This PR obsoletes #1769 . It applies on master and can be merged to pmd/7.0.x as well - it should work on the pmd/7.0.x branch exactly the same - it uses the current version number, so the two branches don't override each other

PMD's own documentation is now additionally deployed to https://docs.pmd-code.org/pmd-doc-VERSION/ . On snapshot builds, a symlink is updated, so that https://docs.pmd-code.org/snapshot/ always points to the latest snapshot. Note: This is only done on branch master, so pmd/7.0.x has no symlink.

On a release, the symlink "latest" is created and the old snaphot doc is deleted.

The javadoc linking between modules is solved manually using a relative url. This means, it should work also on javadoc.io (I'm using the same folder hierarchy). Only the linking to the core modules (pmd-core, pmd-test, pmd-lang-test) is enabled. E.g. there should never be a dependency from pmd-core -> pmd-java. But the other way round is valid and the correct linking is generated.

The javadocs of all modules are uploaded and extracted to https://docs.pmd-code.org/apidocs/ . The javadoc_tag uses now this base URL for javadoc links. Now that we have snapshot javadocs, the links in the release notes work now before a release: https://docs.pmd-code.org/snapshot/pmd_release_notes.html

On a release, the snapshot versions of the javadocs are removed.

Open Points:

• Not sure, why sub-packages of a internal package are not excluded -> https://docs.pmd-code.org/apidocs/pmd-core/6.23.0-SNAPSHOT/net/sourceforge/pmd/internal/util/package-summary.html . But shouldn't we rename this package into net.sourceforge.pmd.util.internal?
• Not sure, whether the linking to pmd-lang-test really works. Dokka still can't create proper javadoc (see Fail to generate Javadoc with Java 10 (Doclet missing?) Kotlin/dokka#294), but for now, I think, we can't have something better than this: https://docs.pmd-code.org/apidocs/pmd-lang-test/6.23.0-SNAPSHOT/
• Could we also exclude the packages under lang.*.rule.*? IMO the rule implementations should be internal, their Javadoc is irrelevant (from [doc] Generate docs for PMD 7 #1769 (comment))
  • Agreed, that we should be careful with exposing rule implementations. But rather than excluding this package, wouldn't it make sense to move the rule impls into "internal"?
• Both modules pmd-test and pmd-core have the package net.sourceforge.pmd.lang. That's why the order of the offline links provided to javadoc matters... javadoc only looks at the package list and takes the last offline link, that matches. If the order is swapped, then e.g. the link on https://docs.pmd-code.org/apidocs/pmd-java/6.23.0-SNAPSHOT/net/sourceforge/pmd/lang/java/JavaLanguageHandler.html to AbstractLanguageVersionHandler would point to pmd-test, where the class is not found. For PMD 7, we should clean this up.
• I didn't restrict the scripts to run on specific branches only. This means e.g. the java-grammar branch overrides the artifacts of pmd/7.0.x (like it already does). However, this should not be a problem, since java-grammer and pmd/7.0.x are kept up to date regularly (thanks Clément!).
• I didn't change pmd.github.io yet. We might change the urls for the doc to point to docs.pmd-code.org - although I'm not sure about the implications for googles search index...