Allowing container.Option to report an error.

container/container.go

@@ -64,7 +64,7 @@ func (c *Container) String() string {
 
 // New returns a new root container that will use the provided terminal and
 // applies the provided options.
-func New(t terminalapi.Terminal, opts ...Option) *Container {
+func New(t terminalapi.Terminal, opts ...Option) (*Container, error) {
 	size := t.Size()
 	root := &Container{
 		term: t,
@@ -75,8 +75,10 @@ func New(t terminalapi.Terminal, opts ...Option) *Container {
 
 	// Initially the root is focused.
 	root.focusTracker = newFocusTracker(root)
-	applyOptions(root, opts...)
+	if err := applyOptions(root, opts...); err != nil {
-	return root
+		return nil, err
+	}
+	return root, nil
 }
 
 // newChild creates a new child container of the given parent.

container/container_test.go

@@ -33,7 +33,7 @@ import (
 
 // Example demonstrates how to use the Container API.
 func Example() {
-	New(
+	if _, err := New(
 		/* terminal = */ nil,
 		SplitVertical(
 			Left(
@@ -58,20 +58,23 @@ func Example() {
 				PlaceWidget(fakewidget.New(widgetapi.Options{})),
 			),
 		),
-	)
+	); err != nil {
+		panic(err)
+	}
 }
 
 func TestNew(t *testing.T) {
 	tests := []struct {
 		desc             string
 		termSize         image.Point
-		container func(ft *faketerm.Terminal) *Container
+		container        func(ft *faketerm.Terminal) (*Container, error)
+		wantContainerErr bool
 		want             func(size image.Point) *faketerm.Terminal
 	}{
 		{
 			desc:     "empty container",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(ft)
 			},
 			want: func(size image.Point) *faketerm.Terminal {
@@ -81,7 +84,7 @@ func TestNew(t *testing.T) {
 		{
 			desc:     "container with a border",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -102,7 +105,7 @@ func TestNew(t *testing.T) {
 		{
 			desc:     "horizontal split, children have borders",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					SplitHorizontal(
@@ -127,7 +130,7 @@ func TestNew(t *testing.T) {
 		{
 			desc:     "horizontal split, parent and children have borders",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -158,7 +161,7 @@ func TestNew(t *testing.T) {
 		{
 			desc:     "vertical split, children have borders",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					SplitVertical(
@@ -183,7 +186,7 @@ func TestNew(t *testing.T) {
 		{
 			desc:     "vertical split, parent and children have borders",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -214,7 +217,7 @@ func TestNew(t *testing.T) {
 		{
 			desc:     "multi level split",
 			termSize: image.Point{10, 16},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					SplitVertical(
@@ -255,7 +258,7 @@ func TestNew(t *testing.T) {
 		{
 			desc:     "inherits border and focused color",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -296,7 +299,7 @@ func TestNew(t *testing.T) {
 		{
 			desc:     "splitting a container removes the widget",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -328,7 +331,7 @@ func TestNew(t *testing.T) {
 		{
 			desc:     "placing a widget removes container split",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					SplitVertical(
@@ -360,7 +363,14 @@ func TestNew(t *testing.T) {
 				t.Fatalf("faketerm.New => unexpected error: %v", err)
 			}
 
-			if err := tc.container(got).Draw(); err != nil {
+			cont, err := tc.container(got)
+			if (err != nil) != tc.wantContainerErr {
+				t.Errorf("tc.container => unexpected error:%v, wantErr:%v", err, tc.wantContainerErr)
+			}
+			if err != nil {
+				return
+			}
+			if err := cont.Draw(); err != nil {
 				t.Fatalf("Draw => unexpected error: %v", err)
 			}
 
@@ -376,7 +386,7 @@ func TestKeyboard(t *testing.T) {
 	tests := []struct {
 		desc      string
 		termSize  image.Point
-		container func(ft *faketerm.Terminal) *Container
+		container func(ft *faketerm.Terminal) (*Container, error)
 		events    []terminalapi.Event
 		want      func(size image.Point) *faketerm.Terminal
 		wantErr   bool
@@ -384,7 +394,7 @@ func TestKeyboard(t *testing.T) {
 		{
 			desc:     "event not forwarded if container has no widget",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(ft)
 			},
 			events: []terminalapi.Event{
@@ -397,7 +407,7 @@ func TestKeyboard(t *testing.T) {
 		{
 			desc:     "event forwarded to focused container only",
 			termSize: image.Point{40, 20},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					SplitVertical(
@@ -450,7 +460,7 @@ func TestKeyboard(t *testing.T) {
 		{
 			desc:     "event not forwarded if the widget didn't request it",
 			termSize: image.Point{40, 20},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					PlaceWidget(fakewidget.New(widgetapi.Options{WantKeyboard: false})),
@@ -473,7 +483,7 @@ func TestKeyboard(t *testing.T) {
 		{
 			desc:     "widget returns an error when processing the event",
 			termSize: image.Point{40, 20},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					PlaceWidget(fakewidget.New(widgetapi.Options{WantKeyboard: true})),
@@ -503,7 +513,10 @@ func TestKeyboard(t *testing.T) {
 				t.Fatalf("faketerm.New => unexpected error: %v", err)
 			}
 
-			c := tc.container(got)
+			c, err := tc.container(got)
+			if err != nil {
+				t.Fatalf("tc.container => unexpected error: %v", err)
+			}
 			for _, ev := range tc.events {
 				switch e := ev.(type) {
 				case *terminalapi.Mouse:
@@ -537,7 +550,7 @@ func TestMouse(t *testing.T) {
 	tests := []struct {
 		desc      string
 		termSize  image.Point
-		container func(ft *faketerm.Terminal) *Container
+		container func(ft *faketerm.Terminal) (*Container, error)
 		events    []terminalapi.Event
 		want      func(size image.Point) *faketerm.Terminal
 		wantErr   bool
@@ -545,7 +558,7 @@ func TestMouse(t *testing.T) {
 		{
 			desc:     "mouse click outside of the terminal is ignored",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					PlaceWidget(fakewidget.New(widgetapi.Options{WantMouse: true})),
@@ -569,7 +582,7 @@ func TestMouse(t *testing.T) {
 		{
 			desc:     "event not forwarded if container has no widget",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(ft)
 			},
 			events: []terminalapi.Event{
@@ -583,7 +596,7 @@ func TestMouse(t *testing.T) {
 		{
 			desc:     "event forwarded to container at that point",
 			termSize: image.Point{50, 20},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					SplitVertical(
@@ -636,7 +649,7 @@ func TestMouse(t *testing.T) {
 		{
 			desc:     "event not forwarded if the widget didn't request it",
 			termSize: image.Point{20, 20},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					PlaceWidget(fakewidget.New(widgetapi.Options{WantMouse: false})),
@@ -659,7 +672,7 @@ func TestMouse(t *testing.T) {
 		{
 			desc:     "event not forwarded if it falls on the container's border",
 			termSize: image.Point{20, 20},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -693,7 +706,7 @@ func TestMouse(t *testing.T) {
 		{
 			desc:     "event not forwarded if it falls outside of widget's canvas",
 			termSize: image.Point{20, 20},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					PlaceWidget(
@@ -723,7 +736,7 @@ func TestMouse(t *testing.T) {
 		{
 			desc:     "mouse poisition adjusted relative to widget's canvas, vertical offset",
 			termSize: image.Point{20, 20},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					PlaceWidget(
@@ -754,7 +767,7 @@ func TestMouse(t *testing.T) {
 		{
 			desc:     "mouse poisition adjusted relative to widget's canvas, horizontal offset",
 			termSize: image.Point{30, 20},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					PlaceWidget(
@@ -785,7 +798,7 @@ func TestMouse(t *testing.T) {
 		{
 			desc:     "widget returns an error when processing the event",
 			termSize: image.Point{40, 20},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					PlaceWidget(fakewidget.New(widgetapi.Options{WantMouse: true})),
@@ -815,7 +828,10 @@ func TestMouse(t *testing.T) {
 				t.Fatalf("faketerm.New => unexpected error: %v", err)
 			}
 
-			c := tc.container(got)
+			c, err := tc.container(got)
+			if err != nil {
+				t.Fatalf("tc.container => unexpected error: %v", err)
+			}
 			for _, ev := range tc.events {
 				switch e := ev.(type) {
 				case *terminalapi.Mouse:

container/draw_test.go

@@ -32,14 +32,14 @@ func TestDrawWidget(t *testing.T) {
 	tests := []struct {
 		desc      string
 		termSize  image.Point
-		container func(ft *faketerm.Terminal) *Container
+		container func(ft *faketerm.Terminal) (*Container, error)
 		want      func(size image.Point) *faketerm.Terminal
 		wantErr   bool
 	}{
 		{
 			desc:     "draws widget with container border",
 			termSize: image.Point{9, 5},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -66,7 +66,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "draws widget with container border and title aligned on the left",
 			termSize: image.Point{9, 5},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -100,7 +100,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "draws widget with container border and title aligned in the center",
 			termSize: image.Point{9, 5},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -135,7 +135,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "draws widget with container border and title aligned on the right",
 			termSize: image.Point{9, 5},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -170,7 +170,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "draws widget with container border and title that is trimmed",
 			termSize: image.Point{9, 5},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -205,7 +205,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "draws widget without container border",
 			termSize: image.Point{9, 5},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					PlaceWidget(fakewidget.New(widgetapi.Options{})),
@@ -225,7 +225,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "widget.Draw returns an error",
 			termSize: image.Point{5, 5}, // Too small for the widget's box.
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -240,7 +240,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "container with border and no space isn't drawn",
 			termSize: image.Point{1, 1},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -257,7 +257,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "container without the requested space for its widget isn't drawn",
 			termSize: image.Point{1, 1},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					PlaceWidget(fakewidget.New(widgetapi.Options{
@@ -276,7 +276,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "widget's canvas is limited to the requested maximum size",
 			termSize: image.Point{22, 22},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -308,7 +308,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "widget's canvas is limited to the requested maximum width",
 			termSize: image.Point{22, 22},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -340,7 +340,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "widget's canvas is limited to the requested maximum height",
 			termSize: image.Point{22, 22},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -372,7 +372,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "widget gets the requested aspect ratio",
 			termSize: image.Point{22, 22},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -404,7 +404,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "widget's canvas is limited to the requested maximum size and ratio",
 			termSize: image.Point{22, 22},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -436,7 +436,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "horizontal left align for the widget",
 			termSize: image.Point{22, 22},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -467,7 +467,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "horizontal center align for the widget",
 			termSize: image.Point{22, 22},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -498,7 +498,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "horizontal right align for the widget",
 			termSize: image.Point{22, 22},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -529,7 +529,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "vertical top align for the widget",
 			termSize: image.Point{22, 22},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -560,7 +560,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "vertical middle align for the widget",
 			termSize: image.Point{22, 22},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -591,7 +591,7 @@ func TestDrawWidget(t *testing.T) {
 		{
 			desc:     "vertical bottom align for the widget",
 			termSize: image.Point{22, 22},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -624,8 +624,11 @@ func TestDrawWidget(t *testing.T) {
 	for _, tc := range tests {
 		t.Run(tc.desc, func(t *testing.T) {
 			got := faketerm.MustNew(tc.termSize)
-			c := tc.container(got)
+			c, err := tc.container(got)
-			err := c.Draw()
+			if err != nil {
+				t.Fatalf("tc.container => unexpected error: %v", err)
+			}
+			err = c.Draw()
 			if (err != nil) != tc.wantErr {
 				t.Errorf("Draw => unexpected error: %v, wantErr: %v", err, tc.wantErr)
 			}
@@ -647,7 +650,7 @@ func TestDrawHandlesTerminalResize(t *testing.T) {
 		t.Errorf("faketerm.New => unexpected error: %v", err)
 	}
 
-	cont := New(
+	cont, err := New(
 		got,
 		SplitVertical(
 			Left(
@@ -672,6 +675,9 @@ func TestDrawHandlesTerminalResize(t *testing.T) {
 			),
 		),
 	)
+	if err != nil {
+		t.Fatalf("New => unexpected error: %v", err)
+	}
 
 	// The following tests aren't hermetic, they all access the same container
 	// and fake terminal in order to retain state between resizes.

container/focus_test.go

@@ -37,13 +37,13 @@ func TestPointCont(t *testing.T) {
 	tests := []struct {
 		desc      string
 		termSize  image.Point
-		container func(ft *faketerm.Terminal) *Container
+		container func(ft *faketerm.Terminal) (*Container, error)
 		cases     []pointCase
 	}{
 		{
 			desc:     "single container, no border",
 			termSize: image.Point{3, 3},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					BorderColor(cell.ColorBlue),
@@ -90,7 +90,7 @@ func TestPointCont(t *testing.T) {
 		{
 			desc:     "single container, border",
 			termSize: image.Point{3, 3},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -113,7 +113,7 @@ func TestPointCont(t *testing.T) {
 		{
 			desc:     "split containers, parent has no border",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					BorderColor(cell.ColorBlack),
@@ -160,7 +160,7 @@ func TestPointCont(t *testing.T) {
 		{
 			desc:     "split containers, parent has border",
 			termSize: image.Point{10, 10},
-			container: func(ft *faketerm.Terminal) *Container {
+			container: func(ft *faketerm.Terminal) (*Container, error) {
 				return New(
 					ft,
 					Border(draw.LineStyleLight),
@@ -229,7 +229,10 @@ func TestPointCont(t *testing.T) {
 				t.Fatalf("faketerm.New => unexpected error: %v", err)
 			}
 
-			cont := tc.container(ft)
+			cont, err := tc.container(ft)
+			if err != nil {
+				t.Fatalf("tc.container => unexpected error: %v", err)
+			}
 			for _, pc := range tc.cases {
 				gotCont := pointCont(cont, pc.point)
 				if (gotCont == nil) != pc.wantNil {
@@ -382,13 +385,16 @@ func TestFocusTrackerMouse(t *testing.T) {
 
 	for _, tc := range tests {
 		t.Run(tc.desc, func(t *testing.T) {
-			root := New(
+			root, err := New(
 				ft,
 				SplitVertical(
 					Left(),
 					Right(),
 				),
 			)
+			if err != nil {
+				t.Fatalf("New => unexpected error: %v", err)
+			}
 
 			for _, ev := range tc.events {
 				root.Mouse(ev)

container/options.go

@@ -24,16 +24,19 @@ import (
 )
 
 // applyOptions applies the options to the container.
-func applyOptions(c *Container, opts ...Option) {
+func applyOptions(c *Container, opts ...Option) error {
 	for _, opt := range opts {
-		opt.set(c)
+		if err := opt.set(c); err != nil {
+			return err
 		}
 	}
+	return nil
+}
 
 // Option is used to provide options to a container.
 type Option interface {
 	// set sets the provided option.
-	set(*Container)
+	set(*Container) error
 }
 
 // options stores the options provided to the container.
@@ -85,22 +88,24 @@ func newOptions(parent *options) *options {
 }
 
 // option implements Option.
-type option func(*Container)
+type option func(*Container) error
 
 // set implements Option.set.
-func (o option) set(c *Container) {
+func (o option) set(c *Container) error {
-	o(c)
+	return o(c)
 }
 
 // SplitVertical splits the container along the vertical axis into two sub
 // containers. The use of this option removes any widget placed at this
 // container, containers with sub containers cannot contain widgets.
 func SplitVertical(l LeftOption, r RightOption) Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.split = splitTypeVertical
 		c.opts.widget = nil
-		applyOptions(c.createFirst(), l.lOpts()...)
+		if err := applyOptions(c.createFirst(), l.lOpts()...); err != nil {
-		applyOptions(c.createSecond(), r.rOpts()...)
+			return err
+		}
+		return applyOptions(c.createSecond(), r.rOpts()...)
 	})
 }
 
@@ -108,11 +113,13 @@ func SplitVertical(l LeftOption, r RightOption) Option {
 // containers. The use of this option removes any widget placed at this
 // container, containers with sub containers cannot contain widgets.
 func SplitHorizontal(t TopOption, b BottomOption) Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.split = splitTypeHorizontal
 		c.opts.widget = nil
-		applyOptions(c.createFirst(), t.tOpts()...)
+		if err := applyOptions(c.createFirst(), t.tOpts()...); err != nil {
-		applyOptions(c.createSecond(), b.bOpts()...)
+			return err
+		}
+		return applyOptions(c.createSecond(), b.bOpts()...)
 	})
 }
 
@@ -120,10 +127,11 @@ func SplitHorizontal(t TopOption, b BottomOption) Option {
 // The use of this option removes any sub containers. Containers with sub
 // containers cannot have widgets.
 func PlaceWidget(w widgetapi.Widget) Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.widget = w
 		c.first = nil
 		c.second = nil
+		return nil
 	})
 }
 
@@ -131,8 +139,9 @@ func PlaceWidget(w widgetapi.Widget) Option {
 // container. Has no effect if the container contains no widget.
 // Defaults alignment in the center.
 func AlignHorizontal(h align.Horizontal) Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.hAlign = h
+		return nil
 	})
 }
 
@@ -140,51 +149,58 @@ func AlignHorizontal(h align.Horizontal) Option {
 // Has no effect if the container contains no widget.
 // Defaults to alignment in the middle.
 func AlignVertical(v align.Vertical) Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.vAlign = v
+		return nil
 	})
 }
 
 // Border configures the container to have a border of the specified style.
 func Border(ls draw.LineStyle) Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.border = ls
+		return nil
 	})
 }
 
 // BorderTitle sets a text title within the border.
 func BorderTitle(title string) Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.borderTitle = title
+		return nil
 	})
 }
 
 // BorderTitleAlignLeft aligns the border title on the left.
 func BorderTitleAlignLeft() Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.borderTitleHAlign = align.HorizontalLeft
+		return nil
 	})
 }
 
 // BorderTitleAlignCenter aligns the border title in the center.
 func BorderTitleAlignCenter() Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.borderTitleHAlign = align.HorizontalCenter
+		return nil
 	})
 }
 
 // BorderTitleAlignRight aligns the border title on the right.
 func BorderTitleAlignRight() Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.borderTitleHAlign = align.HorizontalRight
+		return nil
 	})
 }
 
 // BorderColor sets the color of the border around the container.
 // This option is inherited to sub containers created by container splits.
 func BorderColor(color cell.Color) Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.inherited.borderColor = color
+		return nil
 	})
 }
 
@@ -192,8 +208,9 @@ func BorderColor(color cell.Color) Option {
 // keyboard focus.
 // This option is inherited to sub containers created by container splits.
 func FocusedColor(color cell.Color) Option {
-	return option(func(c *Container) {
+	return option(func(c *Container) error {
 		c.opts.inherited.focusedColor = color
+		return nil
 	})
 }
 

container/traversal_test.go

@@ -30,7 +30,7 @@ func TestRoot(t *testing.T) {
 	if err != nil {
 		t.Fatalf("faketerm.New => unexpected error: %v", err)
 	}
-	want := New(
+	want, err := New(
 		ft,
 		SplitHorizontal(
 			Top(
@@ -42,6 +42,9 @@ func TestRoot(t *testing.T) {
 			Bottom(),
 		),
 	)
+	if err != nil {
+		t.Fatalf("New => unexpected error: %v", err)
+	}
 
 	if got := rootCont(want); got != want {
 		t.Errorf("rootCont(root) => got %p, want %p", got, want)
@@ -58,7 +61,7 @@ func TestTraversal(t *testing.T) {
 	if err != nil {
 		t.Fatalf("faketerm.New => unexpected error: %v", err)
 	}
-	cont := New(
+	cont, err := New(
 		ft,
 		BorderColor(cell.ColorBlack),
 		SplitVertical(
@@ -86,6 +89,9 @@ func TestTraversal(t *testing.T) {
 			),
 		),
 	)
+	if err != nil {
+		t.Fatalf("New => unexpected error: %v", err)
+	}
 
 	tests := []struct {
 		desc       string

termdash_test.go

@@ -50,7 +50,7 @@ func Example() {
 	}
 
 	// Create the container with two fake widgets.
-	c := container.New(
+	c, err := container.New(
 		t,
 		container.SplitVertical(
 			container.Left(
@@ -61,6 +61,9 @@ func Example() {
 			),
 		),
 	)
+	if err != nil {
+		panic(err)
+	}
 
 	// Termdash runs until the context expires.
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
@@ -86,10 +89,13 @@ func Example_triggered() {
 	}
 
 	// Create the container with a widget.
-	c := container.New(
+	c, err := container.New(
 		t,
 		container.PlaceWidget(fakewidget.New(wOpts)),
 	)
+	if err != nil {
+		panic(err)
+	}
 
 	// Create the controller and disable periodic redraw.
 	ctrl, err := NewController(t, c)
@@ -332,13 +338,16 @@ func TestRun(t *testing.T) {
 				t.Fatalf("faketerm.New => unexpected error: %v", err)
 			}
 
-			cont := container.New(
+			cont, err := container.New(
 				got,
 				container.PlaceWidget(fakewidget.New(widgetapi.Options{
 					WantKeyboard: true,
 					WantMouse:    true,
 				})),
 			)
+			if err != nil {
+				t.Fatalf("container.New => unexpected error: %v", err)
+			}
 
 			ctx, cancel := context.WithTimeout(context.Background(), 5*time.Millisecond)
 			err = Run(ctx, got, cont, tc.opts...)
@@ -511,10 +520,13 @@ func TestController(t *testing.T) {
 				WantKeyboard: true,
 				WantMouse:    true,
 			})
-			cont := container.New(
+			cont, err := container.New(
 				got,
 				container.PlaceWidget(mi),
 			)
+			if err != nil {
+				t.Fatalf("container.New => unexpected error: %v", err)
+			}
 
 			ctrl, err := NewController(got, cont, tc.opts...)
 			if (err != nil) != tc.wantErr {

widgets/barchart/barchartdemo/barchartdemo.go

@@ -93,12 +93,15 @@ func main() {
 	)
 	go playBarChart(ctx, bc, 1*time.Second)
 
-	c := container.New(
+	c, err := container.New(
 		t,
 		container.Border(draw.LineStyleLight),
 		container.BorderTitle("PRESS Q TO QUIT"),
 		container.PlaceWidget(bc),
 	)
+	if err != nil {
+		panic(err)
+	}
 
 	quitter := func(k *terminalapi.Keyboard) {
 		if k.Key == 'q' || k.Key == 'Q' {

widgets/gauge/demo/gaugedemo.go

@@ -115,7 +115,7 @@ func main() {
 	)
 	go playGauge(ctx, withLabel, 3, 500*time.Millisecond, playTypePercent)
 
-	c := container.New(
+	c, err := container.New(
 		t,
 		container.SplitVertical(
 			container.Left(
@@ -147,6 +147,9 @@ func main() {
 			),
 		),
 	)
+	if err != nil {
+		panic(err)
+	}
 
 	quitter := func(k *terminalapi.Keyboard) {
 		if k.Key == 'q' || k.Key == 'Q' {

widgets/linechart/linechartdemo/linechartdemo.go

@@ -88,12 +88,15 @@ func main() {
 		linechart.XLabelCellOpts(cell.FgColor(cell.ColorCyan)),
 	)
 	go playLineChart(ctx, lc, redrawInterval/3)
-	c := container.New(
+	c, err := container.New(
 		t,
 		container.Border(draw.LineStyleLight),
 		container.BorderTitle("PRESS Q TO QUIT"),
 		container.PlaceWidget(lc),
 	)
+	if err != nil {
+		panic(err)
+	}
 
 	quitter := func(k *terminalapi.Keyboard) {
 		if k.Key == 'q' || k.Key == 'Q' {

widgets/sparkline/sparklinedemo/sparklinedemo.go

@@ -75,7 +75,7 @@ func main() {
 	)
 	go playSparkLine(ctx, yellow, 1*time.Second)
 
-	c := container.New(
+	c, err := container.New(
 		t,
 		container.Border(draw.LineStyleLight),
 		container.BorderTitle("PRESS Q TO QUIT"),
@@ -103,6 +103,9 @@ func main() {
 			),
 		),
 	)
+	if err != nil {
+		panic(err)
+	}
 
 	quitter := func(k *terminalapi.Keyboard) {
 		if k.Key == 'q' || k.Key == 'Q' {

widgets/text/demo/textdemo.go

@@ -106,7 +106,7 @@ func main() {
 	}
 	go writeLines(ctx, rolled, 1*time.Second)
 
-	c := container.New(
+	c, err := container.New(
 		t,
 		container.Border(draw.LineStyleLight),
 		container.BorderTitle("PRESS Q TO QUIT"),
@@ -148,6 +148,9 @@ func main() {
 			),
 		),
 	)
+	if err != nil {
+		panic(err)
+	}
 
 	quitter := func(k *terminalapi.Keyboard) {
 		if k.Key == 'q' || k.Key == 'Q' {