Add a collector flag to list available components.

Add a `--list-components` flag to the collector service. This currently
show all the available components, their types and their signal stability
levels. In future, we could also show the Go module and version, but
that would require changes to the builder, so it's omitted for now.

This fixes open-telemetry#5709.

Signed-off-by: James Peach <jpeach@cloudflare.com>

CHANGELOG.md

@@ -10,6 +10,7 @@
 - Expose `pcommon.NewSliceFromRaw` function (#5679)
 - `loggingexporter`: create the exporter's logger from the service's logger (#5677)
 - Add `otelcol_exporter_queue_capacity` metrics show the collector's exporter queue capacity (#5475)
+- Add the Collector flag `--list-components` flag to show the available components. (#5709)
 
 ### 🧰 Bug fixes 🧰
 

config/common.go

@@ -50,6 +50,11 @@ const (
 	LogsDataType DataType = "logs"
 )
 
+// AllDataTypes is a slice of all possible DataType values.
+var AllDataTypes = []DataType{
+	TracesDataType, MetricsDataType, LogsDataType,
+}
+
 func unmarshal(componentSection *confmap.Conf, intoCfg interface{}) error {
 	if cu, ok := intoCfg.(Unmarshallable); ok {
 		return cu.Unmarshal(componentSection)

service/command.go

@@ -15,13 +15,57 @@
 package service // import "go.opentelemetry.io/collector/service"
 
 import (
+	"fmt"
+	"os"
+	"strings"
+
 	"github.com/spf13/cobra"
 
+	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/config"
 	"go.opentelemetry.io/collector/confmap"
 	"go.opentelemetry.io/collector/confmap/converter/overwritepropertiesconverter"
 	"go.opentelemetry.io/collector/service/featuregate"
 )
 
+func printComponentSet(set CollectorSettings) {
+	printFactory := func(f component.Factory) {
+		var stability []string
+
+		for _, t := range config.AllDataTypes {
+			if s := f.StabilityLevel(t); s != component.StabilityLevelUndefined {
+				stability = append(stability, fmt.Sprintf("%s: %s", t, s))
+			}
+		}
+
+		if len(stability) == 0 {
+			fmt.Printf("\t%s\n", f.Type())
+		} else {
+			fmt.Printf("\t%s (%s)\n", f.Type(), strings.Join(stability, ", "))
+		}
+	}
+
+	fmt.Printf("exporters:\n")
+	for _, e := range set.Factories.Exporters {
+		printFactory(e)
+	}
+
+	fmt.Printf("receivers:\n")
+	for _, r := range set.Factories.Receivers {
+		printFactory(r)
+	}
+
+	fmt.Printf("processors:\n")
+	for _, p := range set.Factories.Processors {
+		printFactory(p)
+	}
+
+	fmt.Printf("extensions:\n")
+	for _, e := range set.Factories.Extensions {
+		printFactory(e)
+	}
+}
+
 // NewCommand constructs a new cobra.Command using the given CollectorSettings.
 func NewCommand(set CollectorSettings) *cobra.Command {
 	flagSet := flags()
@@ -30,6 +74,10 @@ func NewCommand(set CollectorSettings) *cobra.Command {
 		Version:      set.BuildInfo.Version,
 		SilenceUsage: true,
 		RunE: func(cmd *cobra.Command, args []string) error {
+			if getListComponentsFlag(flagSet) {
+				printComponentSet(set)
+				os.Exit(0)
+			}
 			featuregate.GetRegistry().Apply(gatesList)
 			if set.ConfigProvider == nil {
 				var err error

service/flags.go

@@ -60,6 +60,9 @@ func flags() *flag.FlagSet {
 		"feature-gates",
 		"Comma-delimited list of feature gate identifiers. Prefix with '-' to disable the feature. '+' or no prefix will enable the feature.")
 
+	flagSet.Bool("list-components", false,
+		"List the available components and exit.")
+
 	return flagSet
 }
 
@@ -70,3 +73,7 @@ func getConfigFlag(flagSet *flag.FlagSet) []string {
 func getSetFlag(flagSet *flag.FlagSet) []string {
 	return flagSet.Lookup(setFlag).Value.(*stringArrayValue).values
 }
+
+func getListComponentsFlag(flagSet *flag.FlagSet) bool {
+	return flagSet.Lookup("list-components").Value.String() == "true"
+}