Try to respond to signals sent to elvish-stub.

Doesn't always work, but the behavior is consistent in a session (if it works,
then it works in this session; vice versa). Likely some race in startup code.

eval/builtin_func.go

@@ -109,6 +109,7 @@ var (
 	ErrStoreNotConnected = errors.New("store not connected")
 	ErrNoMatchingDir     = errors.New("no matching directory")
 	ErrNotInSameGroup    = errors.New("not in the same process group")
+	ErrInterrupted       = errors.New("interrupted")
 )
 
 var (
@@ -638,7 +639,12 @@ func fg(ec *EvalCtx, pids ...int) {
 }
 
 func _sleep(ec *EvalCtx, t float64) {
-	time.Sleep(time.Duration(t) * time.Second)
+	d := time.Duration(float64(time.Second) * t)
+	select {
+	case <-ec.intCh:
+		throw(ErrInterrupted)
+	case <-time.After(d):
+	}
 }
 
 func _stack(ec *EvalCtx) {

eval/eval.go

@@ -36,6 +36,7 @@ type Evaler struct {
 	modules map[string]Namespace
 	store   *store.Store
 	Stub    *stub.Stub
+	intCh   <-chan struct{}
 }
 
 // EvalCtx maintains an Evaler along with its runtime context. After creation
@@ -56,7 +57,7 @@ func (ec *EvalCtx) evaling(n parse.Node) {
 
 // NewEvaler creates a new Evaler.
 func NewEvaler(st *store.Store) *Evaler {
-	ev := &Evaler{nil, map[string]Namespace{}, st, nil}
+	ev := &Evaler{nil, map[string]Namespace{}, st, nil, nil}
 
 	// Construct initial global namespace
 	pid := String(strconv.Itoa(syscall.Getpid()))
@@ -180,6 +181,35 @@ func (ev *Evaler) EvalInteractive(text string, n *parse.Chunk) error {
 		if err != nil {
 			fmt.Println("failed to put stub in foreground:", err)
 		}
+
+		intCh := make(chan struct{})
+		cancelCh := make(chan struct{})
+	exhaustSigs:
+		for {
+			select {
+			case <-ev.Stub.Signals():
+			default:
+				break exhaustSigs
+			}
+		}
+		go func() {
+			sigch := ev.Stub.Signals()
+			for {
+				select {
+				case sig := <-sigch:
+					fmt.Println(sig)
+					if sig == syscall.SIGINT {
+						close(intCh)
+						return
+					}
+				case <-cancelCh:
+					return
+				}
+			}
+		}()
+		defer close(cancelCh)
+		ev.intCh = intCh
+		defer func() { ev.intCh = nil }()
 	}
 
 	err := ev.Eval("[interactive]", text, n, ports)

stub/stub.go

@@ -116,10 +116,10 @@ func relaySignals(reader io.Reader, sigch chan<- os.Signal) {
 		var signum int
 		_, err := fmt.Fscanf(reader, "%d", &signum)
 		if err != nil {
-			// XXX Swallow error.
-			return
+			sigch <- BadSignal{err}
+		} else {
+			sigch <- syscall.Signal(signum)
 		}
-		sigch <- syscall.Signal(signum)
 	}
 }