Plexus and Maven

Prior to Maven 3.9, a component named plexus-tools was included by Apache Maven at runtime. The component is used by Maven plugin internals. In v3.9.0 of Maven, this was removed. Some older Maven plugins may still need this dependency to work. The protobuf-maven-plugin does not require this to operate in normal cases.

Under some conditions, it appears that the use of certain other plugins or extensions triggers an issue within Maven where plexus-utils becomes a requirement. A current known case occurs when users make use of the Maven Cache Extension. The following error may be observed if this issue is encountered:

[ERROR] org.apache.maven.plugin.PluginContainerException: Unable to load the mojo 'generate' (or one of its required components) from the plugin 'io.github.ascopes:protobuf-maven-plugin:2.7.0': com.google.inject.ProvisionException: Unable to provision, see the following errors:
[ERROR] 
[ERROR] 1) [Guice/ErrorInCustomProvider]: IllegalStateException
[ERROR]   at MojoExecutionScopeModule.configure(MojoExecutionScopeModule.java:50)
[ERROR]       \_ installed by: WireModule -> MojoExecutionScopeModule
[ERROR]   at TemporarySpace.<init>(TemporarySpace.java:45)
[ERROR]       \_ for 2nd parameter
[ERROR]   at UrlResourceFetcher.<init>(UrlResourceFetcher.java:65)
[ERROR]       \_ for 1st parameter
[ERROR]   at ProtocResolver.<init>(ProtocResolver.java:63)
[ERROR]       \_ for 5th parameter
[ERROR]   at ProtobufBuildOrchestrator.<init>(ProtobufBuildOrchestrator.java:71)
[ERROR]       \_ for 2nd parameter
[ERROR]   at AbstractGenerateMojo.sourceCodeGenerator(AbstractGenerateMojo.java:71)
[ERROR]       \_ for field sourceCodeGenerator
[ERROR]   while locating MainGenerateMojo
[ERROR]   at ClassRealm[plugin>io.github.ascopes:protobuf-maven-plugin:2.7.0, parent: ClassLoaders$AppClassLoader@531d72ca]
[ERROR]       \_ installed by: WireModule -> PlexusBindingModule
[ERROR]   while locating Mojo annotated with @Named("io.github.ascopes:protobuf-maven-plugin:2.7.0:generate")

Note that other errors like this may also occur.

The workaround for now appears to be to include plexus-utils explicitly as a dependency of this plugin:

<plugin>
  <groupId>io.github.ascopes</groupId>
  <artifactId>protobuf-maven-plugin</artifactId>
  <version>...</version>

  <configuration>...</configuration>
  <executions>...</executions>

  <dependencies>
    <dependency>
      <groupId>org.codehaus.plexus</groupId>
      <artifactId>plexus-utils</artifactId>
      <version>4.0.2</version>
    </dependency>
  </dependencies>
</plugin>

• See https://github.com/ascopes/protobuf-maven-plugin/issues/472 for tracking this issue.

Incremental compilation with descriptor files

Using incremental compilation when creating descriptor files is not supported due to limitations with protoc. The entire descriptor must be rebuilt on each build to remain valid.

As of 2.10.0, incremental compilation will be disabled automatically if this condition is detected.