(v2) tea.go: deadlock/error return fixes, additional tests (targeted at v2)

options.go

@@ -21,7 +21,7 @@ type ProgramOption func(*Program)
 // cancelled it will exit with an error ErrProgramKilled.
 func WithContext(ctx context.Context) ProgramOption {
 	return func(p *Program) {
-		p.ctx = ctx
+		p.externalCtx = ctx
 	}
 }
 

options_test.go

@@ -2,6 +2,7 @@ package tea
 
 import (
 	"bytes"
+	"context"
 	"os"
 	"sync/atomic"
 	"testing"
@@ -41,6 +42,16 @@ func TestOptions(t *testing.T) {
 		}
 	})
 
+	t.Run("external context", func(t *testing.T) {
+		extCtx, extCancel := context.WithCancel(context.Background())
+		defer extCancel()
+
+		p := NewProgram(nil, WithContext(extCtx))
+		if p.externalCtx != extCtx || p.externalCtx == context.Background() {
+			t.Errorf("expected passed in external context, got default")
+		}
+	})
+
 	t.Run("input options", func(t *testing.T) {
 		exercise := func(t *testing.T, opt ProgramOption, expect inputType) {
 			p := NewProgram(nil, opt)

tea.go

@@ -32,6 +32,9 @@
 	"golang.org/x/sync/errgroup"
 )
 
+// ErrProgramPanic is returned by [Program.Run] when the program recovers from a panic.
+var ErrProgramPanic = errors.New("program experienced a panic")
+
 // ErrProgramKilled is returned by [Program.Run] when the program gets killed.
 var ErrProgramKilled = errors.New("program was killed")
 
@@ -210,6 +213,12 @@
 
 	inputType inputType
 
+	// externalCtx is a context that was passed in via WithContext, otherwise defaulting
+	// to ctx.Background() (in case it was not), the internal context is derived from it.
+	externalCtx context.Context
+
+	// ctx is the programs's internal context for signalling internal teardown.
+	// It is built and derived from the externalCtx in NewProgram().
 	ctx    context.Context
 	cancel context.CancelFunc
 
@@ -341,11 +350,11 @@
 
 	// A context can be provided with a ProgramOption, but if none was provided
 	// we'll use the default background context.
-	if p.ctx == nil {
-		p.ctx = context.Background()
+	if p.externalCtx == nil {
+		p.externalCtx = context.Background()
 	}
 	// Initialize context and teardown channel.
-	p.ctx, p.cancel = context.WithCancel(p.ctx)
+	p.ctx, p.cancel = context.WithCancel(p.externalCtx)
 
 	// if no output was set, set it to stdout
 	if p.output == nil {
@@ -470,7 +479,11 @@
 				go func() {
 					// Recover from panics.
 					if !p.startupOptions.has(withoutCatchPanics) {
-						defer p.recoverFromPanic()
+						defer func() {
+							if r := recover(); r != nil {
+								p.recoverFromPanic(r)
+							}
+						}()
 					}
 
 					msg := cmd() // this can be long.
@@ -686,7 +699,11 @@
 
 			case BatchMsg:
 				for _, cmd := range msg {
-					cmds <- cmd
+					select {
+					case <-p.ctx.Done():
+						return model, nil
+					case cmds <- cmd:
+					}
 				}
 				continue
 
@@ -751,7 +768,12 @@
 
 			var cmd Cmd
 			model, cmd = model.Update(msg) // run update
-			cmds <- cmd                    // process command (if any)
+
+			select {
+			case <-p.ctx.Done():
+				return model, nil
+			case cmds <- cmd: // process command (if any)
+			}
 
 			p.render(model) // render view
 		}
@@ -789,11 +811,15 @@
 // Run initializes the program and runs its event loops, blocking until it gets
 // terminated by either [Program.Quit], [Program.Kill], or its signal handler.
 // Returns the final model.
-func (p *Program) Run() (Model, error) {
+func (p *Program) Run() (returnModel Model, returnErr error) {
 	p.handlers = channelHandlers{}
 	cmds := make(chan Cmd)
-	p.errs = make(chan error)
-	p.finished = make(chan struct{}, 1)
+	p.errs = make(chan error, 1)
+
+	p.finished = make(chan struct{})
+	defer func() {
+		close(p.finished)
+	}()
 
 	defer p.cancel()
 
@@ -842,7 +868,12 @@
 
 	// Recover from panics.
 	if !p.startupOptions.has(withoutCatchPanics) {
-		defer p.recoverFromPanic()
+		defer func() {
+			if r := recover(); r != nil {
+				returnErr = fmt.Errorf("%w: %w", ErrProgramKilled, ErrProgramPanic)
+				p.recoverFromPanic(r)
+			}
+		}()
 	}
 
 	// Check if output is a TTY before entering raw mode, hiding the cursor and
@@ -986,11 +1017,27 @@
 
 	// Run event loop, handle updates and draw.
 	model, err := p.eventLoop(model, cmds)
-	killed := p.ctx.Err() != nil || err != nil
-	if killed && err == nil {
-		err = fmt.Errorf("%w: %s", ErrProgramKilled, p.ctx.Err())
+
+	if err == nil && len(p.errs) > 0 {
+		err = <-p.errs // Drain a leftover error in case eventLoop crashed.
 	}
-	if err == nil {
+
+	killed := p.externalCtx.Err() != nil || p.ctx.Err() != nil || err != nil
+	if killed {
+		if err == nil && p.externalCtx.Err() != nil {
+			// Return also as context error the cancellation of an external context.
+			// This is the context the user knows about and should be able to act on.
+			err = fmt.Errorf("%w: %w", ErrProgramKilled, p.externalCtx.Err())
+		} else if err == nil && p.ctx.Err() != nil {
+			// Return only that the program was killed (not the internal mechanism).
+			// The user does not know or need to care about the internal program context.
+			err = ErrProgramKilled
+		} else {
+			// Return that the program was killed and also the error that caused it.
+			err = fmt.Errorf("%w: %w", ErrProgramKilled, err)
+		}
+	} else {
+		// Graceful shutdown of the program (not killed):
 		// Ensure we rendered the final state of the model.
 		p.render(model)
 	}
@@ -1068,9 +1115,6 @@
 		}
 
 		_ = p.restoreTerminalState()
-		if !kill {
-			p.finished <- struct{}{}
-		}
 
 		// Print a final newline to ensure the terminal prompt is on a new line.
 		p.execute("\r\n")
@@ -1079,12 +1123,15 @@
 
 // recoverFromPanic recovers from a panic, prints the stack trace, and restores
 // the terminal to a usable state.
-func (p *Program) recoverFromPanic() {
-	if r := recover(); r != nil {
-		p.shutdown(true)
-		fmt.Printf("Caught panic:\n\n%s\n\nRestoring terminal...\n\n", r)
-		debug.PrintStack()
+func (p *Program) recoverFromPanic(r interface{}) {
+	select {
+	case p.errs <- ErrProgramPanic:
+	default:
 	}
+	p.cancel() // Just in case a previous shutdown has failed.
+	p.shutdown(true)
+	fmt.Printf("Caught panic:\n\n%s\n\nRestoring terminal...\n\n", r)
+	debug.PrintStack()
 }
 
 // ReleaseTerminal restores the original terminal state and cancels the input