Only regenerate Scala files from GraphQL schema if schema changes

[felixbr]

In our codebase I observed that the generated files are often recompiled without explicitly cleaning them or changing the schema. This isn't a big deal for small schemas but in our case it's over 400 files that are being recompiled and takes several seconds.

I don't have a repro-case yet but it should be fairly straight forward. I can imagine using one of the test/example projects and checking how often the files are being regenerated (it should only happen if the schema changed or after an explicit clean command).

sbt already has facilities to avoid unnecessary work (e.g. used to avoid compiling files that haven't changed), so we should use that here as well imo.

References:
https://www.scala-sbt.org/1.x/docs/Caching.html
https://www.scala-sbt.org/1.x/docs/Cached-Resolution.html

[felixbr]

So, I've upgraded to 0.16.0 at work and it seems like the incremental compilation is working quite well there already.

My guess is that some of the codegen tasks where rearranged in a way that sbt understands and caches them automatically. From the docs:

sbt will automatically track the outputs of any task that returns one of the following result types: Path, Seq[Path], File or Seq[File].

https://www.scala-sbt.org/1.x/docs/Howto-Track-File-Inputs-and-Outputs.html

I'll see how it goes with the latest version and if everything's working as expected we can close this 🙂