Feature gate CLI flag and visibility changes (#4368)

* Expose feature gate registry type and its methods

Signed-off-by: Anthony J Mirabella <a9@aneurysm9.com>

* Add CLI flags for feature gates

Signed-off-by: Anthony J Mirabella <a9@aneurysm9.com>

* Add accessor for global feature gate registry

Signed-off-by: Anthony J Mirabella <a9@aneurysm9.com>

* add canonical import comment

Signed-off-by: Anthony J Mirabella <a9@aneurysm9.com>

* Revert "Add accessor for global feature gate registry"

This reverts commit 23c957c.

* Revert "Expose feature gate registry type and its methods"

This reverts commit df64ad2.

Signed-off-by: Anthony J Mirabella <a9@aneurysm9.com>

* Add CHANGELOG entry, update docblock for Flags()

Signed-off-by: Anthony J Mirabella <a9@aneurysm9.com>

CHANGELOG.md

@@ -12,6 +12,10 @@
 
 - Add semconv 1.7.0 and 1.8.0 (#4452)
 
+## 💡 Enhancements 💡
+
+- Added `feature-gates` CLI flag for controlling feature gate state. (#4368)
+
 ## v0.39.0 Beta
 
 ## 🛑 Breaking changes 🛑

service/command.go

@@ -18,6 +18,7 @@ import (
 	"github.com/spf13/cobra"
 
 	"go.opentelemetry.io/collector/config/configmapprovider"
+	"go.opentelemetry.io/collector/service/featuregate"
 )
 
 // NewCommand constructs a new cobra.Command using the given Collector.
@@ -28,6 +29,7 @@ func NewCommand(set CollectorSettings) *cobra.Command {
 		Version:      set.BuildInfo.Version,
 		SilenceUsage: true,
 		RunE: func(cmd *cobra.Command, args []string) error {
+			featuregate.Apply(featuregate.GetFlags())
 			if set.ConfigMapProvider == nil {
 				set.ConfigMapProvider = configmapprovider.NewDefault(getConfigFlag(), getSetFlag())
 			}

service/featuregate/flags.go

@@ -0,0 +1,96 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//       http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package featuregate // import "go.opentelemetry.io/collector/service/featuregate"
+
+import (
+	"flag"
+	"sort"
+	"strings"
+)
+
+const gatesListCfg = "feature-gates"
+
+var gatesList = FlagValue{}
+
+// Flags adds CLI flags for managing feature gates to the provided FlagSet
+// Feature gates can be configured with `--feature-gates=foo,-bar`.  This would
+// enable the `foo` feature gate and disable the `bar` feature gate.
+func Flags(flags *flag.FlagSet) {
+	flags.Var(
+		gatesList,
+		gatesListCfg,
+		"Comma-delimited list of feature gate identifiers. Prefix with '-' to disable the feature.  '+' or no prefix will enable the feature.")
+}
+
+// GetFlags returns the FlagValue used with Flags()
+func GetFlags() FlagValue {
+	return gatesList
+}
+
+var _ flag.Value = (*FlagValue)(nil)
+
+// FlagValue implements the flag.Value interface and provides a mechanism for applying feature
+// gate statuses to a Registry
+type FlagValue map[string]bool
+
+// String returns a string representing the FlagValue
+func (f FlagValue) String() string {
+	var t []string
+	for k, v := range f {
+		if v {
+			t = append(t, k)
+		} else {
+			t = append(t, "-"+k)
+		}
+	}
+
+	// Sort the list of identifiers for consistent results
+	sort.Strings(t)
+	return strings.Join(t, ",")
+}
+
+// Set applies the FlagValue encoded in the input string
+func (f FlagValue) Set(s string) error {
+	return f.SetSlice(strings.Split(s, ","))
+}
+
+// SetSlice applies the feature gate statuses in the input slice to the FlagValue
+func (f FlagValue) SetSlice(s []string) error {
+	for _, v := range s {
+		var id string
+		var val bool
+		switch v[0] {
+		case '-':
+			id = v[1:]
+			val = false
+		case '+':
+			id = v[1:]
+			val = true
+		default:
+			id = v
+			val = true
+		}
+
+		if _, exists := f[id]; exists {
+			// If the status has already been set, ignore it
+			// This allows CLI flags, which are processed first
+			// to take precedence over config settings
+			continue
+		}
+		f[id] = val
+	}
+
+	return nil
+}

service/featuregate/flags_test.go

@@ -0,0 +1,93 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//       http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package featuregate
+
+import (
+	"flag"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFlags(t *testing.T) {
+	fs := flag.NewFlagSet("test", flag.ContinueOnError)
+	Flags(fs)
+	assert.Equal(t, gatesList, fs.Lookup(gatesListCfg).Value)
+}
+
+func TestGetFlags(t *testing.T) {
+	assert.Equal(t, gatesList, GetFlags())
+}
+
+func TestFlagValue_basic(t *testing.T) {
+	for _, tc := range []struct {
+		name     string
+		expected string
+		input    FlagValue
+	}{
+		{
+			name:     "single item",
+			input:    FlagValue{"foo": true},
+			expected: "foo",
+		},
+		{
+			name:     "single disabled item",
+			input:    FlagValue{"foo": false},
+			expected: "-foo",
+		},
+		{
+			name:     "multiple items",
+			input:    FlagValue{"foo": true, "bar": false},
+			expected: "-bar,foo",
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			assert.Equal(t, tc.expected, tc.input.String())
+			v := FlagValue{}
+			assert.NoError(t, v.Set(tc.expected))
+			assert.Equal(t, tc.input, v)
+		})
+	}
+}
+
+func TestFlagValue_SetSlice(t *testing.T) {
+	for _, tc := range []struct {
+		name     string
+		input    []string
+		expected FlagValue
+	}{
+		{
+			name:     "single item",
+			input:    []string{"foo"},
+			expected: FlagValue{"foo": true},
+		},
+		{
+			name:     "multiple items",
+			input:    []string{"foo", "-bar", "+baz"},
+			expected: FlagValue{"foo": true, "bar": false, "baz": true},
+		},
+		{
+			name:     "repeated items",
+			input:    []string{"foo", "-bar", "-foo"},
+			expected: FlagValue{"foo": true, "bar": false},
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			v := FlagValue{}
+			assert.NoError(t, v.SetSlice(tc.input))
+			assert.Equal(t, tc.expected, v)
+		})
+	}
+}

service/flags.go

@@ -19,6 +19,7 @@ import (
 	"strings"
 
 	"go.opentelemetry.io/collector/config/configtelemetry"
+	"go.opentelemetry.io/collector/service/featuregate"
 )
 
 var (
@@ -52,6 +53,7 @@ func (s *stringArrayValue) String() string {
 func flags() *flag.FlagSet {
 	flagSet := new(flag.FlagSet)
 	configtelemetry.Flags(flagSet)
+	featuregate.Flags(flagSet)
 
 	// At least until we can use a generic, i.e.: OpenCensus, metrics exporter
 	// we default to Prometheus at port 8888, if not otherwise specified.