Add configuration property to enable micrometer annotations

Prior to this commit, the Micrometer annotations support (`@Timed`,
`@Counted`...) was guarded by the presence of both Micrometer and
AspectJ on the classpath.

This signal is too weak, considering the startup performance impact and
the fact that the AspectJ dependency can be brought transitively in many
cases.

This commit adds a new `micrometer.observations.annotations.enabled`
property that is set to `false` by default to only process the
annotations support when this property is enabled.

Fixes gh-39128

Author: bclozel

buildSrc/src/main/java/org/springframework/boot/build/context/properties/DocumentConfigurationProperties.java

@@ -215,6 +215,7 @@ private void rsocketPrefixes(Config prefix) {
 
 	private void actuatorPrefixes(Config prefix) {
 		prefix.accept("management");
+		prefix.accept("micrometer");
 	}
 
 	private void dockerComposePrefixes(Config prefix) {

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/MetricsAspectsAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -28,6 +28,7 @@
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.context.annotation.Bean;
 
 /**
@@ -39,6 +40,7 @@
  */
 @AutoConfiguration(after = { MetricsAutoConfiguration.class, CompositeMeterRegistryAutoConfiguration.class })
 @ConditionalOnClass({ MeterRegistry.class, Advice.class })
+@ConditionalOnProperty(prefix = "micrometer.observations.annotations", name = "enabled", havingValue = "true")
 @ConditionalOnBean(MeterRegistry.class)
 public class MetricsAspectsAutoConfiguration {
 

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -35,6 +35,7 @@
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.Ordered;
@@ -96,6 +97,7 @@ public PropagatingReceiverTracingObservationHandler<?> propagatingReceiverTracin
 
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(Advice.class)
+	@ConditionalOnProperty(prefix = "micrometer.observations.annotations", name = "enabled", havingValue = "true")
 	static class SpanAspectConfiguration {
 
 		@Bean

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -2229,6 +2229,12 @@
       "defaultValue": [
         "W3C"
       ]
+    },
+    {
+      "name": "micrometer.observations.annotations.enabled",
+      "type": "java.lang.Boolean",
+      "description": "Whether auto-configuration of Micrometer annotations is enabled.",
+      "defaultValue": false
     }
   ],
   "hints": [

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/MetricsAspectsAutoConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -41,8 +41,19 @@
 class MetricsAspectsAutoConfigurationTests {
 
 	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner().with(MetricsRun.simple())
+		.withPropertyValues("micrometer.observations.annotations.enabled=true")
 		.withConfiguration(AutoConfigurations.of(MetricsAspectsAutoConfiguration.class));
 
+	@Test
+	void shouldNotConfigureAspectsByDefault() {
+		new ApplicationContextRunner().with(MetricsRun.simple())
+			.withConfiguration(AutoConfigurations.of(MetricsAspectsAutoConfiguration.class))
+			.run((context) -> {
+				assertThat(context).doesNotHaveBean(CountedAspect.class);
+				assertThat(context).doesNotHaveBean(TimedAspect.class);
+			});
+	}
+
 	@Test
 	void shouldConfigureAspects() {
 		this.contextRunner.run((context) -> {
@@ -78,11 +89,12 @@ void shouldNotConfigureAspectsIfAspectjIsMissing() {
 
 	@Test
 	void shouldNotConfigureAspectsIfMeterRegistryBeanIsMissing() {
-		new ApplicationContextRunner().run((context) -> {
-			assertThat(context).doesNotHaveBean(MeterRegistry.class);
-			assertThat(context).doesNotHaveBean(CountedAspect.class);
-			assertThat(context).doesNotHaveBean(TimedAspect.class);
-		});
+		new ApplicationContextRunner().withConfiguration(AutoConfigurations.of(MetricsAspectsAutoConfiguration.class))
+			.run((context) -> {
+				assertThat(context).doesNotHaveBean(MeterRegistry.class);
+				assertThat(context).doesNotHaveBean(CountedAspect.class);
+				assertThat(context).doesNotHaveBean(TimedAspect.class);
+			});
 	}
 
 	@Test

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/tracing/MicrometerTracingAutoConfigurationTests.java

@@ -47,15 +47,18 @@
  *
  * @author Moritz Halbritter
  * @author Jonatan Ivanov
+ * @author Brian Clozel
  */
 class MicrometerTracingAutoConfigurationTests {
 
 	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+		.withPropertyValues("micrometer.observations.annotations.enabled=true")
 		.withConfiguration(AutoConfigurations.of(MicrometerTracingAutoConfiguration.class));
 
 	@Test
 	void shouldSupplyBeans() {
 		this.contextRunner.withUserConfiguration(TracerConfiguration.class, PropagatorConfiguration.class)
+			.withPropertyValues("micrometer.observations.annotations.enabled=true")
 			.run((context) -> {
 				assertThat(context).hasSingleBean(DefaultTracingObservationHandler.class);
 				assertThat(context).hasSingleBean(PropagatingReceiverTracingObservationHandler.class);
@@ -127,6 +130,17 @@ void shouldNotSupplyBeansIfTracerIsMissing() {
 		});
 	}
 
+	@Test
+	void shouldNotSupplyAspectBeansIfPropertyIsDisabled() {
+		this.contextRunner.withUserConfiguration(TracerConfiguration.class, PropagatorConfiguration.class)
+			.withPropertyValues("micrometer.observations.annotations.enabled=false")
+			.run((context) -> {
+				assertThat(context).doesNotHaveBean(DefaultNewSpanParser.class);
+				assertThat(context).doesNotHaveBean(ImperativeMethodInvocationProcessor.class);
+				assertThat(context).doesNotHaveBean(SpanAspect.class);
+			});
+	}
+
 	@Test
 	void shouldNotSupplyBeansIfAspectjIsMissing() {
 		this.contextRunner.withUserConfiguration(TracerConfiguration.class)

spring-boot-project/spring-boot-docs/src/docs/asciidoc/actuator/metrics.adoc

@@ -1067,7 +1067,8 @@ Metrics for Jetty's `Connector` instances are bound by using Micrometer's `Jetty
 
 [[actuator.metrics.supported.timed-annotation]]
 ==== @Timed Annotation Support
-To use `@Timed` where it is not directly supported by Spring Boot, refer to the {micrometer-concepts-docs}#_the_timed_annotation[Micrometer documentation].
+To enable scanning of `@Timed` annotations, you will need to set the configprop:micrometer.observations.annotations.enabled[] property to `true`.
+Please refer to the {micrometer-concepts-docs}#_the_timed_annotation[Micrometer documentation].
 
 
 

spring-boot-project/spring-boot-docs/src/docs/asciidoc/actuator/observability.adoc

@@ -85,3 +85,11 @@ NOTE: Spring Boot does not provide auto-configuration for OpenTelemetry metrics
 OpenTelemetry tracing is only auto-configured when used together with <<actuator#actuator.micrometer-tracing, Micrometer Tracing>>.
 
 The next sections will provide more details about logging, metrics and traces.
+
+
+
+[[actuator.observability.annotations]]
+=== Micrometer Observation Annotations support
+
+To enable scanning of metrics and tracing annotations like `@Timed`, `@Counted`, `@MeterTag` and `@NewSpan` annotations, you will need to set the configprop:micrometer.observations.annotations.enabled[] property to `true`.
+This feature is supported Micrometer directly, please refer to the {micrometer-concepts-docs}#_the_timed_annotation[Micrometer] and {micrometer-tracing-docs}/api.html#_aspect_oriented_programming[Micrometer Tracing] reference docs.

spring-boot-project/spring-boot-docs/src/docs/asciidoc/attributes.adoc

@@ -109,6 +109,7 @@
 :micrometer-docs: https://micrometer.io/docs
 :micrometer-concepts-docs: {micrometer-docs}/concepts
 :micrometer-registry-docs: {micrometer-docs}/registry
+:micrometer-tracing-docs: https://docs.micrometer.io/tracing/reference
 :tomcat-docs: https://tomcat.apache.org/tomcat-{tomcat-version}-doc
 :graal-version: 22.3
 :graal-native-image-docs: https://www.graalvm.org/{graal-version}/reference-manual/native-image