Fix gRPC auto-configuration when protobuf is used without gRPC

build-plugin/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/ProtobufPluginAction.java

@@ -30,6 +30,7 @@
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
 import org.gradle.api.artifacts.Configuration;
+import org.gradle.api.artifacts.Dependency;
 import org.gradle.api.artifacts.DependencyResolveDetails;
 import org.gradle.api.artifacts.ModuleVersionSelector;
 import org.gradle.api.artifacts.component.ModuleComponentIdentifier;
@@ -62,11 +63,27 @@ public Class<? extends Plugin<? extends Project>> getPluginClass() {
 	public void execute(Project project) {
 		ProtobufExtension protobuf = project.getExtensions().getByType(ProtobufExtension.class);
 		protobuf.protoc(this::configureProtoc);
-		protobuf.plugins(this::configurePlugins);
-		protobuf.generateProtoTasks(this::configureGenerateProtoTasks);
 		project.getConfigurations()
 			.named(this::isProtobufToolsLocator)
 			.configureEach((configuration) -> configureProtobufToolsLocator(project, configuration));
+		// gRPC plugin configuration is deferred so we can check if gRPC is actually
+		// declared as a dependency before registering the protoc-gen-grpc-java artifact.
+		// Without this guard, Gradle would try to resolve io.grpc:protoc-gen-grpc-java:null
+		// for projects that use protobuf but not gRPC.
+		project.afterEvaluate((p) -> {
+			if (hasGrpcDependency(p)) {
+				protobuf.plugins(this::configurePlugins);
+				protobuf.generateProtoTasks(this::configureGenerateProtoTasks);
+			}
+		});
+	}
+
+	private boolean hasGrpcDependency(Project project) {
+		return project.getConfigurations()
+			.stream()
+			.flatMap((configuration) -> configuration.getDependencies().stream())
+			.map(Dependency::getGroup)
+			.anyMatch("io.grpc"::equals);
 	}
 
 	private void configureProtoc(ExecutableLocator protoc) {

build-plugin/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/plugin/ProtobufPluginActionIntegrationTests.java

@@ -94,7 +94,12 @@ void usesVersionOfProtocDependencyWhenSpecified() {
 	void usesVersionOfGrpcPluginDependencyWhenSpecified() {
 		assertThat(this.gradleBuild.build("dependencies", "--configuration", "protobufToolsLocator_grpc").getOutput())
 			.contains("io.grpc:protoc-gen-grpc-java:1.78.0");
+	}
 
+	@TestTemplate
+	void doesNotConfigureGrpcWhenGrpcIsNotPresent() {
+		assertThat(this.gradleBuild.build("grpcNotConfigured").getOutput())
+			.contains("grpc tools locator present: false");
 	}
 
 }

build-plugin/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/plugin/ProtobufPluginActionIntegrationTests-doesNotConfigureGrpcWhenGrpcIsNotPresent.gradle

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2012-present 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.
+ */
+
+plugins {
+	id 'org.springframework.boot' version '{version}'
+	id 'java'
+}
+
+apply plugin: 'com.google.protobuf'
+
+group = 'com.example'
+version = '0.0.1'
+
+repositories {
+	mavenCentral()
+}
+
+dependencies {
+	implementation("com.google.protobuf:protobuf-java:4.34.0")
+}
+
+tasks.register("grpcNotConfigured") {
+	doFirst {
+		def hasGrpcToolsLocator = project.configurations.names.any { it == "protobufToolsLocator_grpc" }
+		println "grpc tools locator present: $hasGrpcToolsLocator"
+	}
+}

module/spring-boot-test-classic-modules/build.gradle

@@ -67,9 +67,6 @@ dependencies {
 	api(project(":module:spring-boot-graphql-test")) {
 		transitive = false
 	}
-	api(project(":module:spring-boot-grpc-test")) {
-		transitive = false
-	}
 	api(project(":module:spring-boot-jdbc-test")) {
 		transitive = false
 	}