PMD fails with custom rulesets for project with multiple modules

How to define custom-rulesets.xml in parent project, so it is re-used in children modules?

I have a PMD example project that works well (you can check later).

However, this maven project does not have children.

Project structure

pmd-java-14-example _.
                     |_ core
                     |_ tasks

custom-rulesets.xml

<?xml version="1.0"?>

<!-- https://github.com/pmd/pmd/blob/master/pmd-java/src/main/resources/rulesets/java/basic.xml -->
<!-- https://pmd.github.io/pmd/pmd_rules_java_codestyle.html#shortvariable -->
<ruleset
        name="custom-ruleset"
        xmlns="http://pmd.sourceforge.net/ruleset/2.0.0">
    <description>
        The Basic ruleset contains a collection of good practices which should be followed.
    </description>

    <rule ref="category/java/design.xml/SimplifiedTernary"/>
    <rule ref="category/java/codestyle.xml/MethodArgumentCouldBeFinal"/>
    <rule ref="category/java/codestyle.xml/LocalVariableCouldBeFinal"/>
    <rule ref="category/java/errorprone.xml/AvoidDecimalLiteralsInBigDecimalConstructor"/>
    <rule ref="category/java/bestpractices.xml/UnusedLocalVariable"/>
    <rule ref="category/java/bestpractices.xml/UnusedPrivateField"/>
    <rule ref="category/java/codestyle.xml/DuplicateImports"/>
    <rule ref="category/java/codestyle.xml/ShortMethodName"/>
    <rule ref="category/java/codestyle.xml/ShortVariable"/>
</ruleset>

When I have a parent pom and a child module, pmd fails for the child module, because it cannot find custom-rulesets.xml.

pom.xml (parent pom that has a child module).

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns="http://maven.apache.org/POM/4.0.0"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.yk.utils</groupId>
    <artifactId>pmd-java-14-example</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>


    <properties>
        <java.version>14</java.version>
        <maven.compiler.source>${java.version}</maven.compiler.source>
        <maven.compiler.target>${java.version}</maven.compiler.target>

        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>

        <pmd.plugin.version>3.13.0</pmd.plugin.version>
        <pmd.core.version>6.23.0</pmd.core.version>
    </properties>


	<modules>
        <module>core</module>
        <module>tasks</module>
    </modules>

    <dependencies>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.1.7</version>
        </dependency>
    </dependencies>


    <reporting>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jxr-plugin</artifactId>
                <version>3.0.0</version>
            </plugin>
        </plugins>
    </reporting>

    <build>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-pmd-plugin</artifactId>
                    <version>${pmd.plugin.version}</version>
                </plugin>
            </plugins>
        </pluginManagement>

        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-pmd-plugin</artifactId>
                <configuration>
                    <failOnViolation>true</failOnViolation>
                    <printFailingErrors>true</printFailingErrors>
                    <targetJdk>${java.version}</targetJdk>


                    <rulesets>
                        <!-- https://maven.apache.org/plugins/maven-pmd-plugin/examples/usingRuleSets.html -->
                        <ruleset>/rulesets/java/maven-pmd-plugin-default.xml</ruleset>

                        <!-- https://github.com/pmd/pmd/blob/master/pmd-java/src/main/resources/rulesets/java/basic.xml -->
                        <!-- https://github.com/pmd/pmd/blob/master/pmd-core/src/main/resources/rulesets/internal/all-java.xml -->
                        <ruleset>/category/java/bestpractices.xml</ruleset>
                        <ruleset>
                            custom-ruleset.xml
                        </ruleset>
                    </rulesets>
                </configuration>
                <executions>
                    <execution>
                        <id>check pmd and fail</id>
                        <phase>package</phase>
                        <goals>
                            <goal>check</goal>
                        </goals>
                    </execution>
                </executions>

                <dependencies>
                    <dependency>
                        <groupId>net.sourceforge.pmd</groupId>
                        <artifactId>pmd-java</artifactId>
                        <version>${pmd.core.version}</version>
                    </dependency>

                    <dependency>
                        <groupId>net.sourceforge.pmd</groupId>
                        <artifactId>pmd-core</artifactId>
                        <version>${pmd.core.version}</version>
                    </dependency>
                </dependencies>
            </plugin>


            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-site-plugin</artifactId>
                <version>3.9.0</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-project-info-reports-plugin</artifactId>
                <version>3.0.0</version>
            </plugin>
        </plugins>
    </build>
</project>

The difference is that now the pom has child modules and <packaging>pom</packaging>.

This part fails mvn clean install

<ruleset>custom-ruleset.xml</ruleset>

Error messages

[INFO]
[INFO] pmd-java-14-example ................................ SUCCESS [  0.922 s]
[INFO] core ............................................... FAILURE [  1.929 s]
[INFO] tasks .............................................. SKIPPED
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  2.980 s
[INFO] Finished at: 2020-05-03T13:15:45+02:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-pmd-plugin:3.13.0:pmd (pmd) on project bst-core: Execution pmd of goal org.apache.maven.plugins:maven-pmd-plugin:3.13.0:pmd failed: org.apache.maven.reporting.MavenReport
Exception: Could not find resource 'pmd-java-14-example\core\custom-ruleset.xml'. -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.

What I tried

As I understand, maven uses custom-rulesets.xml file for parent modules - it is successful, then it tries to use this file for child module, and of course, this file is not present in the child module.

I tried to set a property - absolute path to the location of custom-rulesets.xml. It works, however, I cannot push it into github.

I can also push this custom rule set to git hub and add a link to github repository and file and use it.
This is a better alternative.

And of course, I do not want to copy-paste this file across different children modules.

I would suggest that you place your rulesets outside the Maven projects, like you are doing for the other rulesets.

The question is whether your custom ruleset should only be checked for those child modules in that project. Or is it rather something you would like to check for all Java modules?

If you want to check all your Java modules, just add the ruleset with its absolute path to your existing PMD plugin configuration. The PMD plugin ignores POM projects.

If it's a specific ruleset for just that project and just those child modules, I would configure that in the parent project (the POM project).

Please, post your answers because this is a quick work-around which I need now!

<ruleset>../custom-ruleset.xml</ruleset>.

Explanation, my project structure is one parent that has two children modules. As the children are on the same level in the directory tree, ../ thus it works.

However, it will not work, if there is src folder in parent, or if a child module has children as well.