trace: add addLink to Span

core/trace/src/main/scala-2/org/typelevel/otel4s/trace/SpanMacro.scala

@@ -119,6 +119,42 @@ private[otel4s] trait SpanMacro[F[_]] {
   ): F[Unit] =
     macro SpanMacro.addEventWithTimestampColl
 
+  /** Adds a link to the span.
+    *
+    * Links are used to link spans in different traces. Used (for example) in
+    * batching operations, where a single batch handler processes multiple
+    * requests from different traces or the same trace.
+    *
+    * @param spanContext
+    *   the context of the linked span
+    *
+    * @param attributes
+    *   the set of attributes to associated with the link
+    */
+  def addLink(
+      spanContext: SpanContext,
+      attributes: Attribute[_]*
+  ): F[Unit] =
+    macro SpanMacro.addLink
+
+  /** Adds a link to the span.
+    *
+    * Links are used to link spans in different traces. Used (for example) in
+    * batching operations, where a single batch handler processes multiple
+    * requests from different traces or the same trace.
+    *
+    * @param spanContext
+    *   the context of the linked span
+    *
+    * @param attributes
+    *   the set of attributes to associated with the link
+    */
+  def addLink(
+      spanContext: SpanContext,
+      attributes: immutable.Iterable[Attribute[_]]
+  ): F[Unit] =
+    macro SpanMacro.addLinkColl
+
   /** Records information about the `Throwable` to the span.
     *
     * @param exception
@@ -227,6 +263,26 @@ object SpanMacro {
     q"if ($meta.isEnabled) $backend.addEvent($name, $attributes) else $meta.unit"
   }
 
+  def addLink(c: blackbox.Context)(
+      spanContext: c.Expr[SpanContext],
+      attributes: c.Expr[Attribute[_]]*
+  ): c.universe.Tree = {
+    import c.universe._
+    addLinkColl(c)(spanContext, c.Expr(q"_root_.scala.Seq(..$attributes)"))
+  }
+
+  def addLinkColl(c: blackbox.Context)(
+      spanContext: c.Expr[SpanContext],
+      attributes: c.Expr[immutable.Iterable[Attribute[_]]]
+  ): c.universe.Tree = {
+    import c.universe._
+
+    val backend = q"${c.prefix}.backend"
+    val meta = q"$backend.meta"
+
+    q"if ($meta.isEnabled) $backend.addLink($spanContext, $attributes) else $meta.unit"
+  }
+
   def addEventWithTimestamp(c: blackbox.Context)(
       name: c.Expr[String],
       timestamp: c.Expr[FiniteDuration],

core/trace/src/main/scala-3/org/typelevel/otel4s/trace/SpanMacro.scala

@@ -125,6 +125,42 @@ private[otel4s] trait SpanMacro[F[_]] {
   ): F[Unit] =
     ${ SpanMacro.addEvent('self, 'name, 'timestamp, 'attributes) }
 
+  /** Adds a link to the span.
+    *
+    * Links are used to link spans in different traces. Used (for example) in
+    * batching operations, where a single batch handler processes multiple
+    * requests from different traces or the same trace.
+    *
+    * @param spanContext
+    *   the context of the linked span
+    *
+    * @param attributes
+    *   the set of attributes to associated with the link
+    */
+  inline def addLink(
+      spanContext: SpanContext,
+      attributes: Attribute[_]*
+  ): F[Unit] =
+    ${ SpanMacro.addLink('self, 'spanContext, 'attributes) }
+
+  /** Adds a link to the span.
+    *
+    * Links are used to link spans in different traces. Used (for example) in
+    * batching operations, where a single batch handler processes multiple
+    * requests from different traces or the same trace.
+    *
+    * @param spanContext
+    *   the context of the linked span
+    *
+    * @param attributes
+    *   the set of attributes to associated with the link
+    */
+  inline def addLink(
+      spanContext: SpanContext,
+      attributes: immutable.Iterable[Attribute[_]]
+  ): F[Unit] =
+    ${ SpanMacro.addLink('self, 'spanContext, 'attributes) }
+
   /** Records information about the `Throwable` to the span.
     *
     * @param exception
@@ -228,6 +264,17 @@ object SpanMacro {
       else $span.backend.meta.unit
     }
 
+  def addLink[F[_]](
+      span: Expr[Span[F]],
+      spanContext: Expr[SpanContext],
+      attributes: Expr[immutable.Iterable[Attribute[_]]]
+  )(using Quotes, Type[F]) =
+    '{
+      if ($span.backend.meta.isEnabled)
+        $span.backend.addLink($spanContext, $attributes)
+      else $span.backend.meta.unit
+    }
+
   def recordException[F[_]](
       span: Expr[Span[F]],
       exception: Expr[Throwable],

core/trace/src/main/scala/org/typelevel/otel4s/trace/Span.scala

@@ -141,6 +141,11 @@ object Span {
         attributes: immutable.Iterable[Attribute[_]]
     ): F[Unit]
 
+    def addLink(
+        spanContext: SpanContext,
+        attributes: immutable.Iterable[Attribute[_]]
+    ): F[Unit]
+
     def recordException(
         exception: Throwable,
         attributes: immutable.Iterable[Attribute[_]]
@@ -206,6 +211,11 @@ object Span {
             attributes: immutable.Iterable[Attribute[_]]
         ): F[Unit] = unit
 
+        def addLink(
+            spanContext: SpanContext,
+            attributes: immutable.Iterable[Attribute[_]]
+        ): F[Unit] = unit
+
         def recordException(
             exception: Throwable,
             attributes: immutable.Iterable[Attribute[_]]
@@ -239,6 +249,11 @@ object Span {
           attributes: immutable.Iterable[Attribute[_]]
       ): G[Unit] =
         f(backend.addEvent(name, timestamp, attributes))
+      def addLink(
+          spanContext: SpanContext,
+          attributes: immutable.Iterable[Attribute[_]]
+      ): G[Unit] =
+        f(backend.addLink(spanContext, attributes))
       def recordException(
           exception: Throwable,
           attributes: immutable.Iterable[Attribute[_]]

oteljava/trace/src/main/scala/org/typelevel/otel4s/oteljava/trace/SpanBackendImpl.scala

@@ -78,6 +78,18 @@ private[oteljava] class SpanBackendImpl[F[_]: Sync](
       ()
     }
 
+  def addLink(
+      spanContext: SpanContext,
+      attributes: immutable.Iterable[Attribute[_]]
+  ): F[Unit] =
+    Sync[F].delay {
+      jSpan.addLink(
+        SpanContextConversions.toJava(spanContext),
+        attributes.toJavaAttributes
+      )
+      ()
+    }
+
   def setStatus(status: StatusCode): F[Unit] =
     Sync[F].delay {
       jSpan.setStatus(toJStatus(status))

sdk/trace/src/main/scala/org/typelevel/otel4s/sdk/trace/SdkSpanBackend.scala

@@ -106,6 +106,14 @@ private final class SdkSpanBackend[F[_]: Monad: Clock: Console] private (
       EventData(name, timestamp, attributes.to(Attributes))
     )
 
+  def addLink(
+      context: SpanContext,
+      attributes: immutable.Iterable[Attribute[_]]
+  ): F[Unit] =
+    updateState("addLink") { s =>
+      s.copy(links = s.links :+ LinkData(context, attributes.to(Attributes)))
+    }.void
+
   def recordException(
       exception: Throwable,
       attributes: immutable.Iterable[Attribute[_]]
@@ -192,7 +200,7 @@ private final class SdkSpanBackend[F[_]: Monad: Clock: Console] private (
       status = state.status,
       attributes = state.attributes,
       events = state.events,
-      links = immutableState.links,
+      links = state.links,
       instrumentationScope = immutableState.scopeInfo,
       resource = immutableState.resource
     )
@@ -267,14 +275,14 @@ private object SdkSpanBackend {
         kind = kind,
         parentContext = parentContext,
         resource = resource,
-        links = links,
         startTimestamp = startTimestamp
       )
 
     val mutableState = MutableState(
       name = name,
       status = StatusData.Unset,
       attributes = attributes,
+      links = links,
       events = Vector.empty,
       endTimestamp = None
     )
@@ -293,7 +301,6 @@ private object SdkSpanBackend {
       kind: SpanKind,
       parentContext: Option[SpanContext],
       resource: TelemetryResource,
-      links: Vector[LinkData],
       startTimestamp: FiniteDuration
   )
 
@@ -304,6 +311,7 @@ private object SdkSpanBackend {
       status: StatusData,
       attributes: Attributes,
       events: Vector[EventData],
+      links: Vector[LinkData],
       endTimestamp: Option[FiniteDuration]
   )
 

sdk/trace/src/test/scala/org/typelevel/otel4s/sdk/trace/SdkSpanBackendSuite.scala

@@ -91,6 +91,21 @@ class SdkSpanBackendSuite extends CatsEffectSuite with ScalaCheckEffectSuite {
     }
   }
 
+  test(".addLink(:SpanContext, :Attribute[_]*)") {
+    PropF.forAllF { (spanContext: SpanContext, attrs: Attributes) =>
+      val link = LinkData(spanContext, attrs)
+
+      TestControl.executeEmbed {
+        for {
+          span <- start()
+          _ <- assertIO(span.toSpanData.map(_.links), Vector.empty)
+          _ <- span.addLink(spanContext, attrs)
+          _ <- assertIO(span.toSpanData.map(_.links), Vector(link))
+        } yield ()
+      }
+    }
+  }
+
   test(".updateName(:String)") {
     PropF.forAllF { (name: String, nextName: String) =>
       for {

sdk/trace/src/test/scala/org/typelevel/otel4s/sdk/trace/processor/SimpleSpanProcessorSuite.scala

@@ -169,6 +169,12 @@ class SimpleSpanProcessorSuite
       ): IO[Unit] =
         noopBackend.addEvent(name, timestamp, attributes)
 
+      def addLink(
+          spanContext: SpanContext,
+          attributes: immutable.Iterable[Attribute[_]]
+      ): IO[Unit] =
+        noopBackend.addLink(spanContext, attributes)
+
       def recordException(
           exception: Throwable,
           attributes: immutable.Iterable[Attribute[_]]