cilium/cilium · error

formatting generated code: %w

Error message

formatting generated code: %w

What it means

The rendered template output is passed through go/format's format.Source to produce gofmt-clean Go code. This error wraps format.Source failing, which means the generated maps_generated.go content is not syntactically valid Go. The template emitted code the Go parser rejects.

Source

Thrown at tools/dpgen/maps.go:174

	b := bytes.Buffer{}
	if err := tpl.Execute(&b, struct {
		Package   string
		BTFFile   string
		OuterMaps []*ebpf.MapSpec
		AllMaps   []*ebpf.MapSpec
	}{
		pkg,
		mapKVFile,
		sorted(outer),
		sorted(all),
	}); err != nil {
		return fmt.Errorf("executing template: %w", err)
	}

	formatted, err := format.Source(b.Bytes())
	if err != nil {
		return fmt.Errorf("formatting generated code: %w", err)
	}

	if _, err := w.Write(formatted); err != nil {
		return fmt.Errorf("writing formatted code: %w", err)
	}

	return nil
}

func renderMapSpecsTest(w io.Writer, pkg string) error {
	tpl, err := template.New("mapSpecTest").Parse(mapSpecTestTpl)
	if err != nil {
		return fmt.Errorf("parsing test template: %w", err)
	}

	if err := tpl.Execute(w, struct{ Package string }{pkg}); err != nil {
		return fmt.Errorf("executing test template: %w", err)
	}

View on GitHub (pinned to ac7b90affa)

Solutions

1. Inspect the wrapped error — format.Source reports the exact line/column of the syntax error
2. Dump the unformatted buffer (temporarily skip format.Source) and examine the generated code around the reported position
3. Fix mapSpecTpl or the camelCase helper to emit valid Go identifiers for the offending map/typename
4. Re-run dpgen maps to regenerate and confirm it formats cleanly

Example fix

// before (helper output "4kHugePages" -> invalid identifier)
var Specs4kHugePages ... // syntax error
// after: prefix identifiers in camelCase helper or template so output is e.g. Specs4kHugePagesMap

// Validate identifiers the generator would emit
for name := range mapNames {
	id := camelCase(name)
	if id == "" || !token.IsIdentifier(id) {
		return fmt.Errorf("map %q renders invalid Go identifier %q", name, id)
	}
}

if err := runMaps(cmd, args); err != nil {
	if strings.Contains(err.Error(), "formatting generated code") {
		log.Fatalf("generated code invalid; dump buffer before format.Source to inspect: %v", err)
	}
	return err
}

When it happens

Trigger: The rendered mapSpecTpl output contains a syntax error — typically caused by template changes emitting invalid Go, malformed identifiers produced by camelCase on unusual map names, or empty/odd map data producing degenerate declarations.

Common situations: Developers editing mapSpecTpl and emitting unbalanced braces or invalid declarations; a map/typename combination whose camelCased identifier is not a valid Go identifier (e.g. starting with a digit); new BPF type names with characters Go cannot represent.

Related errors

• generating config struct: %w
• writing util file: %w
• writing header: %w
• external types needed but types package is empty
• writing imports: %w

AI-assisted analysis of cilium/cilium@ac7b90affa (2026-08-31). Data as JSON: /api/errors/a909902dcec53a58. Report an issue: GitHub.