fix: gracefully quit panicking Cmd

tea.go

@@ -290,6 +290,10 @@ func (p *Program) handleCommands(cmds chan Cmd) chan struct{} {
 				// possible to cancel them so we'll have to leak the goroutine
 				// until Cmd returns.
 				go func() {
+					// Recover from panics.
+					if !p.startupOptions.has(withoutCatchPanics) {
+						defer p.recoverFromPanic()
+					}
 					msg := cmd() // this can be long.
 					p.Send(msg)
 				}()
@@ -300,9 +304,22 @@ func (p *Program) handleCommands(cmds chan Cmd) chan struct{} {
 	return ch
 }
 
+func (p *Program) recoverFromPanic() {
+	if r := recover(); r != nil {
+		fmt.Printf("Caught panic:\n\n%s\n\nRestoring terminal...\n\n", r)
+		debug.PrintStack()
+		p.errs <- fmt.Errorf("%v", r)
+		return
+	}
+}
+
 // eventLoop is the central message loop. It receives and handles the default
 // Bubble Tea messages, update the model and triggers redraws.
 func (p *Program) eventLoop(model Model, cmds chan Cmd) (Model, error) {
+	// Recover from panics.
+	if !p.startupOptions.has(withoutCatchPanics) {
+		defer p.recoverFromPanic()
+	}
 	for {
 		select {
 		case <-p.ctx.Done():

tea_test.go

@@ -263,3 +263,53 @@ func TestTeaNoRun(t *testing.T) {
 	m := &testModel{}
 	NewProgram(m, WithInput(&in), WithOutput(&buf))
 }
+
+type panicModel struct {
+	panicOnInit, panicOnUpdate, panicOnView bool
+}
+
+func (m panicModel) Init() Cmd {
+	if m.panicOnInit {
+		panic("init panic")
+	}
+	return nil
+}
+
+func (m panicModel) Update(msg Msg) (Model, Cmd) {
+	return m, func() Msg {
+		if m.panicOnUpdate {
+			panic("update panic")
+		}
+		return Quit
+	}
+}
+func (m panicModel) View() string {
+	if m.panicOnView {
+		panic("view panic")
+	}
+	return ""
+}
+
+func TestPanicRecovery(t *testing.T) {
+	t.Run("recover from panics from model.Update()", func(t *testing.T) {
+		var buf bytes.Buffer
+		var in bytes.Buffer
+		in.Write([]byte("q"))
+
+		NewProgram(panicModel{panicOnUpdate: true}, WithInput(&in), WithOutput(&buf)).Run()
+	})
+	t.Run("recover from panics from model.View()", func(t *testing.T) {
+		var buf bytes.Buffer
+		var in bytes.Buffer
+		in.Write([]byte("q"))
+
+		NewProgram(panicModel{panicOnView: true}, WithInput(&in), WithOutput(&buf)).Run()
+	})
+	t.Run("recover from panics from model.View()", func(t *testing.T) {
+		var buf bytes.Buffer
+		var in bytes.Buffer
+		in.Write([]byte("q"))
+
+		NewProgram(panicModel{panicOnView: true}, WithInput(&in), WithOutput(&buf)).Run()
+	})
+}