MouseHandler() func(action MouseAction, event *tcell.EventMouse,
 }
 
 // InputHandler returns the handler for this primitive.
-func (f *Frame) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
-	return f.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (f *Frame) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
+	return f.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		if f.primitive == nil {
 			return
 		}
 		if handler := f.primitive.InputHandler(); handler != nil {
-			handler(event, setFocus)
+			consumed = handler(event, setFocus)
 			return
 		}
+		return
 	})
 }
 

grid.go

@@ -653,14 +653,14 @@ func (g *Grid) MouseHandler() func(action MouseAction, event *tcell.EventMouse,
 }
 
 // InputHandler returns the handler for this primitive.
-func (g *Grid) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
-	return g.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (g *Grid) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
+	return g.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		if !g.hasFocus {
 			// Pass event on to child primitive.
 			for _, item := range g.items {
 				if item != nil && item.Item.HasFocus() {
 					if handler := item.Item.InputHandler(); handler != nil {
-						handler(event, setFocus)
+						consumed = handler(event, setFocus)
 						return
 					}
 				}
@@ -698,6 +698,8 @@ func (g *Grid) InputHandler() func(event *tcell.EventKey, setFocus func(p Primit
 		case tcell.KeyRight:
 			g.columnOffset++
 		}
+
+		return
 	})
 }
 

inputfield.go

@@ -508,8 +508,8 @@ func (i *InputField) Draw(screen tcell.Screen) {
 }
 
 // InputHandler returns the handler for this primitive.
-func (i *InputField) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
-	return i.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (i *InputField) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
+	return i.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		if i.textArea.GetDisabled() {
 			return
 		}
@@ -610,8 +610,10 @@ func (i *InputField) InputHandler() func(event *tcell.EventKey, setFocus func(p
 			fallthrough
 		default:
 			// Forward other key events to the text area.
-			i.textArea.InputHandler()(event, setFocus)
+			consumed = i.textArea.InputHandler()(event, setFocus)
 		}
+
+		return
 	})
 }
 

list.go

@@ -568,8 +568,8 @@ func (l *List) adjustOffset() {
 }
 
 // InputHandler returns the handler for this primitive.
-func (l *List) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
-	return l.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (l *List) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
+	return l.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		if event.Key() == tcell.KeyEscape {
 			if l.done != nil {
 				l.done()
@@ -663,6 +663,8 @@ func (l *List) InputHandler() func(event *tcell.EventKey, setFocus func(p Primit
 			}
 			l.adjustOffset()
 		}
+
+		return
 	})
 }
 

modal.go

@@ -202,13 +202,14 @@ func (m *Modal) MouseHandler() func(action MouseAction, event *tcell.EventMouse,
 }
 
 // InputHandler returns the handler for this primitive.
-func (m *Modal) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
-	return m.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (m *Modal) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
+	return m.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		if m.frame.HasFocus() {
 			if handler := m.frame.InputHandler(); handler != nil {
-				handler(event, setFocus)
+				consumed = handler(event, setFocus)
 				return
 			}
 		}
+		return
 	})
 }

pages.go

@@ -303,16 +303,17 @@ func (p *Pages) MouseHandler() func(action MouseAction, event *tcell.EventMouse,
 }
 
 // InputHandler returns the handler for this primitive.
-func (p *Pages) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) {
-	return p.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) {
+func (p *Pages) InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
+	return p.WrapInputHandler(func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool) {
 		for _, page := range p.pages {
 			if page.Item.HasFocus() {
 				if handler := page.Item.InputHandler(); handler != nil {
-					handler(event, setFocus)
+					consumed = handler(event, setFocus)
 					return
 				}
 			}
 		}
+		return
 	})
 }
 

primitive.go

@@ -32,7 +32,7 @@ type Primitive interface {
 	// The Box class provides functionality to intercept keyboard input. If you
 	// subclass from Box, it is recommended that you wrap your handler using
 	// Box.WrapInputHandler() so you inherit that functionality.
-	InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive))
+	InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive)) (consumed bool)
 
 	// Focus is called by the application when the primitive receives focus.
 	// Implementers may call delegate() to pass the focus on to another primitive.