fix: ignore lazy definition generated from by-name implicits

build.sbt

@@ -151,7 +151,14 @@ lazy val plugin =
       sharedSettings
     )
     .settings(
-      Test / unmanagedSourceDirectories += (Test / sourceDirectory).value / "scala-2.12+"
+      Test / unmanagedSourceDirectories += (Test / sourceDirectory).value / "scala-2.12+",
+      Test / unmanagedSourceDirectories ++= {
+        val sourceDir = (Test / sourceDirectory).value
+        CrossVersion.partialVersion(scalaVersion.value) match {
+          case Some((2, n)) if n >= 13 => Seq(sourceDir / "scala-2.13+")
+          case _                       => Seq.empty
+        }
+      }
     )
     .dependsOn(domain, reporter % "test->compile", serializer, buildInfo % Test)
 

plugin/src/main/scala/scoverage/ScoveragePlugin.scala

@@ -790,6 +790,14 @@ class ScoverageInstrumentationComponent(
           */
         case s: Select if s.symbol.isLazy => tree
 
+        // Generated by compiler for lazy definitions involving
+        // by-name implicit parameters. More on that here:
+        // https://docs.scala-lang.org/sips/byname-implicits.html
+        //
+        // final <synthetic> val lazyDefns$1: LazyDefns$1 = new LazyDefns$1();
+        // lazyDefns$1.rec$1()
+        case s: Select if s.symbol.isSynthetic => tree
+
         case s: Select =>
           instrument(
             treeCopy.Select(s, traverseApplication(s.qualifier), s.name),

plugin/src/test/scala-2.13+/scoverage/Scala213PluginCoverageTest.scala

@@ -0,0 +1,33 @@
+package scoverage
+
+import munit.FunSuite
+
+class Scala213PluginCoverageTest extends FunSuite with MacroSupport {
+
+  test(
+    "scoverage should ignore synthetic lazy definitions generated by compiler from by-name implicits"
+  ) {
+    val compiler = ScoverageCompiler.noPositionValidation
+    compiler.compileCodeSnippet(
+      """
+        |object test {
+        |
+        |  trait Foo {
+        |    def next: Foo
+        |  }
+        |
+        |  object Foo {
+        |    implicit def foo(implicit rec: => Foo): Foo =
+        |      new Foo { def next = rec }
+        |  }
+        |
+        |  val foo = implicitly[Foo]
+        |
+        |}
+        |
+      """.stripMargin
+    )
+    assert(!compiler.reporter.hasErrors)
+    assert(!compiler.reporter.hasWarnings)
+  }
+}

plugin/src/test/scala/scoverage/ScoverageCompiler.scala

@@ -57,12 +57,17 @@ private[scoverage] object ScoverageCompiler {
 
   def default: ScoverageCompiler = {
     val reporter = new scala.tools.nsc.reporters.ConsoleReporter(settings)
-    new ScoverageCompiler(settings, reporter)
+    new ScoverageCompiler(settings, reporter, validatePositions = true)
+  }
+
+  def noPositionValidation: ScoverageCompiler = {
+    val reporter = new scala.tools.nsc.reporters.ConsoleReporter(settings)
+    new ScoverageCompiler(settings, reporter, validatePositions = false)
   }
 
   def defaultJS: ScoverageCompiler = {
     val reporter = new scala.tools.nsc.reporters.ConsoleReporter(jsSettings)
-    new ScoverageCompiler(jsSettings, reporter)
+    new ScoverageCompiler(jsSettings, reporter, validatePositions = true)
   }
 
   def locationCompiler: LocationCompiler = {
@@ -152,7 +157,8 @@ private[scoverage] object ScoverageCompiler {
 
 class ScoverageCompiler(
     settings: scala.tools.nsc.Settings,
-    rep: scala.tools.nsc.reporters.Reporter
+    rep: scala.tools.nsc.reporters.Reporter,
+    validatePositions: Boolean
 ) extends scala.tools.nsc.Global(settings, rep) {
 
   def addToClassPath(file: File): Unit = {
@@ -268,7 +274,8 @@ class ScoverageCompiler(
 
   override def computeInternalPhases(): Unit = {
     super.computeInternalPhases()
-    addToPhasesSet(validator, "scoverage validator")
+    if (validatePositions)
+      addToPhasesSet(validator, "scoverage validator")
     addToPhasesSet(
       instrumentationComponent,
       "scoverage instrumentationComponent"