[BUG] Mapstruct processor dependency is deleted

[afillatre]

Describe the bug
After depclean completes, and given mapstruct processor is used, the mapstruct-processor direct dependency is not longer present on the debloated pom.xml

To Reproduce
Steps to reproduce the behavior:

1. Configure the maven-processor-plugin to use the mapstruct annotation

      <plugin>
        <groupId>org.bsc.maven</groupId>
        <artifactId>maven-processor-plugin</artifactId>
        <executions>
          <execution>
            <id>process</id>
            <goals>
              <goal>process</goal>
            </goals>
            <phase>generate-sources</phase>
            <configuration>
              <processors>
                <processor>org.mapstruct.ap.MappingProcessor</processor>
              </processors>
            </configuration>
          </execution>
        </executions>
      </plugin>

2. Add required mapstruct dependencies

    <dependency>
      <groupId>org.mapstruct</groupId>
      <artifactId>mapstruct</artifactId>
    </dependency>
    <dependency>
      <groupId>org.mapstruct</groupId>
      <artifactId>mapstruct-processor</artifactId>
      <scope>provided</scope>
    </dependency>

3. Run depclean with debloated-pom generation

Expected behavior
mapstruct-processor dependency is conserved

Additional context
Mapstruct generates code during the generated-sources phase, but do not keep mapstruct-processor imports in the generated classes. This may be why it is eventually removed from the debloated-pom.

One could manually list this dependency into the ignoreDependencies configuration, but it may be better to consider annotation processor classes to be rightful provided dependencies

[cesarsotovalero]

Hi @afillatre, thanks for reporting this issue.

Can you please give more details about your proposal?

... but it may be better to consider annotation processor classes to be rightful provided dependencies

[afillatre]

Yes. Given this plugin configuration

      <plugin>
        <groupId>org.bsc.maven</groupId>
        <artifactId>maven-processor-plugin</artifactId>
        <executions>
          <execution>
            <id>process</id>
            <goals>
              <goal>process</goal>
            </goals>
            <phase>generate-sources</phase>
            <configuration>
              <processors>
                <processor>org.mapstruct.ap.MappingProcessor</processor>
              </processors>
            </configuration>
          </execution>
        </executions>
      </plugin>

Depclean could consider org.mapstruct.ap.MappingProcessor to be rightfully part of the project, and add it to the Dependency Usage Analysis, because it is declared in the pom as a processor

[cesarsotovalero]

Hi@afillatre, I understand your proposal.

It is definitely not difficult to implement some rules that analyze the xml pom to consider this and other similar usage cases. Thus, excluding some false positives (such as in the case of processors).

I'll implement the pom rule parser ASAP.

In case you feel comfortable with the task, the debloated-pom is generated here: https://github.com/castor-software/depclean/blob/master/depclean-maven-plugin/src/main/java/se/kth/depclean/DepCleanMojo.java#L586-L658.