chore: Move component registry so it can be reused (#3297)

* Move component registry to component package so it can be reused outside
of runtime package

* Rename interface

Author: kalleep

internal/component/registry.go

@@ -242,3 +242,87 @@ func AllNames() []string {
 	slices.Sort(keys)
 	return keys
 }
+
+// Registry is a collection of registered components.
+type Registry interface {
+	// Get looks up a component by name. It returns an error if the component does not exist or its usage is restricted,
+	// for example, because of the component's stability level.
+	Get(name string) (Registration, error)
+}
+
+type defaultRegistry struct {
+	minStability featuregate.Stability
+	community    bool
+}
+
+// NewDefaultRegistry creates a new [Registry] which gets
+// components registered to github.com/grafana/alloy/internal/component.
+func NewDefaultRegistry(minStability featuregate.Stability, enableCommunityComps bool) Registry {
+	return defaultRegistry{
+		minStability: minStability,
+		community:    enableCommunityComps,
+	}
+}
+
+// Get retrieves a component using [component.Get]. It returns an error if the component does not exist,
+// or if the component's stability is below the minimum required stability level.
+func (reg defaultRegistry) Get(name string) (Registration, error) {
+	cr, exists := Get(name)
+	if !exists {
+		return Registration{}, fmt.Errorf("cannot find the definition of component name %q", name)
+	}
+
+	if cr.Community {
+		if !reg.community {
+			return Registration{}, fmt.Errorf("the component %q is a community component. Use the --feature.community-components.enabled command-line flag to enable community components", name)
+		}
+		return cr, nil // community components are not affected by feature stability
+	}
+
+	err := featuregate.CheckAllowed(cr.Stability, reg.minStability, fmt.Sprintf("component %q", name))
+	if err != nil {
+		return Registration{}, err
+	}
+	return cr, nil
+}
+
+type registryMap struct {
+	registrations map[string]Registration
+	minStability  featuregate.Stability
+	community     bool
+}
+
+// NewRegistryMap creates a new [Registry] which uses a map to store components.
+// Currently, it is only used in tests.
+func NewRegistryMap(
+	minStability featuregate.Stability,
+	community bool,
+	registrations map[string]Registration,
+) Registry {
+
+	return &registryMap{
+		registrations: registrations,
+		minStability:  minStability,
+		community:     community,
+	}
+}
+
+// Get retrieves a component using [component.Get].
+func (m registryMap) Get(name string) (Registration, error) {
+	reg, ok := m.registrations[name]
+	if !ok {
+		return Registration{}, fmt.Errorf("cannot find the definition of component name %q", name)
+	}
+	if reg.Community {
+		if !m.community {
+			return Registration{}, fmt.Errorf("the component %q is a community component. Use the --feature.community-components.enabled command-line flag to enable community components", name)
+		}
+		return reg, nil // community components are not affected by feature stability
+	}
+
+	err := featuregate.CheckAllowed(reg.Stability, m.minStability, fmt.Sprintf("component %q", name))
+	if err != nil {
+		return Registration{}, err
+	}
+	return reg, nil
+}

internal/runtime/alloy.go

@@ -54,6 +54,7 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"go.uber.org/atomic"
 
+	"github.com/grafana/alloy/internal/component"
 	"github.com/grafana/alloy/internal/featuregate"
 	"github.com/grafana/alloy/internal/runtime/internal/controller"
 	"github.com/grafana/alloy/internal/runtime/internal/importsource"
@@ -147,9 +148,9 @@ func New(o Options) *Runtime {
 type controllerOptions struct {
 	Options
 
-	ComponentRegistry controller.ComponentRegistry // Custom component registry used in tests.
-	ModuleRegistry    *moduleRegistry              // Where to register created modules.
-	IsModule          bool                         // Whether this controller is for a module.
+	ComponentRegistry component.Registry // Custom component registry used in tests.
+	ModuleRegistry    *moduleRegistry    // Where to register created modules.
+	IsModule          bool               // Whether this controller is for a module.
 	// A worker pool to evaluate components asynchronously. A default one will be created if this is nil.
 	WorkerPool worker.Pool
 }

internal/runtime/alloy_services_test.go

@@ -7,7 +7,6 @@ import (
 
 	"github.com/grafana/alloy/internal/component"
 	"github.com/grafana/alloy/internal/featuregate"
-	"github.com/grafana/alloy/internal/runtime/internal/controller"
 	"github.com/grafana/alloy/internal/runtime/internal/testcomponents"
 	"github.com/grafana/alloy/internal/runtime/internal/testservices"
 	"github.com/grafana/alloy/internal/service"
@@ -211,7 +210,7 @@ func TestComponents_Using_Services(t *testing.T) {
 			},
 		}
 
-		registry = controller.NewRegistryMap(
+		registry = component.NewRegistryMap(
 			featuregate.StabilityGenerallyAvailable,
 			true,
 			map[string]component.Registration{
@@ -274,7 +273,7 @@ func TestComponents_Using_Services_In_Modules(t *testing.T) {
 			},
 		}
 
-		registry = controller.NewRegistryMap(
+		registry = component.NewRegistryMap(
 			featuregate.StabilityGenerallyAvailable,
 			true,
 			map[string]component.Registration{

internal/runtime/internal/controller/component_node_manager.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"sync"
 
+	"github.com/grafana/alloy/internal/component"
 	"github.com/grafana/alloy/syntax/ast"
 )
 
@@ -12,15 +13,15 @@ import (
 type ComponentNodeManager struct {
 	globals ComponentGlobals
 	// builtinComponentReg returns information to build and run built-in components.
-	builtinComponentReg ComponentRegistry
+	builtinComponentReg component.Registry
 
 	mut sync.RWMutex
 	// customComponentReg returns information to build and run custom components.
 	customComponentReg *CustomComponentRegistry
 }
 
 // NewComponentNodeManager creates a new ComponentNodeManager without custom component registry.
-func NewComponentNodeManager(globals ComponentGlobals, componentReg ComponentRegistry) *ComponentNodeManager {
+func NewComponentNodeManager(globals ComponentGlobals, componentReg component.Registry) *ComponentNodeManager {
 	return &ComponentNodeManager{
 		globals:             globals,
 		builtinComponentReg: componentReg,

internal/runtime/internal/controller/component_registry.go

@@ -18,6 +18,7 @@ import (
 	"go.opentelemetry.io/otel/codes"
 	"go.opentelemetry.io/otel/trace"
 
+	"github.com/grafana/alloy/internal/component"
 	"github.com/grafana/alloy/internal/component/common/loki"
 	"github.com/grafana/alloy/internal/component/otelcol"
 	"github.com/grafana/alloy/internal/featuregate"
@@ -65,10 +66,10 @@ type LoaderOptions struct {
 	// ComponentGlobals contains data to use when creating components.
 	ComponentGlobals ComponentGlobals
 
-	Services          []service.Service // Services to load into the DAG.
-	Host              service.Host      // Service host (when running services).
-	ComponentRegistry ComponentRegistry // Registry to search for components.
-	WorkerPool        worker.Pool       // Worker pool to use for async tasks.
+	Services          []service.Service  // Services to load into the DAG.
+	Host              service.Host       // Service host (when running services).
+	ComponentRegistry component.Registry // Registry to search for components.
+	WorkerPool        worker.Pool        // Worker pool to use for async tasks.
 }
 
 // NewLoader creates a new Loader. Components built by the Loader will be built
@@ -84,7 +85,7 @@ func NewLoader(opts LoaderOptions) *Loader {
 	parent, id := splitPath(globals.ControllerID)
 
 	if reg == nil {
-		reg = NewDefaultComponentRegistry(opts.ComponentGlobals.MinStability, opts.ComponentGlobals.EnableCommunityComps)
+		reg = component.NewDefaultRegistry(opts.ComponentGlobals.MinStability, opts.ComponentGlobals.EnableCommunityComps)
 	}
 
 	l := &Loader{

internal/runtime/internal/controller/loader.go

@@ -214,7 +214,7 @@ type moduleControllerOptions struct {
 	ID string
 
 	// ComponentRegistry is where controllers can look up components.
-	ComponentRegistry controller.ComponentRegistry
+	ComponentRegistry component.Registry
 
 	// ModuleRegistry is a shared registry of running modules from the same root
 	// controller.