remove `Context` boiler plate from build files

[cvogt]

In order to remove noise from build files we could have Context be concrete, but undefined on the BasicBuild and then inject it later

class BasicBuild{
  def context: Context = throw new Exception("Context is injected by CBT via refinement")
}

A concrete build.scala would then simply look like this:

class Build extends BasicBuild{ ... }

instead of this

class Build(context: Context) extends BasicBuild(context){ ... }

cbt would have another source file that it would compile together with the user provided source files for every build:

class BuildWithContext(override val context: Context) extends Build

cbt would then instantiate BuildWithContext instead of Buildas it is now.

We could also make Build a trait, but this would obfuscate compile errors in case of unimplemented abstract members. They would show as missing in BuildWithContext instead of missing inBuild where they make more sense for the user.

(cc @densh)

[nafg]

Why not make it abstract?

[cvogt]

@nafg same problem like trait. If the parent class requires implementing a field that the user forgets, the error message the users sees would be something like class BuildWithContext in file /path/to/cbt/with_context/BuildWithContext.scala:3 does not implement required member foo. More helpful would be class /path/to/user/build/build.scala:3 does not implement required member foo.

[cvogt]

I am actually happy with the current state
class Build(val context: Context) extends BaseBuild
@nafg supports trying again to switch to traits
trait Build extends BaseBuild
to reduce boiler plate

Seems harder to implement at the moment. Putting this into the backlog unless somebody steps up. If nobody does, we may want to close this eventually.

[cvogt]

@densh scheduled allowing trait Build instead of class Build(val: context: Context) this milestone 1.0 :) cc @nafg

[densh]

@cvogt Looking forward to it!