internal/lsp/protocol: actually handle cancellation delivery

CL 215738 didn't work because the canceller was embedded in the
serverHandler, which already had a Deliver method. Add it as an actual
handler instead.

Change-Id: I0c79f1bee67aa3b4da53d92547804de859f1938c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/216303
Run-TryBot: Heschi Kreinick <heschi@google.com>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

internal/jsonrpc2/jsonrpc2.go

@@ -233,7 +233,7 @@ func (r *Request) Reply(ctx context.Context, result interface{}, err error) erro
 		return fmt.Errorf("reply invoked more than once")
 	}
 	if r.IsNotify() {
-		return fmt.Errorf("reply not invoked with a valid call")
+		return fmt.Errorf("reply not invoked with a valid call: %v, %s", r.Method, r.Params)
 	}
 	// reply ends the handling phase of a call, so if we are not yet
 	// parallel we should be now. The go routine is allowed to continue

internal/lsp/protocol/protocol.go

@@ -23,12 +23,12 @@ const (
 type canceller struct{ jsonrpc2.EmptyHandler }
 
 type clientHandler struct {
-	canceller
+	jsonrpc2.EmptyHandler
 	client Client
 }
 
 type serverHandler struct {
-	canceller
+	jsonrpc2.EmptyHandler
 	server Server
 }
 
@@ -73,6 +73,7 @@ func NewClient(ctx context.Context, stream jsonrpc2.Stream, client Client) (cont
 	ctx = WithClient(ctx, client)
 	conn := jsonrpc2.NewConn(stream)
 	conn.AddHandler(&clientHandler{client: client})
+	conn.AddHandler(&canceller{})
 	return ctx, conn, &serverDispatcher{Conn: conn}
 }
 
@@ -81,6 +82,7 @@ func NewServer(ctx context.Context, stream jsonrpc2.Stream, server Server) (cont
 	client := &clientDispatcher{Conn: conn}
 	ctx = WithClient(ctx, client)
 	conn.AddHandler(&serverHandler{server: server})
+	conn.AddHandler(&canceller{})
 	return ctx, conn, client
 }