Function RegisterContextTag

log/context.go:137–163

RegisterContextTag registers a contextual tag that can be used by SetContextTemplate. Re-registering a tag replaces the existing tag function. Registration is package-global; prefer ContextConfig.CustomTags for per-application overrides. The reserved TagContextValue tag cannot be registered.

(tag string, fn ContextTagFunc)

// prefer ContextConfig.CustomTags for per-application overrides. The reserved TagContextValue
// tag cannot be registered.
func RegisterContextTag(tag string, fn ContextTagFunc) error {
	if tag == "" || fn == nil {
		return ErrContextTagInvalid
	}
	if tag == TagContextValue {
		return ErrContextTagReserved
	}

	contextMu.Lock()
	defer contextMu.Unlock()

	tags := maps.Clone(contextTags)
	tags[tag] = fn

	var tmpl *logtemplate.Template[any, ContextData]
	if contextFormat != "" {
		var err error
		tmpl, err = logtemplate.Build[any, ContextData](contextFormat, tags)
		if err != nil {
			return err
		}
	}

	contextTags = tags
	contextTemplate.Store(tmpl)
	return nil
}

// MustRegisterContextTag registers a contextual tag and panics if registration fails.
func MustRegisterContextTag(tag string, fn ContextTagFunc) {