WordPress: only built plugin GPL licensed

Question

We are developing WordPress plugins. As WordPress itself is GPL licensed we must publish our plugin as GPL, too. Our complete plugin development environment is built on top of a lot of devDependencies and dependencies (npm with package.json). I did some tests with https://www.npmjs.com/package/licensee and the output gave me also dependencies licensed under CC-BY-3.0 and CC-BY-4.0.

The above mentioned CC dependencies are only represent in devDependencies, that means, the code of that dependencies are only used for building the plugin. In our CI/CD pipeline we get an installable and uploadable .zip file with the WordPress plugin itself as artifact.

• Is the build process itself (e. g webpack, babel or typescript) relevant for the built WordPress plugin? Can I differentiate between licensing of dependencies and devDependencies? Do I need to make the build process also GPL?
• I need to put a file like 3RD_PARTY_LICENSES to the built artifact. Do I need to refer to all used dependencies (inclusive devDependencies)?

Answer 1

For copyright licensing, only the dependencies of the deployed software are relevant. The licenses on your build tools can be completely ignored¹.

A file like 3RD_PARTY_LICENSES also only needs to refer to the licenses of your dependencies.

^{1: the exception here are tools that copy part of their source into the output. Those would effectively be a dependency of the deployed software.}