Initial MCP Roots support

mcpserver/roots.go

@@ -0,0 +1,102 @@
+package mcpserver
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"strings"
+	"sync"
+
+	"github.com/mark3labs/mcp-go/mcp"
+	"github.com/mark3labs/mcp-go/server"
+)
+
+// clientRoots holds the roots provided by the client
+// this assumes a single client, which may go out the window when we add support for streaming http.
+var (
+	clientRoots   []mcp.Root
+	clientRootsMu sync.RWMutex
+)
+
+// sendRootsListRequest sends a roots/list request to the client
+func sendRootsListRequest(ctx context.Context, session server.ClientSession) {
+	if session == nil {
+		return
+	}
+
+	// Send roots/list request as a notification
+	// Note: In a proper implementation, this would be a request-response
+	// but for now we'll send as notification and handle response separately
+	notification := mcp.JSONRPCNotification{
+		JSONRPC: "2.0",
+		Notification: mcp.Notification{
+			Method: "roots/list",
+			Params: mcp.NotificationParams{},
+		},
+	}
+
+	select {
+	case session.NotificationChannel() <- notification:
+		slog.Info("Requested roots/list from client")
+	case <-ctx.Done():
+		return
+	}
+}
+
+// updateClientRoots parses roots from notification params and updates the global clientRoots
+func updateClientRoots(notification mcp.JSONRPCNotification) int {
+	if notification.Params.AdditionalFields == nil {
+		return 0
+	}
+	rootsData, ok := notification.Params.AdditionalFields["roots"].([]any)
+	if !ok {
+		return 0
+	}
+
+	newRoots := make([]mcp.Root, 0, len(rootsData))
+	for _, rootData := range rootsData {
+		if rootMap, ok := rootData.(map[string]any); ok {
+			root := mcp.Root{}
+			if uri, ok := rootMap["uri"].(string); ok {
+				root.URI = uri
+			}
+			if name, ok := rootMap["name"].(string); ok {
+				root.Name = name
+			}
+			newRoots = append(newRoots, root)
+		}
+	}
+
+	clientRootsMu.Lock()
+	clientRoots = newRoots
+	clientRootsMu.Unlock()
+
+	return len(newRoots)
+}
+
+// repoOpenErrorMessage provides helpful error messages when repository opening fails
+func repoOpenErrorMessage(source string, originalErr error) error {
+	baseMsg := fmt.Sprintf("failed to open repository '%s'", source)
+
+	// If we have client roots, suggest them
+	clientRootsMu.RLock()
+	defer clientRootsMu.RUnlock()
+
+	if len(clientRoots) > 0 {
+		baseMsg += "\n\nAvailable roots from client:"
+		for _, root := range clientRoots {
+			uri := root.URI
+			uri = strings.TrimPrefix(uri, "file://")
+			if root.Name != "" {
+				baseMsg += fmt.Sprintf("\n  - %s (%s)", uri, root.Name)
+			} else {
+				baseMsg += fmt.Sprintf("\n  - %s", uri)
+			}
+		}
+		return fmt.Errorf("%s: %w", baseMsg, originalErr)
+	}
+
+	// Fallback: suggest common patterns
+	baseMsg += "\n\nTry using:\n  - '.' for current directory\n  - An absolute path to your git repository"
+	return fmt.Errorf("%s: %w", baseMsg, originalErr)
+}

mcpserver/tools.go

@@ -57,12 +57,44 @@ type Tool struct {
 }
 
 func RunStdioServer(ctx context.Context, dag *dagger.Client) error {
+	// Create hooks to handle initialization and roots
+	hooks := &server.Hooks{}
+
+	// Add hook to check for roots capability and request initial roots
+	hooks.AddAfterInitialize(func(ctx context.Context, id any, message *mcp.InitializeRequest, result *mcp.InitializeResult) {
+		if message.Params.Capabilities.Roots != nil {
+			slog.Info("Client supports roots capability", "listChanged", message.Params.Capabilities.Roots.ListChanged)
+
+			// Get the client session and send roots/list request
+			if session := server.ClientSessionFromContext(ctx); session != nil {
+				sendRootsListRequest(ctx, session)
+			}
+		} else {
+			slog.Info("Client does not support roots capability")
+		}
+	})
+
 	s := server.NewMCPServer(
 		"Dagger",
 		"1.0.0",
 		server.WithInstructions(rules.AgentRules),
+		server.WithHooks(hooks),
 	)
 
+	// Add notification handler for roots updates from client
+	s.AddNotificationHandler("notifications/roots/list_changed", func(ctx context.Context, notification mcp.JSONRPCNotification) {
+		slog.Info("Received notifications/roots/list_changed from client")
+		count := updateClientRoots(notification)
+		slog.Info("Updated client roots", "count", count)
+	})
+
+	// Add response handler for roots/list responses
+	s.AddNotificationHandler("roots/list", func(ctx context.Context, notification mcp.JSONRPCNotification) {
+		slog.Info("Received roots/list response from client")
+		count := updateClientRoots(notification)
+		slog.Info("Updated client roots from response", "count", count)
+	})
+
 	for _, t := range tools {
 		s.AddTool(t.Definition, wrapToolWithClient(t, dag).Handler)
 	}
@@ -241,7 +273,7 @@ var EnvironmentOpenTool = &Tool{
 func GetEnvironmentFromSource(ctx context.Context, dag *dagger.Client, source, envID string) (*environment.Environment, error) {
 	repo, err := repository.Open(ctx, source)
 	if err != nil {
-		return nil, err
+		return nil, repoOpenErrorMessage(source, err)
 	}
 
 	env, err := repo.Get(ctx, dag, envID)
@@ -320,7 +352,7 @@ You MUST tell the user: To include these changes in the environment, they need t
 func CreateEnvironment(ctx context.Context, dag *dagger.Client, source, title, explanation string) (*repository.Repository, *environment.Environment, error) {
 	repo, err := repository.Open(ctx, source)
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, repoOpenErrorMessage(source, err)
 	}
 
 	env, err := repo.Create(ctx, dag, title, explanation)