golang/go · error

no trace file supplied

Error message

no trace file supplied

What it means

trace.Start requires a destination file path; passing an empty string is rejected up front. This is the entry point backing the `go trace` (trace viewer) command's file handling.

Source

Thrown at src/cmd/go/internal/trace/trace.go:184

func (t *tracer) getNextFlowID() uint64 {
	return t.nextFlowID.Add(1)
}

// traceKey is the context key for tracing information. It is unexported to prevent collisions with context keys defined in
// other packages.
type traceKey struct{}

type traceContext struct {
	t   *tracer
	tid uint64
}

// Start starts a trace which writes to the given file.
func Start(ctx context.Context, file string) (context.Context, func() error, error) {
	traceStarted.Store(true)
	if file == "" {
		return nil, nil, errors.New("no trace file supplied")
	}
	f, err := os.Create(file)
	if err != nil {
		return nil, nil, err
	}
	t := &tracer{file: make(chan traceFile, 1)}
	sb := new(strings.Builder)
	t.file <- traceFile{
		f:   f,
		sb:  sb,
		enc: json.NewEncoder(sb),
	}
	ctx = context.WithValue(ctx, traceKey{}, traceContext{t: t})
	return ctx, t.Close, nil
}

type traceFile struct {
	f       *os.File

View on GitHub (pinned to b6b368adc5)

Solutions

  1. Supply a non-empty file path to trace.Start / the trace subcommand.
  2. Generate a trace first (runtime/trace.Start) if you don't have one yet.

Example fix

// before
ctx, stop, err := trace.Start(context.Background(), "")

// after
ctx, stop, err := trace.Start(context.Background(), "./trace.out")
Defensive patterns

Strategy: validation

Validate before calling

// Reject an empty trace file before calling Start.
func startTrace(file string) (context.Context, func() error, error) {
    if file == "" { return nil, nil, errors.New("provide a trace file path") }
    return trace.Start(context.Background(), file)
}

Type guard

null

Try / catch

null

Prevention

When it happens

Trigger: Calling trace.Start(ctx, "") directly, or invoking the trace subcommand without supplying a trace file argument.

Common situations: Forgot the file argument; scripting that passes an empty path; mis-parsed CLI flags.

Related errors

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/a3d7e2f7549b8cb5. Report an issue: GitHub.