kind-projector | Compiler plugin for making type lambdas

The idiomatic way to write that would be this:

addCompilerPlugin is a shortcut for libraryDependencies += compilerPlugin(dependency)

Thus, it should work with something like this

I am pretty sure they are the same.

From Overriding the publishing convention:

crossVersion setting can override the publishing convention:

• CrossVersion.disabled (no suffix)
• CrossVersion.binary (_)
• CrossVersion.full (_)

The default is either CrossVersion.binary or CrossVersion.diabled depending on the value of crossPaths.

From More about using cross-built libraries:

These are equivalent:

Remeber sbt is recursive.

.sbt define things that are available in the current layer.
.scala files define thins that will be available in the next layer.

Adding an sbt plugin in project/bar.sbt is adding that plugin to the meta layer, as such the meta-layer that compiles the sbt you are using to compile your project adds those plugins to the next sbt layer.

So if you add a compiler plugin in project/foo.sbt then you are adding that compiler plugin to the compiler used to compile the project (meta) layer of sbt, but it will not be available in the current layer of sbt. That is the reason why compiler plugins are added in the build.sbt file, so they are added to the compiler used to compile your code.

Thanks to @SethTisue for answering in the comments. I am writing up a answer for anybody who might face a similar issue in the future.

As Seth mentioned, using mkTuple was the right way to go. In order to use it, you need the following import

The README.md of scala-newtype says:

This expands into a type and companion object definition, so newtypes must be defined in an object or package object.

Macros are allowed to expand classes into other classes with the same name and companion objects, but from what I can tell, the newtype annotation turns your case class into an object of the same name (along with a type alias like type DbUrl = DbUrl.Type). This behavior (turning a top-level annottee into a tree of some other kind) isn't allowed. If the annotation had generated a class DbUrl, and maybe an object of the same name, though, it would have been all right, but pretty much anything else won't work.

To fix your problem, all you need to do is move this into a package object (or some other scope, as long as it isn't top-level).

Edit: As Dmytro Mitin pointed out, the created type is not the type of DbUrl but rather something like type DbUrl = DbUrl.Type with an uppercase "T", where the definition of DbUrl.Type looks something like this (I'm just copying this from the README):

There is a bug in documentation - see https://github.com/sbt/sbt/issues/4490

Try using dedicated sbt plugin - xsbt-web-plugin - instead of reading that website. According to current docs you need to add to project/plugins.sbt

You don't have a main class, the entrypoint to your program defined. On JVM you have to have at least one class which defines