build.sbt

scalaVersion := "2.12.4"

libraryDependencies += "org.scala-lang" % "scala-reflect" % scalaVersion.value

log

force_true > test:run
[info] Updating ...
[info] Done updating.
[info] Compiling 1 Scala source to /Users/kenji_yoshida/force_true/target/scala-2.12/classes ...
[info] Done compiling.
[info] Compiling 1 Scala source to /Users/kenji_yoshida/force_true/target/scala-2.12/test-classes ...
[info] Packaging /Users/kenji_yoshida/force_true/target/scala-2.12/force_true_2.12-0.1.0-SNAPSHOT.jar ...
[info] Done packaging.
 a.==(1) を強制的に true に変換します（ ＾ω＾）
 a.==(2) を強制的に true に変換します（ ＾ω＾）
 a.==(3) を強制的に true に変換します（ ＾ω＾）
[info] Done compiling.
[info] Packaging /Users/kenji_yoshida/force_true/target/scala-2.12/force_true_2.12-0.1.0-SNAPSHOT-tests.jar ...
[info] Done packaging.
[info] Running example.Test 
true
[success] Total time: 2 s, completed 2018/01/24 14:07:14

Main.scala

// src/main/scala/Main.scala

package example

import scala.reflect.macros.blackbox.Context
import scala.language.experimental.macros

object Main {
  def foo[A](f: A): A = macro Main.fooImpl[A]

  def fooImpl[A: c.WeakTypeTag](c: reflect.macros.blackbox.Context)(f: c.Tree) = {
    import c.universe._

    val transformer = new Transformer{
      override def transform(tree: Tree) = super.transform{
        tree match {
          case q"${x} == ${y}" =>
            println(s" $tree を強制的に true に変換します（ ＾ω＾）")
            c.typecheck(q"true")
          case _ =>
            tree
        }
      }
    }

    transformer.transform(f)
  }
}

Test.scala

// src/test/scala/Test.scala

package example

object Test {
  def main(args: Array[String]): Unit = Main.foo{
    val a = 0
    val result = (a == 1) && (a == 2) && (a == 3)
    println(result)
  }
}