Previous situation:
* The snowball base classes (Among, SnowballProgram, etc) had accumulated local performance-related changes. There was a task that would also "patch" generated classes (e.g. GermanStemmer) after-the-fact.
* Snowball classes had many "non-changes" from the original such as removal of tabs addition of javadocs, license headers, etc.
* Snowball test data (inputs and expected stems) was incorporated into lucene testing, but this was maintained manually. Also files had become large, making the test too slow (Nightly).
* Snowball stopwords lists from their website were manually maintained. In some cases encoding fixes were manually applied.
* Some generated stemmers (such as Estonian and Armenian) exist in lucene, but have no corresponding `.sbl` file in snowball sources at all.
Besides this mess, snowball project is "moving along" and acquiring new languages, adding non-BSD-licensed test data, huge test data, and other complexity. So it is time to automate the integration better.
New situation:
* Lucene has a `gradle snowball` regeneration task. It works on Linux or Mac only. It checks out their repos, applies the `snowball.patch` in our repository, compiles snowball stemmers, regenerates all java code, applies any adjustments so that our build is happy.
* Tests data is automatically regenerated from the commit hash of the snowball test data repository. Not all languages are tested from their data: only where the license is simple BSD. Test data is also (deterministically) sampled, so that we don't have huge files. We just want to make sure our integration works.
* Randomized tests are still set to test every language with generated fake words. The regeneration task ensures all languages get tested (it writes a simple text file list of them).
* Stopword files are automatically regenerated from the commit hash of the snowball website repository.
* The regeneration procedure is idempotent. This way when stuff does change, you know exactly what happened. For example if test data changes to a different license, you may see a git deletion. Or if a new language/stopwords/test data gets added, you will see git additions.
Robert Muir