Compilation speed is a large pain point for many Scala developers. Twitter is one of the world’s largest Scala shops, and we continuously integrate all our projects at once in our monorepo. Lowering build times is crucial to help Twitter continue developing fast and safely. While Scala compilation is difficult to parallelize, the Language Tools team at Twitter has been working on a Scala outliner, Rsc, which produces the equivalent of C++ header files for Scala. Armed with these outlines, Scala compilation parallelism can be unlocked, allowing developers to take advantage of parallel, and even distributed, compilation to iterate ever faster. Learn how we've rolled out a Scala outliner into our continuous integration pipeline, while using open source APIs and implementations to compile and test millions of lines of code thousands of times a day to support low latency builds of Twitter's projects from source.
