Change B3 extraction format to single

See gh-36061

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

@@ -124,7 +124,7 @@ class CompositePropagationFactory extends Propagation.Factory {
 		 * @return the B3 propagation factory
 		 */
 		private Propagation.Factory b3Single() {
-			return B3Propagation.newFactoryBuilder().injectFormat(B3Propagation.Format.SINGLE_NO_PARENT).build();
+			return B3Propagation.newFactoryBuilder().injectFormat(B3Propagation.Format.SINGLE).build();
 		}
 
 		/**

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

@@ -17,7 +17,9 @@
 package org.springframework.boot.actuate.autoconfigure.tracing;
 
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.stream.Stream;
 
 import brave.Span;
@@ -31,6 +33,7 @@ import brave.propagation.CurrentTraceContext;
 import brave.propagation.CurrentTraceContext.ScopeDecorator;
 import brave.propagation.Propagation;
 import brave.propagation.Propagation.Factory;
+import brave.propagation.TraceContext;
 import brave.sampler.Sampler;
 import io.micrometer.tracing.brave.bridge.BraveBaggageManager;
 import io.micrometer.tracing.brave.bridge.BraveSpanCustomizer;
@@ -152,6 +155,31 @@ class BraveAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	void shouldUseB3SingleWithParentWhenPropagationTypeIsB3() {
+		this.contextRunner
+			.withPropertyValues("management.tracing.propagation.type=B3", "management.tracing.sampling.probability=1.0")
+			.run((context) -> {
+				Propagation<String> propagation = context.getBean(Factory.class).get();
+				Tracer tracer = context.getBean(Tracing.class).tracer();
+				Span child;
+				Span parent = tracer.nextSpan().name("parent");
+				try (Tracer.SpanInScope ignored = tracer.withSpanInScope(parent.start())) {
+					child = tracer.nextSpan().name("child");
+					child.start().finish();
+				}
+				finally {
+					parent.finish();
+				}
+
+				Map<String, String> map = new HashMap<>();
+				TraceContext childContext = child.context();
+				propagation.injector(this::injectToMap).inject(childContext, map);
+				assertThat(map).containsExactly(Map.entry("b3", "%s-%s-1-%s".formatted(childContext.traceIdString(),
+						childContext.spanIdString(), childContext.parentIdString())));
+			});
+	}
+
 	@Test
 	void shouldNotSupplyCorrelationScopeDecoratorIfBaggageDisabled() {
 		this.contextRunner.withPropertyValues("management.tracing.baggage.enabled=false")
@@ -313,6 +341,10 @@ class BraveAutoConfigurationTests {
 		});
 	}
 
+	private void injectToMap(Map<String, String> map, String key, String value) {
+		map.put(key, value);
+	}
+
 	private List<Factory> getInjectors(Factory factory) {
 		assertThat(factory).as("factory").isNotNull();
 		if (factory instanceof CompositePropagationFactory compositePropagationFactory) {