Added metrics to SFlux/SMono

src/main/scala/reactor/core/scala/publisher/SFlux.scala

@@ -570,6 +570,17 @@ trait SFlux[T] extends SFluxLike[T, SFlux] with MapablePublisher[T] with ScalaCo
 
   final def mergeWith(other: Publisher[_ <: T]): SFlux[T] = SFlux.fromPublisher(coreFlux.mergeWith(other))
 
+  /**
+  * Activate metrics for this sequence, provided there is an instrumentation facade
+  * on the classpath (otherwise this method is a pure no-op).
+  * <p>
+  * Metrics are gathered on [[Subscriber]] events, and it is recommended to also
+  * [[name]] (and optionally [[tag]]) the sequence.
+  *
+  * @return an instrumented [[SFlux]]
+  */
+  final def metrics: SFlux[T] = SFlux.fromPublisher(coreFlux.metrics())
+
   final def name(name: String): SFlux[T] = SFlux.fromPublisher(coreFlux.name(name))
 
   final def next(): SMono[T] = SMono.fromPublisher(coreFlux.next())

src/main/scala/reactor/core/scala/publisher/SMono.scala

@@ -738,8 +738,19 @@ trait SMono[T] extends SMonoLike[T, SMono] with MapablePublisher[T] with ScalaCo
   final def mergeWith(other: Publisher[_ <: T]): SFlux[T] = coreMono.mergeWith(other).asScala
 
   /**
-    * Give a name to this sequence, which can be retrieved using [[Scannable.name()]]
-    * as long as this is the first reachable [[Scannable.parents()]].
+    * Activate metrics for this sequence, provided there is an instrumentation facade
+    * on the classpath (otherwise this method is a pure no-op).
+    * <p>
+    * Metrics are gathered on [[Subscriber]] events, and it is recommended to also
+    * [[name]] (and optionally [[tag]]) the sequence.
+    *
+    * @return an instrumented [[SMono]]
+    */
+  final def metrics: SMono[T] = SMono.fromPublisher(coreMono.metrics())
+
+  /**
+    * Give a name to this sequence, which can be retrieved using [[Scannable.name]]
+    * as long as this is the first reachable [[Scannable.parents]].
     *
     * @param name a name for the sequence
     * @return the same sequence, but bearing a name

src/test/scala/reactor/core/scala/publisher/SFluxTest.scala

@@ -1526,6 +1526,11 @@ class SFluxTest extends AnyFreeSpec with Matchers with TableDrivenPropertyChecks
         .expectNext(1, 2, 3, 4, 5, 6)
         .verifyComplete()
     }
+
+    ".metrics should be a nop since Micrometer is not on the classpath" in {
+      val flux = JFlux.just("plain", "awesome")
+      flux.asScala.metrics.coreFlux shouldBe theSameInstanceAs(flux)
+    }
 
     ".min" - {
       "of numbers should emit the lowest value of ordering" in {

src/test/scala/reactor/core/scala/publisher/SMonoTest.scala

@@ -163,6 +163,11 @@ class SMonoTest extends AnyFreeSpec with Matchers with TestSupport with Idiomati
         }
       }
     }
+
+    ".metrics should be a nop since Micrometer is not on the classpath" in {
+      val mono = JMono.just("plain awesome")
+      mono.asScala.metrics.coreMono shouldBe theSameInstanceAs(mono)
+    }
 
     ".never will never signal any data, error or completion signal" in {
       StepVerifier.create(SMono.never)