path: root/test/junit/scala/tools/nsc/backend/jvm/opt/UnusedLocalVariablesTest.scala

package scala.tools.nsc
package backend.jvm
package opt

import org.junit.runner.RunWith
import org.junit.runners.JUnit4
import org.junit.Test
import scala.tools.asm.Opcodes._
import org.junit.Assert._
import scala.collection.JavaConverters._

import CodeGenTools._
import scala.tools.partest.ASMConverters
import ASMConverters._
import scala.tools.testing.ClearAfterClass

@RunWith(classOf[JUnit4])
class UnusedLocalVariablesTest extends ClearAfterClass {
  val dceCompiler = cached("dceCompiler", () => newCompiler(extraArgs = "-Yopt:unreachable-code"))

  @Test
  def removeUnusedVar(): Unit = {
    val code = """def f(a: Long, b: String, c: Double): Unit = { return; var x = a; var y = x + 10 }"""
    assertLocalVarCount(code, 4) // `this, a, b, c`

    val code2 = """def f(): Unit = { var x = if (true) return else () }"""
    assertLocalVarCount(code2, 1) // x is eliminated, constant folding in scalac removes the if

    val code3 = """def f: Unit = return""" // paramless method
    assertLocalVarCount(code3, 1) // this
  }

  @Test
  def keepUsedVar(): Unit = {
    val code = """def f(a: Long, b: String, c: Double): Unit = { val x = 10 + a; val y = x + 10 }"""
    assertLocalVarCount(code, 6)

    val code2 = """def f(a: Long): Unit = { var x = if (a == 0l) return else () }"""
    assertLocalVarCount(code2, 3) // remains
  }

  @Test
  def constructorLocals(): Unit = {
    val code = """class C {
                 |  def this(a: Int) = {
                 |    this()
                 |    throw new Exception("")
                 |    val y = 0
                 |  }
                 |}
                 |""".stripMargin
    val cls = compileClasses(dceCompiler)(code).head
    val m = convertMethod(cls.methods.asScala.toList.find(_.desc == "(I)V").get)
    assertTrue(m.localVars.length == 2) // this, a, but not y


    val code2 =
      """class C {
        |  {
        |    throw new Exception("")
        |    val a = 0
        |  }
        |}
        |
        |object C {
        |  {
        |    throw new Exception("")
        |    val b = 1
        |  }
        |}
      """.stripMargin

    val clss2 = compileClasses(dceCompiler)(code2)
    val cls2 = clss2.find(_.name == "C").get
    val companion2 = clss2.find(_.name == "C$").get

    val clsConstr = convertMethod(cls2.methods.asScala.toList.find(_.name == "<init>").get)
    val companionConstr = convertMethod(companion2.methods.asScala.toList.find(_.name == "<init>").get)

    assertTrue(clsConstr.localVars.length == 1) // this
    assertTrue(companionConstr.localVars.length == 1) // this
  }

  def assertLocalVarCount(code: String, numVars: Int): Unit = {
    assertTrue(singleMethod(dceCompiler)(code).localVars.length == numVars)
  }

}