crowdsecurity/crowdsec · warning

ErrFeatureDeprecated

ErrFeatureDeprecated

Error message

the flag is deprecated

What it means

Sentinel error ErrFeatureDeprecated returned when enabling a feature whose State is DeprecatedState. The flag is still applied (Set sets it anyway), but callers should warn with feat.DeprecationMsg since the flag will be removed in a future release.

Source

Thrown at pkg/fflag/features.go:47

import (
	"errors"
	"fmt"
	"io"
	"os"
	"regexp"
	"sort"
	"strings"

	"github.com/goccy/go-yaml"
	"github.com/sirupsen/logrus"
)

var (
	ErrFeatureNameEmpty   = errors.New("name is empty")
	ErrFeatureNameCase    = errors.New("name is not lowercase")
	ErrFeatureNameInvalid = errors.New("invalid name (allowed a-z, 0-9, _, .)")
	ErrFeatureUnknown     = errors.New("unknown feature")
	ErrFeatureDeprecated  = errors.New("the flag is deprecated")
	ErrFeatureRetired     = errors.New("the flag is retired")
)

const (
	ActiveState     = iota // the feature can be enabled, and its description is logged (Info)
	DeprecatedState        // the feature can be enabled, and a deprecation message is logged (Warning)
	RetiredState           // the feature is ignored and a deprecation message is logged (Error)
)

type Feature struct {
	Name  string
	State int // active, deprecated, retired

	// Description should be a short sentence, explaining the feature.
	Description string

	// DeprecationMessage is used to inform the user of the behavior that has
	// been decided when the flag is/was finally retired.

View on GitHub (pinned to 909b515798)

Solutions

1. Read the DeprecationMsg logged at startup and migrate to the replacement flag or built-in behavior
2. Remove the deprecated flag from config.yaml / env since enabling it is now a no-op with warning
3. Plan upgrade: deprecated flags become retired (ignored) in later releases

Example fix

// before
feature-flags:
  old_flag_name: true
// after
# remove the entry; feature is on by default now

if feat, err := fflag.GetFeature(name); err == nil && feat.State == fflag.DeprecatedState { log.Warn("flag deprecated: " + feat.DeprecationMsg) }

if err := fflag.Set(name); errors.Is(err, fflag.ErrFeatureDeprecated) { log.Warnf("%s is deprecated: %s", name, feat.DeprecationMsg) }

When it happens

Trigger: Set, SetFromEnv or SetFromYaml called on a feature flagged DeprecatedState; e.g. FFLAGS-style env var naming a deprecated feature at startup.

Common situations: Config carried over from an older crowdsec where a feature was still active but is now deprecated; CI scripts setting deprecated flags programmatically.

Understand the failure class

Background: "is deprecated and will be removed" — deprecation warnings for old API names, keywords, and options, and how to migrate before the removal release — this error's family across 29 libraries.

Related errors

• ErrFeatureRetired
• ErrFeatureNameInvalid
• ErrFeatureUnknown
• feature flag '%s': %w
• failed to parse feature flags: %w

AI-assisted analysis of crowdsecurity/crowdsec@909b515798 (2026-09-06). Data as JSON: /api/errors/1b0d1d96b7c1f5fa. Report an issue: GitHub.