Fix 196

Author: exoego

scalac-scoverage-plugin/src/main/scala/scoverage/plugin.scala

@@ -107,6 +107,14 @@ class ScoverageInstrumentationComponent(val global: Global, extraAfterPhase: Opt
   private var options: ScoverageOptions = new ScoverageOptions()
   private var coverageFilter: CoverageFilter = AllCoverageFilter
 
+  private val isScalaJsEnabled: Boolean = {
+    try {
+      rootMirror.getClassIfDefined("scala.scalajs.js.Any") != NoSymbol
+    } catch {
+      case _: Throwable => false
+    }
+  }
+
   def setOptions(options: ScoverageOptions): Unit = {
     this.options = options
     coverageFilter = new RegexCoverageFilter(options.excludedPackages, options.excludedFiles, options.excludedSymbols)
@@ -215,6 +223,10 @@ class ScoverageInstrumentationComponent(val global: Global, extraAfterPhase: Opt
           if (tree.pos.isDefined && !isStatementIncluded(tree.pos)) {
             coverage.add(statement.copy(ignored = true))
             tree
+          } else if (isUndefinedParameterInScalaJs(tree.symbol)) {
+            coverage.add(statement.copy(ignored = true))
+            statementIds.decrementAndGet()
+            tree
           } else {
             coverage.add(statement)
 
@@ -225,6 +237,11 @@ class ScoverageInstrumentationComponent(val global: Global, extraAfterPhase: Opt
       }
     }
 
+    def isUndefinedParameterInScalaJs(symbol: Symbol): Boolean = {
+      isScalaJsEnabled && symbol != null && symbol.isSynthetic && symbol.isMethod &&
+        symbol.nameString.contains("$default$") &&
+        symbol.tpe.resultType.annotations.exists(_.symbol.nameString == "uncheckedVariance")
+    }
     def isClassIncluded(symbol: Symbol): Boolean = coverageFilter.isClassIncluded(symbol.fullNameString)
     def isFileIncluded(source: SourceFile): Boolean = coverageFilter.isFileIncluded(source)
     def isStatementIncluded(pos: Position): Boolean = coverageFilter.isLineIncluded(pos)

scalac-scoverage-plugin/src/test/scala/scoverage/PluginCoverageScalaJsTest.scala

@@ -0,0 +1,25 @@
+package scoverage
+
+import org.scalatest.{ BeforeAndAfterEachTestData, FunSuite, OneInstancePerTest }
+
+/**
+ * https://github.com/scoverage/scalac-scoverage-plugin/issues/196
+ */
+class PluginCoverageScalaJsTest
+  extends FunSuite
+  with OneInstancePerTest
+  with BeforeAndAfterEachTestData
+  with MacroSupport {
+
+  test("scoverage should ignore default undefined parameter") {
+    val compiler = ScoverageCompiler.default
+    compiler.compileCodeSnippet(
+      """import scala.scalajs.js
+        |
+        |object JSONHelper {
+        |  def toJson(value: String): String = js.JSON.stringify(value)
+        |}""".stripMargin)
+    assert(!compiler.reporter.hasErrors)
+    compiler.assertNMeasuredStatements(4)
+  }
+}