NIFI-14073 Add PMD Plugin to contrib-check Profile

[exceptionfactory]

Summary

NIFI-14073 Adds the Maven PMD Plugin to the set of plugins run as part of the contrib-check profile for verifying correctness and style of code changes.

The PMD project augments existing code style evaluation from Checkstyle and introduces tuned analysis rules for catching common problems.

Thanks to recent efforts to cleanup and standardize code across the repository, the changes in this pull request are limited to bringing a handful of classes in line with common rules. Most of these changes involve removing or annotating unused private fields, and bringing consistency to the use of generic types.

The plugin configuration uses the pmd-ruleset.xml, which is based on the default set of rules, but removes some that would have involved too many changes to existing code. The PMD configuration excludes code generated from ANTLR and JAXB plugins from evaluation.

Additional changes include simplifying the Maven options for the GitHub ci-workflow, removing the need for selective exclusion of certain modules. These adjustments make it easier to run the pmd:check goal without a large number of module exclusions.

Tracking

Please complete the following tracking steps prior to pull request creation.

Issue Tracking

• Apache NiFi Jira issue created

Pull Request Tracking

• Pull Request title starts with Apache NiFi Jira issue number, such as NIFI-00000
• Pull Request commit message starts with Apache NiFi Jira issue number, as such NIFI-00000

Pull Request Formatting

• Pull Request based on current revision of the main branch
• Pull Request refers to a feature branch with one commit containing changes

Verification

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Build

• Build completed using mvn clean install -P contrib-check
  • JDK 21

Licensing

• New dependencies are compatible with the Apache License 2.0 according to the License Policy
• New dependencies are documented in applicable LICENSE and NOTICE files

Documentation

• Documentation formatting appears as expected in rendered files

[exceptionfactory]

@dan-s1 Thanks for your recent working on standardizing use of the diamond operator for generic types. I included the UseDiamondOperator rule in the list of PMD rules, which enforces standardized usage. Adding the PMD plugin to the set of tools for evaluation will avoid regressions in this and other areas.

[pvillard31]

Thanks for the changes @exceptionfactory, great addition for maintaining good code quality.

[dan-s1]

@dan-s1 Thanks for your recent working on standardizing use of the diamond operator for generic types. I included the UseDiamondOperator rule in the list of PMD rules, which enforces standardized usage. Adding the PMD plugin to the set of tools for evaluation will avoid regressions in this and other areas.

@exceptionfactory Thank you for the including this and thank you for contributing this PR to introduce the enforcement of these standard rules. It certainly brings an increased rigor to the code.
I am sorry I did not get a chance to review this PR but I was curios which rules "would have involved too many changes to existing code"? Is that something which can be taken on in future PRs?

[exceptionfactory]

@dan-s1 For reference, here is the default ruleset configuration for the Maven PMD plugin:

https://github.com/apache/maven-pmd-plugin/blob/master/src/main/resources/rulesets/java/maven-pmd-plugin-default.xml

Most of the removed rulesets relate to unused elements and unnecessary syntax.

Removing unused values involves code changes in cases that may impact behavior, so that was the reason for removing some of those rules.

Removing unnecessary syntax should be safer in general, but touches more files.

Now that the PMD check is part of the main branch, we can certainly consider adding some of these rulesets on a case-by-case basis.