Introduce ObservationHandlerGroup interface

Add a new `ObservationHandlerGroup` interface that allows grouping
logic to be implemented by the metrics and tracing modules. This
update removes the need for `ObservabilityAutoConfiguration`.

Issue: 45746

Author: philwebb

spring-boot-project/spring-boot-actuator-autoconfigure-all/src/main/java/org/springframework/boot/actuate/autoconfigure/observability/ObservabilityAutoConfiguration.java

@@ -27,6 +27,7 @@
 import io.micrometer.tracing.handler.DefaultTracingObservationHandler;
 import io.micrometer.tracing.handler.PropagatingReceiverTracingObservationHandler;
 import io.micrometer.tracing.handler.PropagatingSenderTracingObservationHandler;
+import io.micrometer.tracing.handler.TracingObservationHandler;
 import io.micrometer.tracing.propagation.Propagator;
 import org.aspectj.weaver.Advice;
 
@@ -37,6 +38,7 @@
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBooleanProperty;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.observation.autoconfigure.ObservationHandlerGroup;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.Ordered;
@@ -45,6 +47,7 @@
 import org.springframework.expression.ExpressionParser;
 import org.springframework.expression.spel.standard.SpelExpressionParser;
 import org.springframework.expression.spel.support.SimpleEvaluationContext;
+import org.springframework.util.ClassUtils;
 
 /**
  * {@link EnableAutoConfiguration Auto-configuration} for the Micrometer Tracing API.
@@ -54,7 +57,6 @@
  * @since 3.0.0
  */
 @AutoConfiguration
-@ConditionalOnClass(Tracer.class)
 @ConditionalOnBean(Tracer.class)
 public class MicrometerTracingAutoConfiguration {
 
@@ -75,6 +77,13 @@ public class MicrometerTracingAutoConfiguration {
 	 */
 	public static final int SENDER_TRACING_OBSERVATION_HANDLER_ORDER = 2000;
 
+	@Bean
+	public ObservationHandlerGroup tracingObservationHandlerGroup(Tracer tracer) {
+		return ClassUtils.isPresent("io.micrometer.core.instrument.MeterRegistry", null)
+				? new TracingAndMeterObservationHandlerGroup(tracer)
+				: ObservationHandlerGroup.of(TracingObservationHandler.class);
+	}
+
 	@Bean
 	@ConditionalOnMissingBean
 	@Order(DEFAULT_TRACING_OBSERVATION_HANDLER_ORDER)

spring-boot-project/spring-boot-actuator-autoconfigure-all/src/main/java/org/springframework/boot/actuate/autoconfigure/observability/package-info.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright 2012-2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.autoconfigure.tracing;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import io.micrometer.core.instrument.observation.MeterObservationHandler;
+import io.micrometer.observation.ObservationHandler;
+import io.micrometer.observation.ObservationHandler.FirstMatchingCompositeObservationHandler;
+import io.micrometer.observation.ObservationRegistry.ObservationConfig;
+import io.micrometer.tracing.Tracer;
+import io.micrometer.tracing.handler.TracingAwareMeterObservationHandler;
+import io.micrometer.tracing.handler.TracingObservationHandler;
+
+import org.springframework.boot.observation.autoconfigure.ObservationHandlerGroup;
+
+/**
+ * {@link ObservationHandlerGroup} that considers both {@link TracingObservationHandler}
+ * and {@link MeterObservationHandler} types as members. This group takes precedence over
+ * any regular {@link MeterObservationHandler} group in order to use ensure
+ * {@link TracingAwareMeterObservationHandler} wrapping is applied during registration.
+ *
+ * @author Phillip Webb
+ */
+class TracingAndMeterObservationHandlerGroup implements ObservationHandlerGroup {
+
+	private final Tracer tracer;
+
+	TracingAndMeterObservationHandlerGroup(Tracer tracer) {
+		this.tracer = tracer;
+	}
+
+	@Override
+	public boolean isMember(ObservationHandler<?> handler) {
+		return MeterObservationHandler.class.isInstance(handler) || TracingObservationHandler.class.isInstance(handler);
+	}
+
+	@Override
+	public int compareTo(ObservationHandlerGroup other) {
+		if (other instanceof TracingAndMeterObservationHandlerGroup) {
+			return 0;
+		}
+		return MeterObservationHandler.class.isAssignableFrom(other.handlerType()) ? -1 : 1;
+	}
+
+	@Override
+	public void registerMembers(ObservationConfig config, List<ObservationHandler<?>> members) {
+		List<ObservationHandler<?>> tracingHandlers = new ArrayList<>(members.size());
+		List<ObservationHandler<?>> metricsHandlers = new ArrayList<>(members.size());
+		for (ObservationHandler<?> member : members) {
+			if (member instanceof MeterObservationHandler<?> meterObservationHandler
+					&& !(member instanceof TracingAwareMeterObservationHandler<?>)) {
+				metricsHandlers.add(new TracingAwareMeterObservationHandler<>(meterObservationHandler, this.tracer));
+			}
+			else {
+				tracingHandlers.add(member);
+			}
+		}
+		registerHandlers(config, tracingHandlers);
+		registerHandlers(config, metricsHandlers);
+	}
+
+	private void registerHandlers(ObservationConfig config, List<ObservationHandler<?>> handlers) {
+		if (handlers.size() == 1) {
+			config.observationHandler(handlers.get(0));
+		}
+		else if (!handlers.isEmpty()) {
+			config.observationHandler(new FirstMatchingCompositeObservationHandler(handlers));
+		}
+	}
+
+	@Override
+	public Class<?> handlerType() {
+		return TracingObservationHandler.class;
+	}
+
+}

spring-boot-project/spring-boot-actuator-autoconfigure-all/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/MicrometerTracingAutoConfiguration.java

@@ -1,6 +1,5 @@
 org.springframework.boot.actuate.autoconfigure.cloudfoundry.reactive.ReactiveCloudFoundryActuatorAutoConfiguration
 org.springframework.boot.actuate.autoconfigure.cloudfoundry.servlet.CloudFoundryActuatorAutoConfiguration
-org.springframework.boot.actuate.autoconfigure.observability.ObservabilityAutoConfiguration
 org.springframework.boot.actuate.autoconfigure.security.reactive.ReactiveManagementWebSecurityAutoConfiguration
 org.springframework.boot.actuate.autoconfigure.security.servlet.ManagementWebSecurityAutoConfiguration
 org.springframework.boot.actuate.autoconfigure.tracing.BraveAutoConfiguration