Warn about scala binary version suffix on dependencies

The @@dependency directive renders sbt/Maven/Gradle/… snippets to easily copy paste a library dependency on the users build code.

The dependencies usually include a scala.binary.version suffix which can lead users unfamiliar with the scala ecosystem to mixing artifacts such as akka-actor_2.13 and akka-testkit_2.12 which leads to obscure errors (e.g. noclassdeffounderror scala/serializable).

The @@dependency could, instead, not set the scala.binary.version to a given value and use a build-specific placeholder (e.g. Maven property) with a small comment similar to the support to symbol/value in:

@@dependency [Maven,sbt,Gradle] {
  group=com.typesafe.akka
  artifact=akka-stream-kafka-testkit_$scala.binary.version$
  version=$project.version$
  scope=test
  symbol2=AkkaVersion
  value2="$akka.version$"
  group2=com.typesafe.akka
  artifact2=akka-stream-testkit_$scala.binary.version$
  version2=AkkaVersion
  scope2=test
}

rendering as

    <properties>
      <akka.version>2.5.23</akka.version>
    </properties>
    <dependency>
      <groupId>com.typesafe.akka</groupId>
      <artifactId>akka-stream-kafka-testkit_2.12</artifactId>
      <version>2.0.2</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>com.typesafe.akka</groupId>
      <artifactId>akka-stream-testkit_2.12</artifactId>
      <version>${akka.version}</version>
      <scope>test</scope>
    </dependency>

But such that any paradox user gets the symbol/value usage out fo the box (instead fo copy/pasting it every single time).

This came up during a gitter discussion.

So, a paradox user simply adding:

@@dependency [Maven,sbt,Gradle] {
  group=com.typesafe.akka
  artifact=akka-stream-kafka-testkit_$scala.binary.version$
  version=$project.version$
  scope=test
}

would get the following maven snippet for free:

    <properties>
      <scala.binary.version>2.5.23</scala.binary.version>
    </properties>
    <dependency>
      <groupId>com.typesafe.akka</groupId>
      <artifactId>akka-stream-kafka-testkit_${scala.binary.version}</artifactId>
      <version>2.0.2</version>
      <scope>test</scope>
    </dependency>

Optionally with a comment:

    <properties>
      <!-- All your artifacts must be compiled to the same scala.binary.version  (TODO: adda  link here to some relevant documentation in scala-lang.org ?)-->
      <scala.binary.version>2.5.23</scala.binary.version>
    </properties>

[ennru]

I looked into this. My plan would be to enable this automatically as soon as an artefact name uses $scala.binary.version$.

[ennru]

Implemented with #429