maven how to start plugin goals individually

　　I'm annoyed, I searched the Internet for a long time and couldn't find it

　　It turns out that the plug-in name does not need to be defined but is directly imagined. As follows, I have tried several

　　mvn plugin:goal has not been successful; from the code, there is no doubt about the goal, it is compile, but which is the plugin?

　　protobuf

　　protobuf

　　protobuf

　　protobuf
　　

  <plugins>
            <plugin>
                <groupId>org.xolstice.maven.plugins</groupId>
                <artifactId>protobuf-maven-plugin</artifactId>
                <version>0.5.1</version>
                <configuration>
                    <protocArtifact>com.google.protobuf:protoc:3.5.1-1:exe:${os.detected.classifier}</protocArtifact>
                    <pluginId>grpc-java</pluginId>
                    <pluginArtifact>io.grpc:protoc-gen-grpc-java:1.11.0:exe:${os.detected.classifier}</pluginArtifact>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                            <goal>compile-custom</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>

　　So just execute mvn protobuf : compile

　　But why doesn't maven represent the plugin name in metadata?