.github: add a staticcheck action (#326)

Add a staticcheck step to the lint job of the Test workflow, and fix
reported diagnostics.

.github/workflows/test.yml

@@ -30,6 +30,10 @@ jobs:
           echo "All Go files are properly formatted"
       - name: Run Go vet
         run: go vet ./...
+      - name: Run staticcheck
+        uses: dominikh/staticcheck-action@v1
+        with:
+          version: "latest"
 
   test:
     runs-on: ubuntu-latest

internal/jsonrpc2/conn.go

@@ -719,10 +719,10 @@ func (c *Connection) processResult(from any, req *incomingRequest, result any, e
 		} else if err != nil {
 			err = fmt.Errorf("%w: %q notification failed: %v", ErrInternal, req.Method, err)
 		}
-		if err != nil {
-			// TODO: can/should we do anything with this error beyond writing it to the event log?
-			// (Is this the right label to attach to the log?)
-		}
+	}
+	if err != nil {
+		// TODO: can/should we do anything with this error beyond writing it to the event log?
+		// (Is this the right label to attach to the log?)
 	}
 
 	// Cancel the request to free any associated resources.

mcp/client.go

@@ -178,10 +178,6 @@ type clientSessionState struct {
 
 func (cs *ClientSession) InitializeResult() *InitializeResult { return cs.state.InitializeResult }
 
-func (cs *ClientSession) setConn(c Connection) {
-	cs.mcpConn = c
-}
-
 func (cs *ClientSession) ID() string {
 	if c, ok := cs.mcpConn.(hasSessionID); ok {
 		return c.SessionID()

mcp/streamable.go

@@ -121,7 +121,7 @@ func (h *StreamableHTTPHandler) ServeHTTP(w http.ResponseWriter, req *http.Reque
 	var transport *StreamableServerTransport
 	if id := req.Header.Get(sessionIDHeader); id != "" {
 		h.mu.Lock()
-		transport, _ = h.transports[id]
+		transport = h.transports[id]
 		h.mu.Unlock()
 		if transport == nil {
 			http.Error(w, "session not found", http.StatusNotFound)
@@ -288,9 +288,6 @@ type streamableServerConn struct {
 	jsonResponse bool
 	eventStore   EventStore
 
-	lastStreamID atomic.Int64 // last stream ID used, atomically incremented
-
-	opts     StreamableServerTransportOptions
 	incoming chan jsonrpc.Message // messages from the client to the server
 	done     chan struct{}
 

mcp/streamable_test.go

@@ -539,10 +539,10 @@ func TestStreamableServerTransport(t *testing.T) {
 		},
 		{
 			name: "background",
-			tool: func(t *testing.T, ctx context.Context, ss *ServerSession) {
+			tool: func(t *testing.T, _ context.Context, ss *ServerSession) {
 				// Perform operations on a background context, and ensure the client
 				// receives it.
-				ctx = context.Background()
+				ctx := context.Background()
 				if err := ss.NotifyProgress(ctx, &ProgressNotificationParams{}); err != nil {
 					t.Errorf("Notify failed: %v", err)
 				}