Turn ClientSnapshot.IsPromise into a method.

Single source of truth and all that.

capability.go

@@ -565,14 +565,8 @@ func (c Client) WeakRef() WeakClient {
 // Snapshot reads the current state of the client.  It returns the zero
 // ClientSnapshot if c is nil, has resolved to null, or has been released.
 func (c Client) Snapshot() ClientSnapshot {
-	h, resolved, _ := c.startCall()
-	if h == nil {
-		return ClientSnapshot{}
-	}
-	return ClientSnapshot{
-		hook:      h,
-		IsPromise: !resolved,
-	}
+	h, _, _ := c.startCall()
+	return ClientSnapshot{hook: h}
 }
 
 // A Brand is an opaque value used to identify a capability.
@@ -585,15 +579,21 @@ type Brand struct {
 // redirect to point at the resolution.
 type ClientSnapshot struct {
 	hook *rc.Ref[clientHook]
-	// IsPromise is true if the client was an unresolved promise when
-	// this snapshot was taken.
-	IsPromise bool
 }
 
 func (cs ClientSnapshot) IsValid() bool {
 	return cs.hook.IsValid()
 }
 
+// IsPromise returns true if the snapshot is a promise.
+func (cs ClientSnapshot) IsPromise() bool {
+	if cs.hook == nil {
+		return false
+	}
+	_, ret := cs.hook.Value().resolution.Get()
+	return ret
+}
+
 // Send implements ClientHook.Send
 func (cs ClientSnapshot) Send(ctx context.Context, s Send) (*Answer, ReleaseFunc) {
 	return cs.hook.Value().Send(ctx, s)

capability_test.go

@@ -25,7 +25,7 @@ func TestClient(t *testing.T) {
 		t.Error("new client is not valid")
 	}
 	state := c.Snapshot()
-	if state.IsPromise {
+	if state.IsPromise() {
 		t.Error("c.State().IsPromise = true; want false")
 	}
 	if state.Brand().Value != int(42) {
@@ -84,7 +84,7 @@ func TestReleasedClient(t *testing.T) {
 	if state.Brand().Value != nil {
 		t.Errorf("c.Snapshot().Brand().Value = %#v; want <nil>", state.Brand().Value)
 	}
-	if state.IsPromise {
+	if state.IsPromise() {
 		t.Error("c.Snapshot().IsPromise = true; want false")
 	}
 	state.Release()
@@ -191,7 +191,7 @@ func TestNullClient(t *testing.T) {
 			if state.Brand().Value != nil {
 				t.Errorf("c.Snapshot().Brand() = %#v; want <nil>", state.Brand())
 			}
-			if state.IsPromise {
+			if state.IsPromise() {
 				t.Error("c.Snapshot().IsPromise = true; want false")
 			}
 			state.Release()
@@ -237,7 +237,7 @@ func TestPromisedClient(t *testing.T) {
 	if state.Brand().Value != int(111) {
 		t.Errorf("before resolution, ca.Snapshot().Brand().Value = %#v; want 111", state.Brand().Value)
 	}
-	if !state.IsPromise {
+	if !state.IsPromise() {
 		t.Error("before resolution, ca.Snapshot().IsPromise = false; want true")
 	}
 	state.Release()
@@ -259,7 +259,7 @@ func TestPromisedClient(t *testing.T) {
 	if state.Brand().Value != int(222) {
 		t.Errorf("after resolution, ca.Snapshot().Brand().Value = %#v; want 222", state.Brand().Value)
 	}
-	if state.IsPromise {
+	if state.IsPromise() {
 		t.Error("after resolution, ca.Snapshot().IsPromise = true; want false")
 	}
 	state.Release()

rpc/export.go

@@ -172,7 +172,7 @@ func (c *lockedConn) sendCap(d rpccp.CapDescriptor, client capnp.Client) (_ expo
 		ee = &expent{
 			client:    client.AddRef(),
 			wireRefs:  1,
-			isPromise: state.IsPromise,
+			isPromise: state.IsPromise(),
 			cancel:    func() {},
 		}
 		id = exportID(c.lk.exportID.next())