[featuregate] Deprecate NewFlag in favor of RegisterFlags

.chloggen/mx-psi_featuregate-futureproof.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: deprecation
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: featuregate
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Deprecate `featuregate.NewFlag` in favor of `featuregate.Registry`'s `RegisterFlags` method
+
+# One or more tracking issues or pull requests related to the change
+issues: [8727]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [api]

featuregate/flag.go

@@ -10,11 +10,31 @@
 	"go.uber.org/multierr"
 )
 
+const (
+	featureGatesFlag            = "feature-gates"
+	featureGatesFlagDescription = "Comma-delimited list of feature gate identifiers. Prefix with '-' to disable the feature. '+' or no prefix will enable the feature."
+)
+
 // NewFlag returns a flag.Value that directly applies feature gate statuses to a Registry.
+// Deprecated: Use Registry's RegisterFlags method instead.
 func NewFlag(reg *Registry) flag.Value {
+	return newFeatureGateValue(reg)
+}
+
+func newFeatureGateValue(reg *Registry) flag.Value {
 	return &flagValue{reg: reg}
 }
 
+// RegisterFlagsOption is an option for RegisterFlags.
+type RegisterFlagsOption interface {
+	private()
+}
+
+// RegisterFlags that directly applies feature gate statuses to a Registry.
+func (r *Registry) RegisterFlags(flagSet *flag.FlagSet, _ ...RegisterFlagsOption) {
+	flagSet.Var(newFeatureGateValue(r), featureGatesFlag, featureGatesFlagDescription)
+}
+
 // flagValue implements the flag.Value interface and directly applies feature gate statuses to a Registry.
 type flagValue struct {
 	reg *Registry

featuregate/flag_test.go

@@ -4,6 +4,7 @@
 package featuregate
 
 import (
+	"flag"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -113,18 +114,21 @@ func TestNewFlag(t *testing.T) {
 			reg.MustRegister("beta", StageBeta)
 			reg.MustRegister("deprecated", StageDeprecated, WithRegisterToVersion("1.0.0"))
 			reg.MustRegister("stable", StageStable, WithRegisterToVersion("1.0.0"))
-			v := NewFlag(reg)
+			fs := flag.NewFlagSet("test", flag.ContinueOnError)
+			reg.RegisterFlags(fs)
+			registrationFlag := fs.Lookup(featureGatesFlag)
+			require.NotNil(t, registrationFlag)
 			if tt.expectedSetErr {
-				require.Error(t, v.Set(tt.input))
+				require.Error(t, registrationFlag.Value.Set(tt.input))
 			} else {
-				require.NoError(t, v.Set(tt.input))
+				require.NoError(t, registrationFlag.Value.Set(tt.input))
 			}
 			got := map[string]bool{}
 			reg.VisitAll(func(g *Gate) {
 				got[g.ID()] = g.IsEnabled()
 			})
 			assert.Equal(t, tt.expected, got)
-			assert.Equal(t, tt.expectedStr, v.String())
+			assert.Equal(t, tt.expectedStr, registrationFlag.Value.String())
 		})
 	}
 }

otelcol/flags.go

@@ -12,8 +12,7 @@ import (
 )
 
 const (
-	configFlag       = "config"
-	featureGatesFlag = "feature-gates"
+	configFlag = "config"
 )
 
 type configFlagValue struct {
@@ -50,9 +49,7 @@ func flags(reg *featuregate.Registry) *flag.FlagSet {
 			return nil
 		})
 
-	flagSet.Var(featuregate.NewFlag(reg), featureGatesFlag,
-		"Comma-delimited list of feature gate identifiers. Prefix with '-' to disable the feature. '+' or no prefix will enable the feature.")
-
+	reg.RegisterFlags(flagSet)
 	return flagSet
 }