fix: detect terminal size after exec

Based on @knz's work in #499, but slightly supersedes this change.

A little more coupling in the resize handling, but a lot less code
& logic repetition.

signals_unix.go

@@ -4,18 +4,15 @@
 package tea
 
 import (
-	"context"
 	"os"
 	"os/signal"
 	"syscall"
-
-	"golang.org/x/term"
 )
 
 // listenForResize sends messages (or errors) when the terminal resizes.
 // Argument output should be the file descriptor for the terminal; usually
 // os.Stdout.
-func listenForResize(ctx context.Context, output *os.File, msgs chan Msg, errs chan error, done chan struct{}) {
+func (p *Program) listenForResize(done chan struct{}) {
 	sig := make(chan os.Signal, 1)
 	signal.Notify(sig, syscall.SIGWINCH)
 
@@ -26,20 +23,11 @@ func listenForResize(ctx context.Context, output *os.File, msgs chan Msg, errs c
 
 	for {
 		select {
-		case <-ctx.Done():
+		case <-p.ctx.Done():
 			return
 		case <-sig:
 		}
 
-		w, h, err := term.GetSize(int(output.Fd()))
-		if err != nil {
-			errs <- err
-		}
-
-		select {
-		case <-ctx.Done():
-			return
-		case msgs <- WindowSizeMsg{w, h}:
-		}
+		p.checkResize()
 	}
 }

signals_windows.go

@@ -10,8 +10,6 @@ import (
 
 // listenForResize is not available on windows because windows does not
 // implement syscall.SIGWINCH.
-func listenForResize(ctx context.Context, output *os.File, msgs chan Msg,
-	errs chan error, done chan struct{},
-) {
+func (p *Program) listenForResize(done chan struct{}) {
 	close(done)
 }

tea.go

@@ -24,7 +24,6 @@ import (
 	isatty "github.com/mattn/go-isatty"
 	"github.com/muesli/cancelreader"
 	"github.com/muesli/termenv"
-	"golang.org/x/term"
 )
 
 // ErrProgramKilled is returned by [Program.Run] when the program got killed.
@@ -205,20 +204,10 @@ func (p *Program) handleResize() chan struct{} {
 
 	if f, ok := p.output.TTY().(*os.File); ok && isatty.IsTerminal(f.Fd()) {
 		// Get the initial terminal size and send it to the program.
-		go func() {
-			w, h, err := term.GetSize(int(f.Fd()))
-			if err != nil {
-				p.errs <- err
-			}
-
-			select {
-			case <-p.ctx.Done():
-			case p.msgs <- WindowSizeMsg{w, h}:
-			}
-		}()
+		go p.checkResize()
 
 		// Listen for window resizes.
-		go listenForResize(p.ctx, f, p.msgs, p.errs, ch)
+		go p.listenForResize(ch)
 	} else {
 		close(ch)
 	}
@@ -574,6 +563,12 @@ func (p *Program) RestoreTerminal() error {
 		go p.Send(repaintMsg{})
 	}
 
+	// If the output is a terminal, it may have been resized while another
+	// process was at the foreground, in which case we may not have received
+	// SIGWINCH. Detect any size change now and propagate the new size as
+	// needed.
+	go p.checkResize()
+
 	return nil
 }
 

tty.go

@@ -3,9 +3,12 @@ package tea
 import (
 	"errors"
 	"io"
+	"os"
 	"time"
 
+	isatty "github.com/mattn/go-isatty"
 	"github.com/muesli/cancelreader"
+	"golang.org/x/term"
 )
 
 func (p *Program) initTerminal() error {
@@ -76,7 +79,10 @@ func (p *Program) readLoop() {
 		msgs, err := readInputs(p.cancelReader)
 		if err != nil {
 			if !errors.Is(err, io.EOF) && !errors.Is(err, cancelreader.ErrCanceled) {
-				p.errs <- err
+				select {
+				case <-p.ctx.Done():
+				case p.errs <- err:
+				}
 			}
 
 			return
@@ -98,3 +104,28 @@ func (p *Program) waitForReadLoop() {
 		// though it was not able to cancel the read.
 	}
 }
+
+// checkResize detects the current size of the output and informs the program
+// via a WindowSizeMsg.
+func (p *Program) checkResize() {
+	f, ok := p.output.TTY().(*os.File)
+	if !ok || !isatty.IsTerminal(f.Fd()) {
+		// can't query window size
+		return
+	}
+
+	w, h, err := term.GetSize(int(f.Fd()))
+	if err != nil {
+		select {
+		case <-p.ctx.Done():
+		case p.errs <- err:
+		}
+
+		return
+	}
+
+	p.Send(WindowSizeMsg{
+		Width:  w,
+		Height: h,
+	})
+}