feat: export BaseMetrics for forward-compatible custom implementations (#2)

* feat: export BaseMetrics for forward-compatible custom implementations

Replace unexported noopMetrics with exported BaseMetrics. Custom
Metrics implementations embed BaseMetrics so that new methods added
to the interface get safe no-op defaults. Remove redundant NoopMetrics
var — use &BaseMetrics{} directly.

* fix: use BaseMetrics{} value type to avoid allocation, guard nil WithMetrics

Author: ankurs

README.md

@@ -192,6 +192,14 @@ shutdown complete
 - [func EveryInterval\(d time.Duration, fn func\(WorkerContext\) error\) func\(WorkerContext\) error](<#EveryInterval>)
 - [func Run\(ctx context.Context, workers \[\]\*Worker, opts ...RunOption\) error](<#Run>)
 - [func RunWorker\(ctx context.Context, w \*Worker, opts ...RunOption\)](<#RunWorker>)
+- [type BaseMetrics](<#BaseMetrics>)
+  - [func \(BaseMetrics\) ObserveRunDuration\(string, time.Duration\)](<#BaseMetrics.ObserveRunDuration>)
+  - [func \(BaseMetrics\) SetActiveWorkers\(int\)](<#BaseMetrics.SetActiveWorkers>)
+  - [func \(BaseMetrics\) WorkerFailed\(string, error\)](<#BaseMetrics.WorkerFailed>)
+  - [func \(BaseMetrics\) WorkerPanicked\(string\)](<#BaseMetrics.WorkerPanicked>)
+  - [func \(BaseMetrics\) WorkerRestarted\(string, int\)](<#BaseMetrics.WorkerRestarted>)
+  - [func \(BaseMetrics\) WorkerStarted\(string\)](<#BaseMetrics.WorkerStarted>)
+  - [func \(BaseMetrics\) WorkerStopped\(string\)](<#BaseMetrics.WorkerStopped>)
 - [type Metrics](<#Metrics>)
   - [func NewPrometheusMetrics\(namespace string\) Metrics](<#NewPrometheusMetrics>)
 - [type RunOption](<#RunOption>)
@@ -210,7 +218,7 @@ shutdown complete
 
 
 <a name="BatchChannelWorker"></a>
-## func BatchChannelWorker
+## func [BatchChannelWorker](<https://github.com/go-coldbrew/workers/blob/main/helpers.go#L49>)
 
 ```go
 func BatchChannelWorker[T any](ch <-chan T, maxSize int, maxDelay time.Duration, fn func(WorkerContext, []T) error) func(WorkerContext) error
@@ -265,7 +273,7 @@ func main() {
 </details>
 
 <a name="ChannelWorker"></a>
-## func ChannelWorker
+## func [ChannelWorker](<https://github.com/go-coldbrew/workers/blob/main/helpers.go#L27>)
 
 ```go
 func ChannelWorker[T any](ch <-chan T, fn func(WorkerContext, T) error) func(WorkerContext) error
@@ -321,7 +329,7 @@ world
 </details>
 
 <a name="EveryInterval"></a>
-## func EveryInterval
+## func [EveryInterval](<https://github.com/go-coldbrew/workers/blob/main/helpers.go#L8>)
 
 ```go
 func EveryInterval(d time.Duration, fn func(WorkerContext) error) func(WorkerContext) error
@@ -373,7 +381,7 @@ tick 2
 </details>
 
 <a name="Run"></a>
-## func Run
+## func [Run](<https://github.com/go-coldbrew/workers/blob/main/run.go#L120>)
 
 ```go
 func Run(ctx context.Context, workers []*Worker, opts ...RunOption) error
@@ -429,7 +437,7 @@ all workers stopped
 </details>
 
 <a name="RunWorker"></a>
-## func RunWorker
+## func [RunWorker](<https://github.com/go-coldbrew/workers/blob/main/run.go#L143>)
 
 ```go
 func RunWorker(ctx context.Context, w *Worker, opts ...RunOption)
@@ -478,10 +486,93 @@ done
 </p>
 </details>
 
+<a name="BaseMetrics"></a>
+## type [BaseMetrics](<https://github.com/go-coldbrew/workers/blob/main/metrics.go#L43>)
+
+BaseMetrics provides no\-op implementations of all Metrics methods. Embed it in custom Metrics implementations so that new methods added to the Metrics interface in future versions get safe no\-op defaults instead of breaking your build:
+
+```
+type myMetrics struct {
+    workers.BaseMetrics // forward-compatible
+    client *statsd.Client
+}
+
+func (m *myMetrics) WorkerStarted(name string) {
+    m.client.Incr("worker.started", []string{"worker:" + name}, 1)
+}
+```
+
+```go
+type BaseMetrics struct{}
+```
+
+<a name="BaseMetrics.ObserveRunDuration"></a>
+### func \(BaseMetrics\) [ObserveRunDuration](<https://github.com/go-coldbrew/workers/blob/main/metrics.go#L50>)
+
+```go
+func (BaseMetrics) ObserveRunDuration(string, time.Duration)
+```
+
+
+
+<a name="BaseMetrics.SetActiveWorkers"></a>
+### func \(BaseMetrics\) [SetActiveWorkers](<https://github.com/go-coldbrew/workers/blob/main/metrics.go#L51>)
+
+```go
+func (BaseMetrics) SetActiveWorkers(int)
+```
+
+
+
+<a name="BaseMetrics.WorkerFailed"></a>
+### func \(BaseMetrics\) [WorkerFailed](<https://github.com/go-coldbrew/workers/blob/main/metrics.go#L48>)
+
+```go
+func (BaseMetrics) WorkerFailed(string, error)
+```
+
+
+
+<a name="BaseMetrics.WorkerPanicked"></a>
+### func \(BaseMetrics\) [WorkerPanicked](<https://github.com/go-coldbrew/workers/blob/main/metrics.go#L47>)
+
+```go
+func (BaseMetrics) WorkerPanicked(string)
+```
+
+
+
+<a name="BaseMetrics.WorkerRestarted"></a>
+### func \(BaseMetrics\) [WorkerRestarted](<https://github.com/go-coldbrew/workers/blob/main/metrics.go#L49>)
+
+```go
+func (BaseMetrics) WorkerRestarted(string, int)
+```
+
+
+
+<a name="BaseMetrics.WorkerStarted"></a>
+### func \(BaseMetrics\) [WorkerStarted](<https://github.com/go-coldbrew/workers/blob/main/metrics.go#L45>)
+
+```go
+func (BaseMetrics) WorkerStarted(string)
+```
+
+
+
+<a name="BaseMetrics.WorkerStopped"></a>
+### func \(BaseMetrics\) [WorkerStopped](<https://github.com/go-coldbrew/workers/blob/main/metrics.go#L46>)
+
+```go
+func (BaseMetrics) WorkerStopped(string)
+```
+
+
+
 <a name="Metrics"></a>
-## type Metrics
+## type [Metrics](<https://github.com/go-coldbrew/workers/blob/main/metrics.go#L20-L28>)
 
-Metrics collects worker lifecycle metrics. Implement this interface to provide custom metrics \(e.g., Datadog, StatsD\). Use NoopMetrics to disable metrics, or NewPrometheusMetrics for the built\-in Prometheus implementation.
+Metrics collects worker lifecycle metrics. Implement this interface to provide custom metrics \(e.g., Datadog, StatsD\). Use BaseMetrics\{\} to disable metrics, or NewPrometheusMetrics for the built\-in Prometheus implementation.
 
 ```go
 type Metrics interface {
@@ -495,14 +586,8 @@ type Metrics interface {
 }
 ```
 
-<a name="NoopMetrics"></a>NoopMetrics is a no\-op implementation of Metrics. Used as the default when no metrics are configured via WithMetrics.
-
-```go
-var NoopMetrics Metrics = &noopMetrics{}
-```
-
 <a name="NewPrometheusMetrics"></a>
-### func NewPrometheusMetrics
+### func [NewPrometheusMetrics](<https://github.com/go-coldbrew/workers/blob/main/metrics.go#L71>)
 
 ```go
 func NewPrometheusMetrics(namespace string) Metrics
@@ -511,7 +596,7 @@ func NewPrometheusMetrics(namespace string) Metrics
 NewPrometheusMetrics creates a Metrics implementation backed by Prometheus. The namespace is prepended to all metric names \(e.g., "myapp" → "myapp\_worker\_started\_total"\). Metrics are auto\-registered with the default Prometheus registry. Safe to call multiple times with the same namespace — returns the cached instance. The cache is process\-global; use a small number of static namespaces \(not per\-request/tenant values\).
 
 <a name="RunOption"></a>
-## type RunOption
+## type [RunOption](<https://github.com/go-coldbrew/workers/blob/main/run.go#L15>)
 
 RunOption configures the behavior of Run.
 
@@ -520,16 +605,16 @@ type RunOption func(*runConfig)
 ```
 
 <a name="WithMetrics"></a>
-### func WithMetrics
+### func [WithMetrics](<https://github.com/go-coldbrew/workers/blob/main/run.go#L24>)
 
 ```go
 func WithMetrics(m Metrics) RunOption
 ```
 
-WithMetrics sets the metrics implementation for all workers started by Run. Workers inherit this unless they override via Worker.WithMetrics. If not set, NoopMetrics is used.
+WithMetrics sets the metrics implementation for all workers started by Run. Workers inherit this unless they override via Worker.WithMetrics. If not set, BaseMetrics\{\} is used.
 
 <a name="Worker"></a>
-## type Worker
+## type [Worker](<https://github.com/go-coldbrew/workers/blob/main/worker.go#L127-L137>)
 
 Worker represents a background goroutine managed by the framework. Create with NewWorker and configure with builder methods.
 
@@ -540,7 +625,7 @@ type Worker struct {
 ```
 
 <a name="NewWorker"></a>
-### func NewWorker
+### func [NewWorker](<https://github.com/go-coldbrew/workers/blob/main/worker.go#L141>)
 
 ```go
 func NewWorker(name string, run func(WorkerContext) error) *Worker
@@ -588,7 +673,7 @@ worker "greeter" started (attempt 0)
 </details>
 
 <a name="Worker.Every"></a>
-### func \(\*Worker\) Every
+### func \(\*Worker\) [Every](<https://github.com/go-coldbrew/workers/blob/main/worker.go#L198>)
 
 ```go
 func (w *Worker) Every(d time.Duration) *Worker
@@ -638,7 +723,7 @@ tick 2
 </details>
 
 <a name="Worker.WithBackoffJitter"></a>
-### func \(\*Worker\) WithBackoffJitter
+### func \(\*Worker\) [WithBackoffJitter](<https://github.com/go-coldbrew/workers/blob/main/worker.go#L175>)
 
 ```go
 func (w *Worker) WithBackoffJitter(jitter suture.Jitter) *Worker
@@ -647,7 +732,7 @@ func (w *Worker) WithBackoffJitter(jitter suture.Jitter) *Worker
 WithBackoffJitter adds random jitter to the backoff duration to prevent thundering herd on coordinated restarts.
 
 <a name="Worker.WithFailureBackoff"></a>
-### func \(\*Worker\) WithFailureBackoff
+### func \(\*Worker\) [WithFailureBackoff](<https://github.com/go-coldbrew/workers/blob/main/worker.go#L168>)
 
 ```go
 func (w *Worker) WithFailureBackoff(d time.Duration) *Worker
@@ -656,7 +741,7 @@ func (w *Worker) WithFailureBackoff(d time.Duration) *Worker
 WithFailureBackoff sets the duration to wait between restarts. Suture default is 15 seconds.
 
 <a name="Worker.WithFailureDecay"></a>
-### func \(\*Worker\) WithFailureDecay
+### func \(\*Worker\) [WithFailureDecay](<https://github.com/go-coldbrew/workers/blob/main/worker.go#L154>)
 
 ```go
 func (w *Worker) WithFailureDecay(decay float64) *Worker
@@ -665,7 +750,7 @@ func (w *Worker) WithFailureDecay(decay float64) *Worker
 WithFailureDecay sets the rate at which failure count decays over time. A value of 1.0 means failures decay by one per second. Suture default is 1.0.
 
 <a name="Worker.WithFailureThreshold"></a>
-### func \(\*Worker\) WithFailureThreshold
+### func \(\*Worker\) [WithFailureThreshold](<https://github.com/go-coldbrew/workers/blob/main/worker.go#L161>)
 
 ```go
 func (w *Worker) WithFailureThreshold(threshold float64) *Worker
@@ -674,7 +759,7 @@ func (w *Worker) WithFailureThreshold(threshold float64) *Worker
 WithFailureThreshold sets the number of failures allowed before the supervisor gives up restarting. Suture default is 5.
 
 <a name="Worker.WithMetrics"></a>
-### func \(\*Worker\) WithMetrics
+### func \(\*Worker\) [WithMetrics](<https://github.com/go-coldbrew/workers/blob/main/worker.go#L189>)
 
 ```go
 func (w *Worker) WithMetrics(m Metrics) *Worker
@@ -683,7 +768,7 @@ func (w *Worker) WithMetrics(m Metrics) *Worker
 WithMetrics sets a per\-worker metrics implementation, overriding the metrics inherited from the parent WorkerContext or Run options.
 
 <a name="Worker.WithRestart"></a>
-### func \(\*Worker\) WithRestart
+### func \(\*Worker\) [WithRestart](<https://github.com/go-coldbrew/workers/blob/main/worker.go#L147>)
 
 ```go
 func (w *Worker) WithRestart(restart bool) *Worker
@@ -732,7 +817,7 @@ func main() {
 </details>
 
 <a name="Worker.WithTimeout"></a>
-### func \(\*Worker\) WithTimeout
+### func \(\*Worker\) [WithTimeout](<https://github.com/go-coldbrew/workers/blob/main/worker.go#L182>)
 
 ```go
 func (w *Worker) WithTimeout(d time.Duration) *Worker
@@ -741,7 +826,7 @@ func (w *Worker) WithTimeout(d time.Duration) *Worker
 WithTimeout sets the maximum time to wait for the worker to stop during graceful shutdown. Suture default is 10 seconds.
 
 <a name="WorkerContext"></a>
-## type WorkerContext
+## type [WorkerContext](<https://github.com/go-coldbrew/workers/blob/main/worker.go#L52-L66>)
 
 WorkerContext extends context.Context with worker metadata and dynamic child worker management. The framework creates these — users never need to implement this interface.
 

metrics.go

@@ -15,7 +15,7 @@ var (
 
 // Metrics collects worker lifecycle metrics.
 // Implement this interface to provide custom metrics (e.g., Datadog, StatsD).
-// Use NoopMetrics to disable metrics, or NewPrometheusMetrics for the built-in
+// Use BaseMetrics{} to disable metrics, or NewPrometheusMetrics for the built-in
 // Prometheus implementation.
 type Metrics interface {
 	WorkerStarted(name string)
@@ -27,19 +27,28 @@ type Metrics interface {
 	SetActiveWorkers(count int)
 }
 
-// NoopMetrics is a no-op implementation of Metrics. Used as the default
-// when no metrics are configured via WithMetrics.
-var NoopMetrics Metrics = &noopMetrics{}
-
-type noopMetrics struct{}
-
-func (n *noopMetrics) WorkerStarted(string)                  {}
-func (n *noopMetrics) WorkerStopped(string)                  {}
-func (n *noopMetrics) WorkerPanicked(string)                 {}
-func (n *noopMetrics) WorkerFailed(string, error)            {}
-func (n *noopMetrics) WorkerRestarted(string, int)           {}
-func (n *noopMetrics) ObserveRunDuration(string, time.Duration) {}
-func (n *noopMetrics) SetActiveWorkers(int)                  {}
+// BaseMetrics provides no-op implementations of all Metrics methods.
+// Embed it in custom Metrics implementations so that new methods added
+// to the Metrics interface in future versions get safe no-op defaults
+// instead of breaking your build:
+//
+//	type myMetrics struct {
+//	    workers.BaseMetrics // forward-compatible
+//	    client *statsd.Client
+//	}
+//
+//	func (m *myMetrics) WorkerStarted(name string) {
+//	    m.client.Incr("worker.started", []string{"worker:" + name}, 1)
+//	}
+type BaseMetrics struct{}
+
+func (BaseMetrics) WorkerStarted(string)                     {}
+func (BaseMetrics) WorkerStopped(string)                     {}
+func (BaseMetrics) WorkerPanicked(string)                    {}
+func (BaseMetrics) WorkerFailed(string, error)               {}
+func (BaseMetrics) WorkerRestarted(string, int)              {}
+func (BaseMetrics) ObserveRunDuration(string, time.Duration) {}
+func (BaseMetrics) SetActiveWorkers(int)                     {}
 
 // prometheusMetrics implements Metrics using Prometheus counters, histograms,
 // and gauges registered via promauto.

run.go

@@ -20,10 +20,12 @@ type runConfig struct {
 
 // WithMetrics sets the metrics implementation for all workers started by Run.
 // Workers inherit this unless they override via Worker.WithMetrics.
-// If not set, NoopMetrics is used.
+// If not set, BaseMetrics{} is used.
 func WithMetrics(m Metrics) RunOption {
 	return func(c *runConfig) {
-		c.metrics = m
+		if m != nil {
+			c.metrics = m
+		}
 	}
 }
 
@@ -97,7 +99,7 @@ func resolveMetrics(w *Worker, parent Metrics) Metrics {
 	if parent != nil {
 		return parent
 	}
-	return NoopMetrics
+	return BaseMetrics{}
 }
 
 // addWorkerToSupervisor creates a child supervisor for the worker,
@@ -116,7 +118,7 @@ func addWorkerToSupervisor(parent *suture.Supervisor, w *Worker, metrics Metrics
 // A worker exiting early (without restart) does not stop other workers.
 // Returns nil on clean shutdown.
 func Run(ctx context.Context, workers []*Worker, opts ...RunOption) error {
-	cfg := &runConfig{metrics: NoopMetrics}
+	cfg := &runConfig{metrics: BaseMetrics{}}
 	for _, opt := range opts {
 		opt(cfg)
 	}

worker.go

@@ -117,7 +117,7 @@ func (wc *workerContext) Children() []string {
 
 func newWorkerContext(ctx context.Context, name string, attempt int, sup *suture.Supervisor, metrics Metrics, active *atomic.Int32) WorkerContext {
 	if metrics == nil {
-		metrics = NoopMetrics
+		metrics = BaseMetrics{}
 	}
 	return &workerContext{Context: ctx, name: name, attempt: attempt, sup: sup, metrics: metrics, active: active}
 }