scalacenter/classpath-shrinker

Scalac plugin to detect classpath entries that aren't directly used

classpath-shrinker's Issues

Macro classpath entries are flagged as unused

Hi everyone,

I am currently working on trying out the classpath-shrinker plugin with our codebase. I ran into an issue in which the plugin warns about certain used classpath entries as unused. The classpath entries warned about contain macros. If you remove the classpath entries that are flagged as unused, the code no longer compiles.

I created a repro example here: https://github.com/lucidsoftware/classpath-shrinker-example1

In this example, I have a simple source file

package foo

object Foo {
  def main(args: Array[String]): Unit = {
    import cats.implicits._
    println(true === false)
  }
}

that compiles under both Scala 2.11 and 2.12 and warns about unused classpath entries:

2.11:

james@james:~/opensource/classpath-shrinker-example1$ ./compile.sh /home/james/Desktop/scala-2.11.12/bin/scalac 2-11 macro
/home/james/Desktop/scala-2.11.12/bin/scalac -Xplugin:2-11-cp-shrinker/classpath-shrinker_2.11-0.1.1.jar -cp 2-11/cats-core_2.11-1.0.1.jar:2-11/cats-kernel_2.11-1.0.1.jar:2-11-macro/cats-macros_2.11-1.0.1.jar:2-11-macro/machinist_2.11-0.6.1.jar Foo.scala
cat: /release: No such file or directory
warning: Detected the following unused classpath entries:
/home/james/opensource/classpath-shrinker-example1/2-11-macro/cats-macros_2.11-1.0.1.jar
/home/james/opensource/classpath-shrinker-example1/2-11-macro/machinist_2.11-0.6.1.jar
one warning found

2.12:

james@james:~/opensource/classpath-shrinker-example1$ ./compile.sh /home/james/Desktop/scala-2.12.4/bin/scalac 2-12 macro
/home/james/Desktop/scala-2.12.4/bin/scalac -Xplugin:2-12-cp-shrinker/classpath-shrinker_2.12-0.1.1.jar -cp 2-12/cats-core_2.12-1.0.1.jar:2-12/cats-kernel_2.12-1.0.1.jar:2-12-macro/cats-macros_2.12-1.0.1.jar:2-12-macro/machinist_2.12-0.6.2.jar Foo.scala
warning: Detected the following unused classpath entries:
/home/james/opensource/classpath-shrinker-example1/2-12-macro/cats-macros_2.12-1.0.1.jar
/home/james/opensource/classpath-shrinker-example1/2-12-macro/machinist_2.12-0.6.2.jar
one warning found

If I remove those classpath entries, then both 2.11 and 2.12 fail to compile:

2.11:

james@james:~/opensource/classpath-shrinker-example1$ ./compile.sh /home/james/Desktop/scala-2.11.12/bin/scalac 2-11 nomacro
/home/james/Desktop/scala-2.11.12/bin/scalac -Xplugin:2-11-cp-shrinker/classpath-shrinker_2.11-0.1.1.jar -cp 2-11/cats-core_2.11-1.0.1.jar:2-11/cats-kernel_2.11-1.0.1.jar Foo.scala
cat: /release: No such file or directory
Foo.scala:6: error: macro implementation not found: $eq$eq$eq
(the most common reason for that is that you cannot use macro implementations in the same compilation run that defines them)
    println(true === false)
                 ^
one error found

2.12:

james@james:~/opensource/classpath-shrinker-example1$ ./compile.sh /home/james/Desktop/scala-2.12.4/bin/scalac 2-12 nomacro
/home/james/Desktop/scala-2.12.4/bin/scalac -Xplugin:2-12-cp-shrinker/classpath-shrinker_2.12-0.1.1.jar -cp 2-12/cats-core_2.12-1.0.1.jar:2-12/cats-kernel_2.12-1.0.1.jar Foo.scala
Foo.scala:6: error: macro implementation not found: $eq$eq$eq
(the most common reason for that is that you cannot use macro implementations in the same compilation run that defines them)
    println(true === false)
                 ^
one error found

My knowledge of the Scala compiler is not very good. I've been poking at the plugin and the Scala source without much luck. Anyone have any guidance or recommendations?

Thanks in advance for the help!