scala - insert value into quasiquote - scala

Question

Unfortunately, the most intuitive way,
val world = "Earth"
val tree = q"""println("Hello $world")"""
results in
Error:(16, 36) Don't know how to unquote here
val tree = q"""println("Hello $world")"""
^
because $ within quasiquotes expects a tree.
val world = "Earth"
val tree = q"""println(${c.literal(s"Hello $world")})"""
works, but is very ugly AND I get an Intellij warning that the c.literal is deprecated and I should use quasiquotes, instead.
So ... how do I do this?
UPDATE
In response to flavian's comment:
import scala.language.experimental.macros
import scala.reflect.macros._
object TestMacros {
def doTest() = macro impl
def impl(c: blackbox.Context)(): c.Expr[Unit] = {
import c.universe._ //access to AST classes
/*
val world = "Earth"
val tree = q"""println(${c.literal(s"Hello $world")})"""
*/
val world = TermName("Earth")
val tree = q"""println("Hello $world")"""
tree match {
case q"""println("Hello Earth")""" => println("succeeded")
case _ => c.abort(c.enclosingPosition, s"huh? was: $tree")
}
c.Expr(tree) //wrap tree and tag with its type
}
}
gives
Error:(18, 40) Don't know how to unquote here
val tree = q"""println("Hello $world")"""
^

Answer 1

You need a TermName or something that's a compiler primitive.
The real problem is that you are mixing interpolators, without realising. The interpolator in hello world is really a string interpolator, not a quasiquote one which is good at unquoting trees as you suggest.
This is one way to go about it:
import c.universe._
val world = TermName("Earth")
val tree = q"""println("Hello" + ${world.decodedName.toString})"""

Answer 2

I just started learning Macro-Fu.
For those also exploring Scala 2 Macros / Scalameta Quasiquotes, seems to me the simplest approach is the following (using SBT 1.5.5; inline explanations):
scala> import scala.language.experimental.macros
| import scala.reflect.macros.blackbox
|
| object UnquoteString {
|
| def helloWorld(): Unit = macro Impl.helloWorld
|
| object Impl {
| def helloWorld(c: blackbox.Context)(): c.Expr[Unit] = {
| import c.universe._
|
| val world = "Earth" // or any other value here...
|
| val msg = s"Hello $world" // build the entire string with it here...
|
| implicitly[Liftable[String]] // as we can lift 'whole' string values with this Liftable[_]...
|
| val tree = q"""println($msg)""" // quasi-unquote the entire string here...
|
| c.Expr[Unit](Block(Nil, tree))
| }
| }
| }
import scala.language.experimental.macros
import scala.reflect.macros.blackbox
object UnquoteString
scala> UnquoteString.helloWorld()
Hello Earth
scala>
Also the following change would also work
val tree = q"""println("Hello, " + $world)""" // quasi-unquote the string to append here...