You use a previous version of Scala to compile the trunk version. It's turtles all the way down!
Just kidding. The initial Scala compiler was written in Java. After that was working, they rewrote it in Scala using their initial Java compiler, and then it became the process I mentioned.
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How is this managed? Is there a "backup compiler" written in some other language to compile the compiler?
You use a previous version of Scala to compile the trunk version. It's turtles all the way down!
Just kidding. The initial Scala compiler was written in Java. After that was working, they rewrote it in Scala using their initial Java compiler, and then it became the process I mentioned.