Improve error reporting for Populate()

Show the pretty-printed error from populating the object graph
in PrintObjects() and PrintDotGraph(). Add the ErrPopulate so
we can add special casing for it in cilium/cilium to also do the
pretty-printing of the error there.

Will look like this:

2025/03/07 11:30:13 ERROR Invoke failed error="missing type:\n\t- resource.Resource[*github.com/cilium/cilium/pkg/k8s/slim/k8s/api/core/v1.Service] (did you mean to Provide it?)" function="cmd.configureAPIServer (cmd/cells.go:330)"
Failed to populate object graph:
could not build arguments for function "github.com/cilium/cilium/daemon/cmd".configureAPIServer
        /home/jussi/go/src/github.com/cilium/cilium/daemon/cmd/cells.go:330:
failed to build *server.Server:
could not build arguments for function "github.com/cilium/cilium/api/v1/server".newForCell
        /home/jussi/go/src/github.com/cilium/cilium/api/v1/server/server.go:206:
failed to build *restapi.CiliumAPIAPI:
could not build arguments for function "github.com/cilium/cilium/api/v1/server".newAPI
        /home/jussi/go/src/github.com/cilium/cilium/api/v1/server/server.go:125:
failed to build endpoint.DeleteEndpointHandler:
could not build arguments for function "github.com/cilium/cilium/daemon/cmd".ciliumAPIHandlers
        /home/jussi/go/src/github.com/cilium/cilium/daemon/cmd/api_handlers.go:81:
failed to build promise.Promise[*github.com/cilium/cilium/daemon/cmd.Daemon]:
could not build arguments for function "github.com/cilium/cilium/daemon/cmd".newDaemonPromise
        /home/jussi/go/src/github.com/cilium/cilium/daemon/cmd/daemon_main.go:1585:
failed to build *clustermesh.ClusterMesh:
could not build arguments for function "github.com/cilium/cilium/pkg/clustermesh".NewClusterMesh
        /home/jussi/go/src/github.com/cilium/cilium/pkg/clustermesh/clustermesh.go:133:
failed to build *dial.ServiceResolver:
missing dependencies for function "github.com/cilium/cilium/pkg/dial".newServiceResolver
        /home/jussi/go/src/github.com/cilium/cilium/pkg/dial/resolver.go:43:
missing type:
        - resource.Resource[*github.com/cilium/cilium/pkg/k8s/slim/k8s/api/core/v1.Service] (did you mean to Provide it?)

Signed-off-by: Jussi Maki <[email protected]>

Author: joamaki

cell/invoke.go

@@ -49,7 +49,7 @@ func (inv *invoker) invoke(log *slog.Logger, cont container, logThreshold time.D
 		defer inv.funcs[i].infoMu.Unlock()
 
 		if err := cont.Invoke(nf.fn, opts...); err != nil {
-			log.Error("Invoke failed", "error", err, "function", nf.name)
+			log.Error("Invoke failed", "error", dig.RootCause(err), "function", nf.name)
 			return err
 		}
 		d := time.Since(t0)

command.go

@@ -14,21 +14,23 @@ import (
 // command can be used to inspect the dependency graph.
 func (h *Hive) Command() *cobra.Command {
 	cmd := &cobra.Command{
-		Use:   "hive",
-		Short: "Inspect the hive",
-		Run: func(cmd *cobra.Command, args []string) {
-			h.PrintObjects(os.Stdout, slog.Default())
+		Use:          "hive",
+		Short:        "Inspect the hive",
+		SilenceUsage: true,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return h.PrintObjects(os.Stdout, slog.Default())
 		},
 		TraverseChildren: false,
 	}
 	h.RegisterFlags(cmd.PersistentFlags())
 
 	cmd.AddCommand(
 		&cobra.Command{
-			Use:   "dot-graph",
-			Short: "Output the dependencies graph in graphviz dot format",
-			Run: func(cmd *cobra.Command, args []string) {
-				h.PrintDotGraph()
+			Use:          "dot-graph",
+			Short:        "Output the dependencies graph in graphviz dot format",
+			SilenceUsage: true,
+			RunE: func(cmd *cobra.Command, args []string) error {
+				return h.PrintDotGraph()
 			},
 			TraverseChildren: false,
 		})

hive.go

@@ -229,6 +229,9 @@ func (h *Hive) Run(log *slog.Logger) error {
 
 	var errs error
 	if err := h.Start(log, startCtx); err != nil {
+		if errors.Is(err, ErrPopulate{}) {
+			return err
+		}
 		errs = errors.Join(errs, fmt.Errorf("failed to start: %w", err))
 	}
 
@@ -326,12 +329,27 @@ func (h *Hive) AppendInvoke(invoke func(*slog.Logger, time.Duration) error) {
 	h.invokes = append(h.invokes, invoke)
 }
 
+type ErrPopulate struct {
+	err error
+}
+
+// Error implements error.
+func (e ErrPopulate) Error() string {
+	return fmt.Sprintf("failed to populate object graph: %s", dig.RootCause(e.err))
+}
+
+func (e ErrPopulate) Pretty() string {
+	return fmt.Sprintf("Failed to populate object graph:\n%+v", e.err)
+}
+
+var _ error = ErrPopulate{}
+
 // Start starts the hive. The context allows cancelling the start.
 // If context is cancelled and the start hooks do not respect the cancellation
 // then after 5 more seconds the process will be terminated forcefully.
 func (h *Hive) Start(log *slog.Logger, ctx context.Context) error {
 	if err := h.Populate(log); err != nil {
-		return err
+		return ErrPopulate{err}
 	}
 
 	defer close(h.fatalOnTimeout(ctx))
@@ -393,9 +411,11 @@ func (h *Hive) Shutdown(opts ...ShutdownOption) {
 	}
 }
 
-func (h *Hive) PrintObjects(w io.Writer, log *slog.Logger) {
+func (h *Hive) PrintObjects(w io.Writer, log *slog.Logger) error {
 	if err := h.Populate(log); err != nil {
-		panic(fmt.Sprintf("Failed to populate object graph: %s", err))
+		err := ErrPopulate{err}
+		fmt.Fprintf(w, "ERROR: %s\n", err.Pretty())
+		return err
 	}
 
 	fmt.Fprintf(w, "Cells:\n\n")
@@ -405,16 +425,16 @@ func (h *Hive) PrintObjects(w io.Writer, log *slog.Logger) {
 		fmt.Fprintln(w)
 	}
 	h.lifecycle.PrintHooks(w)
+	return nil
 }
 
-func (h *Hive) PrintDotGraph() {
+func (h *Hive) PrintDotGraph() error {
 	if err := h.Populate(slog.Default()); err != nil {
-		panic(fmt.Sprintf("Failed to populate object graph: %s", err))
-	}
-
-	if err := dig.Visualize(h.container, os.Stdout); err != nil {
-		panic(fmt.Sprintf("Failed to dig.Visualize(): %s", err))
+		err := ErrPopulate{err}
+		fmt.Fprintf(os.Stderr, "ERROR: %s\n", err.Pretty())
+		return err
 	}
+	return dig.Visualize(h.container, os.Stdout)
 }
 
 // getEnvName returns the environment variable to be used for the given option name.
@@ -434,10 +454,10 @@ func (h *Hive) ScriptCommands(log *slog.Logger) (map[string]script.Cmd, error) {
 	m["hive/stop"] = hiveStopCmd(h, log)
 
 	// Gather the commands from the hive.
-	h.container.Invoke(func(sc ScriptCmds) {
+	err := h.container.Invoke(func(sc ScriptCmds) {
 		for name, cmd := range sc.Map() {
 			m[name] = cmd
 		}
 	})
-	return m, nil
+	return m, err
 }

script.go

@@ -82,8 +82,8 @@ func hiveScriptCmd(h *Hive, log *slog.Logger) script.Cmd {
 				defer cancel()
 				return nil, h.Stop(log, ctx)
 			default:
-				h.PrintObjects(s.LogWriter(), log)
-				return nil, nil
+				err := h.PrintObjects(s.LogWriter(), log)
+				return nil, err
 			}
 		},
 	)