How do I generate new source code in text form in a Scala compiler plugin?

Question

I have just finished the first version of a Java 6 compiler plugin, that automatically generates wrappers (proxy, adapter, delegate, call it what you like) based on an annotatio

Answer 1

Short answer:

It can't be done

Long answer:

You could conceivably generate your source file and push that through a parser instance within your plugin. But not in any way that's likely to be of any use to you, because you'd now have a bigger problem to contend with:

In order to grab all the type/name information for generating the delagate/proxy, you'll have to pick up the annotated type's AST after it has run through both the namer and typer phases (which are inseperable). The catch is that any attempts to call your generated code will already have failed typechecking, the compiler will have thrown an error, and any further bets are off.

Method synthesis is possible in limited cases, so long as you can somehow fool the typechecker for just long enough to get your code generated, which is the trick I pulled with my Autoproxy 'lite' plugin. Even then, you're far better off working with TreeDSL to generate code instead of pumping out raw source.

Answer 2

Kevin is entirely correct, but just for completeness it's worth mentioning that there is another alternative - write a compiler plugin that generates source. This is the approach that I've adopted in Borachio. It's not a very satisfactory solution, but it can be made to work.

Edit - I just reread your question and realised that you're actually asking about generating source anyway

So there is no support for this directly, but it's basically just a question of opening a file and writing the relevant "print" statements. There's no way to invoke the compiler "inside" a plugin AFAIK, but I've written an sbt plugin which hides most of the complexity of invoking the compiler twice.