The gradle build is currently missing or could use some love in the following areas:

- Apply forbiddenAPIs

- configure security policy/ sandboxing for tests (!).

- add test 'beasting' (rerunning the same suite multiple times). I'm afraid it'll be difficult
  to run it sensibly because gradle doesn't offer cwd separation for the forked test runners (?)

- jar checksums, jar checksum computation and validation.
  this should be done without intermediate folders (directly
  on dependency sets).

- add a :helpDeps explanation to how the dependency system works (palantir plugin, lockfile) and
  how to retrieve structured information about current dependencies of a given module 
  (in a tree-like output).

- identify and list precommit tasks so that they can be ported one by one.

- identify and port any other "check" utilities that may be called from ant.

- identify and port various "regenerate" tasks from ant builds (javacc, precompiled automata, etc.)

- add rendering of javadocs (gradlew javadoc) and attaching them to maven publications.

- fill in POM details in gradle/defaults-maven.gradle so that they reflect the previous content better
  (dependencies aside).

- Add any IDE integration layers that should be added (I use IntelliJ and it imports the project
  out of the box, without the need for any special tuning).

- Clean up dependencies, especially for Solr: any { transitive = false } should just explicitly
  exclude whatever they don't need (and their dependencies currently declared explicitly
  should be folded). Figure out which scope to import a dependency to.

- add Solr packaging for docs/* (see TODO in packaging/build.gradle; currently XSLT...)

- I didn't bother adding Solr dist/test-framework to packaging (who'd use it from a binary
  distribution?)

Intentional differences:

- the back-compatibility target 'resolve' is added to gradle but it's really for informational purposes
  and debugging. Packaging should be done from subcomponent configurations and dependencies,
  not from source folders... "gradlew -p packaging assemble" puts together the entire Solr distribution
  under packaging/build where it doesn't interfere with sources.

  'resolve' for Lucene  also does *not* copy test dependencies under lib/ (like ant version does).

- transitive export of certain core libraries from solr-core/ solrj (guava, etc.).