feat(mdatagen): add automatic feature gate documentation generation

cmd/mdatagen/README.md

@@ -1,23 +1,25 @@
 # Metadata Generator
 
 <!-- status autogenerated section -->
-| Status        |           |
-| ------------- |-----------|
-| Stability     | [alpha]: metrics   |
-| Issues        | [![Open issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector?query=is%3Aissue%20is%3Aopen%20label%3Acmd%2Fmdatagen%20&label=open&color=orange&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector/issues?q=is%3Aopen+is%3Aissue+label%3Acmd%2Fmdatagen) [![Closed issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector?query=is%3Aissue%20is%3Aclosed%20label%3Acmd%2Fmdatagen%20&label=closed&color=blue&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector/issues?q=is%3Aclosed+is%3Aissue+label%3Acmd%2Fmdatagen) |
-| [Code Owners](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/CONTRIBUTING.md#becoming-a-code-owner)    | [@dmitryax](https://www.github.com/dmitryax) |
+
+| Status                                                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
+| -------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| Stability                                                                                                                        | [alpha]: metrics                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
+| Issues                                                                                                                           | [![Open issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector?query=is%3Aissue%20is%3Aopen%20label%3Acmd%2Fmdatagen%20&label=open&color=orange&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector/issues?q=is%3Aopen+is%3Aissue+label%3Acmd%2Fmdatagen) [![Closed issues](https://img.shields.io/github/issues-search/open-telemetry/opentelemetry-collector?query=is%3Aissue%20is%3Aclosed%20label%3Acmd%2Fmdatagen%20&label=closed&color=blue&logo=opentelemetry)](https://github.com/open-telemetry/opentelemetry-collector/issues?q=is%3Aclosed+is%3Aissue+label%3Acmd%2Fmdatagen) |
+| [Code Owners](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/CONTRIBUTING.md#becoming-a-code-owner) | [@dmitryax](https://www.github.com/dmitryax)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
 
 [alpha]: https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/component-stability.md#alpha
+
 <!-- end autogenerated section -->
 
 Every component's documentation should include a brief description of the component and guidance on how to use it.
 There is also some information about the component (or metadata) that should be included to help end-users understand the current state of the component and whether it is right for their use case.
 Examples of this metadata about a component are:
 
-* its stability level
-* the distributions containing it
-* the types of pipelines it supports
-* metrics emitted in the case of a scraping receiver, a scraper, or a connector
+- its stability level
+- the distributions containing it
+- the types of pipelines it supports
+- metrics emitted in the case of a scraping receiver, a scraper, or a connector
 
 The metadata generator defines a schema for specifying this information to ensure it is complete and well-formed.
 The metadata generator is then able to ingest the metadata, validate it against the schema and produce documentation in a standardized format.
@@ -26,10 +28,12 @@
 ## Using the Metadata Generator
 
 In order for a component to benefit from the metadata generator (`mdatagen`) these requirements need to be met:
+
 1. A yaml file containing the metadata that needs to be included in the component
 2. The component should declare a `go:generate mdatagen` directive which tells `mdatagen` what to generate
 
 As an example, here is a minimal `metadata.yaml` for the [OTLP receiver](https://github.com/open-telemetry/opentelemetry-collector/tree/main/receiver/otlpreceiver):
+
 ```yaml
 type: otlp
 status:
@@ -42,6 +46,7 @@
 Detailed information about the schema of `metadata.yaml` can be found in [metadata-schema.yaml](./metadata-schema.yaml).
 
 The `go:generate mdatagen` directive is usually defined in a `doc.go` file in the same package as the component, for example:
+
 ```go
 //go:generate mdatagen metadata.yaml
 
@@ -50,11 +55,48 @@
 
 Below are some more examples that can be used for reference:
 
-* The ElasticSearch receiver has an extensive [metadata.yaml](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/receiver/elasticsearchreceiver/metadata.yaml)
-* The host metrics receiver has internal subcomponents, each with their own `metadata.yaml` and `doc.go`. See [cpuscraper](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/receiver/hostmetricsreceiver/internal/scraper/cpuscraper) for example.
+- The ElasticSearch receiver has an extensive [metadata.yaml](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/receiver/elasticsearchreceiver/metadata.yaml)
+- The host metrics receiver has internal subcomponents, each with their own `metadata.yaml` and `doc.go`. See [cpuscraper](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/receiver/hostmetricsreceiver/internal/scraper/cpuscraper) for example.
 
 You can run `cd cmd/mdatagen && $(GOCMD) install .` to install the `mdatagen` tool in `GOBIN` and then run `mdatagen metadata.yaml` to generate documentation for a specific component or you can run `make generate` to generate documentation for all components.
 
+### Feature Gates Documentation
+
+The metadata generator supports automatic documentation generation for feature gates used by components. Feature gates are documented by adding a `feature_gates` section to your `metadata.yaml`:
+
+```yaml
+type: mycomponent
+status:
+  class: receiver
+  stability:
+    beta: [metrics, traces]
+
+feature_gates:
+  - id: mycomponent.newFeature
+    description: 'Enables new feature functionality that improves performance'
+    stage: alpha
+    from_version: 'v0.100.0'
+    reference_url: 'https://github.com/open-telemetry/opentelemetry-collector/issues/12345'
+
+  - id: mycomponent.stableFeature
+    description: 'A feature that has reached stability'
+    stage: stable
+    from_version: 'v0.90.0'
+    to_version: 'v0.95.0'
+    reference_url: 'https://github.com/open-telemetry/opentelemetry-collector/issues/11111'
+```
+
+This will generate a "Feature Gates" section in the component's `documentation.md` file with a table containing:
+
+- **Feature Gate**: The gate identifier
+- **Stage**: The lifecycle stage (alpha, beta, stable, deprecated)
+- **Description**: Brief description of what the gate controls
+- **From Version**: Version when the gate was introduced
+- **To Version**: Version when stable/deprecated gates will be removed (if applicable)
+- **Reference**: Link to additional contextual information
+
+The feature gate definitions should correspond to actual gates registered in your component code using the [Feature Gates API](../../featuregate/README.md).
+
 ### Generate multiple metadata packages
 
 By default, `mdatagen` will generate a package called `metadata` in the `internal` directory. If you want to generate a package with a different name, you can use the `generated_package_name` configuration field to provide an alternate name.

cmd/mdatagen/internal/command.go

@@ -172,7 +172,7 @@ func run(ymlPath string) error {
 		}
 	}
 
-	if len(md.Metrics) != 0 || len(md.Telemetry.Metrics) != 0 || len(md.ResourceAttributes) != 0 || len(md.Events) != 0 { // if there's metrics or internal metrics or events, generate documentation for them
+	if len(md.Metrics) != 0 || len(md.Telemetry.Metrics) != 0 || len(md.ResourceAttributes) != 0 || len(md.Events) != 0 || len(md.FeatureGates) != 0 { // if there's metrics or internal metrics or events or feature gates, generate documentation for them
 		toGenerate[filepath.Join(tmplDir, "documentation.md.tmpl")] = filepath.Join(ymlDir, "documentation.md")
 	}
 

cmd/mdatagen/internal/command_test.go

@@ -47,6 +47,7 @@ func TestRunContents(t *testing.T) {
 		wantGoleakSkip                  bool
 		wantGoleakSetup                 bool
 		wantGoleakTeardown              bool
+		wantDocumentationGenerated      bool
 		wantErr                         bool
 		wantOrderErr                    bool
 		wantAttributes                  []string
@@ -192,6 +193,13 @@ func TestRunContents(t *testing.T) {
 			wantComponentTestGenerated: true,
 			wantLogsGenerated:          true,
 		},
+		{
+			yml:                        "feature_gates.yaml",
+			wantStatusGenerated:        true,
+			wantReadmeGenerated:        true,
+			wantComponentTestGenerated: true,
+			wantDocumentationGenerated: true,
+		},
 		{
 			yml:                        "with_conditional_attribute.yaml",
 			wantStatusGenerated:        true,
@@ -301,7 +309,9 @@ foo
 				require.NoFileExists(t, filepath.Join(tmpdir, generatedPackageDir, "generated_telemetry.go"))
 			}
 
-			if !tt.wantMetricsGenerated && !tt.wantTelemetryGenerated && !tt.wantResourceAttributesGenerated && !tt.wantEventsGenerated {
+			if tt.wantDocumentationGenerated {
+				require.FileExists(t, filepath.Join(tmpdir, "documentation.md"))
+			} else if !tt.wantMetricsGenerated && !tt.wantTelemetryGenerated && !tt.wantResourceAttributesGenerated && !tt.wantEventsGenerated {
 				require.NoFileExists(t, filepath.Join(tmpdir, "documentation.md"))
 			}
 

cmd/mdatagen/internal/embedded_templates_test.go

@@ -40,6 +40,7 @@ func TestEnsureTemplatesLoaded(t *testing.T) {
 			path.Join(rootDir, "telemetrytest.go.tmpl"):        {},
 			path.Join(rootDir, "telemetrytest_test.go.tmpl"):   {},
 			path.Join(rootDir, "helper.tmpl"):                  {},
+			path.Join(rootDir, "feature_gates.md.tmpl"):        {},
 		}
 		count = 0
 	)

cmd/mdatagen/internal/metadata.go

@@ -48,6 +48,9 @@ type Metadata struct {
 	Tests Tests `mapstructure:"tests"`
 	// PackageName is the name of the package where the component is defined.
 	PackageName string `mapstructure:"package_name"`
+	// FeatureGates that are managed by the component.
+	FeatureGates []FeatureGate `mapstructure:"feature_gates"`
+	// FeatureGates that are managed by the component.
 }
 
 func (md Metadata) GetCodeCovComponentID() string {
@@ -89,6 +92,10 @@ func (md *Metadata) Validate() error {
 		errs = errors.Join(errs, err)
 	}
 
+	if err := md.validateFeatureGates(); err != nil {
+		errs = errors.Join(errs, err)
+	}
+
 	return errs
 }
 
@@ -270,6 +277,74 @@ func validateEvents(events map[EventName]Event, attributes map[AttributeName]Att
 	return errs
 }
 
+func (md *Metadata) validateFeatureGates() error {
+	var errs error
+	seen := make(map[FeatureGateID]bool)
+	idRegexp := regexp.MustCompile(`^[0-9a-zA-Z.]*$`)
+
+	// Validate that feature gates are sorted by ID
+	if !slices.IsSortedFunc(md.FeatureGates, func(a, b FeatureGate) int {
+		return strings.Compare(string(a.ID), string(b.ID))
+	}) {
+		errs = errors.Join(errs, errors.New("feature gates must be sorted by ID"))
+	}
+
+	for i, gate := range md.FeatureGates {
+		// Validate gate ID is not empty
+		if string(gate.ID) == "" {
+			errs = errors.Join(errs, fmt.Errorf("feature gate at index %d: ID cannot be empty", i))
+			continue
+		}
+
+		// Validate ID follows the allowed character pattern
+		if !idRegexp.MatchString(string(gate.ID)) {
+			errs = errors.Join(errs, fmt.Errorf(`feature gate "%v": ID contains invalid characters, must match ^[0-9a-zA-Z.]*$`, gate.ID))
+		}
+
+		// Check for duplicate IDs
+		if seen[gate.ID] {
+			errs = errors.Join(errs, fmt.Errorf(`feature gate "%v": duplicate ID`, gate.ID))
+			continue
+		}
+		seen[gate.ID] = true
+
+		// Validate gate has required fields
+		if gate.Description == "" {
+			errs = errors.Join(errs, fmt.Errorf(`feature gate "%v": description is required`, gate.ID))
+		}
+
+		// Validate that each feature gate has a reference link
+		if gate.ReferenceURL == "" {
+			errs = errors.Join(errs, fmt.Errorf(`feature gate "%v": reference_url is required`, gate.ID))
+		}
+
+		// Validate stage is one of the allowed values
+		validStages := map[FeatureGateStage]bool{
+			FeatureGateStageAlpha:      true,
+			FeatureGateStageBeta:       true,
+			FeatureGateStageStable:     true,
+			FeatureGateStageDeprecated: true,
+		}
+		if !validStages[gate.Stage] {
+			errs = errors.Join(errs, fmt.Errorf(`feature gate "%v": invalid stage "%v", must be one of: alpha, beta, stable, deprecated`, gate.ID, gate.Stage))
+		}
+
+		// Validate version formats if provided
+		if gate.FromVersion != "" && !strings.HasPrefix(gate.FromVersion, "v") {
+			errs = errors.Join(errs, fmt.Errorf(`feature gate "%v": from_version "%v" must start with 'v'`, gate.ID, gate.FromVersion))
+		}
+		if gate.ToVersion != "" && !strings.HasPrefix(gate.ToVersion, "v") {
+			errs = errors.Join(errs, fmt.Errorf(`feature gate "%v": to_version "%v" must start with 'v'`, gate.ID, gate.ToVersion))
+		}
+
+		// Validate that stable/deprecated gates should have to_version
+		if (gate.Stage == FeatureGateStageStable || gate.Stage == FeatureGateStageDeprecated) && gate.ToVersion == "" {
+			errs = errors.Join(errs, fmt.Errorf(`feature gate "%v": to_version is required for %v stage gates`, gate.ID, gate.Stage))
+		}
+	}
+	return errs
+}
+
 type AttributeName string
 
 // AttributeRequirementLevel defines the requirement level of an attribute.
@@ -514,3 +589,32 @@ type EntityAttributeRef struct {
 	// Ref is the reference to a resource attribute.
 	Ref AttributeName `mapstructure:"ref"`
 }
+
+// FeatureGateID represents the identifier for a feature gate.
+type FeatureGateID string
+
+// FeatureGateStage represents the lifecycle stage of a feature gate.
+type FeatureGateStage string
+
+const (
+	FeatureGateStageAlpha      FeatureGateStage = "alpha"
+	FeatureGateStageBeta       FeatureGateStage = "beta"
+	FeatureGateStageStable     FeatureGateStage = "stable"
+	FeatureGateStageDeprecated FeatureGateStage = "deprecated"
+)
+
+// FeatureGate represents a feature gate definition in metadata.
+type FeatureGate struct {
+	// ID is the unique identifier for the feature gate.
+	ID FeatureGateID `mapstructure:"id"`
+	// Description of the feature gate.
+	Description string `mapstructure:"description"`
+	// Stage is the lifecycle stage of the feature gate.
+	Stage FeatureGateStage `mapstructure:"stage"`
+	// FromVersion is the version when the feature gate was introduced.
+	FromVersion string `mapstructure:"from_version"`
+	// ToVersion is the version when the feature gate reached stable stage.
+	ToVersion string `mapstructure:"to_version"`
+	// ReferenceURL is the URL with contextual information about the feature gate.
+	ReferenceURL string `mapstructure:"reference_url"`
+}