Cleanup coverage instrumentation

Author: TheElectronWill

NOTICE.md

@@ -88,6 +88,10 @@ major authors were omitted by oversight.
     docs/js/. Please refer to the license header of the concerned files for
     details.
 
+  * dotty.tools.dotc.coverage: Coverage instrumentation utilities have been
+    adapted from the scoverage plugin for scala 2 [5], which is under the
+    Apache 2.0 license.
+
   * The Dotty codebase contains parts which are derived from
     the ScalaPB protobuf library [4], which is under the Apache 2.0 license.
 
@@ -96,3 +100,4 @@ major authors were omitted by oversight.
 [2] https://github.com/adriaanm/scala/tree/sbt-api-consolidate/src/compiler/scala/tools/sbt
 [3] https://github.com/sbt/sbt/tree/0.13/compile/interface/src/main/scala/xsbt
 [4] https://github.com/lampepfl/dotty/pull/5783/files
+[5] https://github.com/scoverage/scalac-scoverage-plugin

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -1367,13 +1367,19 @@ object Trees {
     /** The context to use when mapping or accumulating over a tree */
     def localCtx(tree: Tree)(using Context): Context
 
+    /** The context to use when transforming a tree.
+      * It ensures that the source information is correct.
+      * TODO: ensure transform is always called with the correct context as argument
+      * @see https://github.com/lampepfl/dotty/pull/13880#discussion_r836395977
+      */
+    def transformCtx(tree: Tree)(using Context): Context =
+      if tree.source.exists && tree.source != ctx.source
+      then ctx.withSource(tree.source)
+      else ctx
+
     abstract class TreeMap(val cpy: TreeCopier = inst.cpy) { self =>
       def transform(tree: Tree)(using Context): Tree = {
-        inContext(
-          if tree.source != ctx.source && tree.source.exists
-          then ctx.withSource(tree.source)
-          else ctx
-        ){
+        inContext(transformCtx(tree)){
           Stats.record(s"TreeMap.transform/$getClass")
           if (skipTransform(tree)) tree
           else tree match {

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -116,9 +116,9 @@ trait CommonScalaSettings:
   val explainTypes: Setting[Boolean] = BooleanSetting("-explain-types", "Explain type errors in more detail (deprecated, use -explain instead).", aliases = List("--explain-types", "-explaintypes"))
   val unchecked: Setting[Boolean] = BooleanSetting("-unchecked", "Enable additional warnings where generated code depends on assumptions.", initialValue = true, aliases = List("--unchecked"))
   val language: Setting[List[String]] = MultiStringSetting("-language", "feature", "Enable one or more language features.", aliases = List("--language"))
+
   /* Coverage settings */
   val coverageOutputDir = PathSetting("-coverage-out", "Destination for coverage classfiles and instrumentation data.", "", aliases = List("--coverage-out"))
-  val coverageSourceroot = PathSetting("-coverage-sourceroot", "An alternative root dir of your sources used to relativize.", ".", aliases = List("--coverage-sourceroot"))
 
   /* Other settings */
   val encoding: Setting[String] = StringSetting("-encoding", "encoding", "Specify character encoding used by source files.", Properties.sourceEncoding, aliases = List("--encoding"))

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -461,7 +461,8 @@ class Definitions {
   }
   def NullType: TypeRef = NullClass.typeRef
 
-  @tu lazy val InvokerModuleRef = requiredModuleRef("scala.runtime.coverage.Invoker")
+  @tu lazy val InvokerModule = requiredModule("scala.runtime.coverage.Invoker")
+  @tu lazy val InvokedMethodRef = InvokerModule.requiredMethodRef("invoked")
 
   @tu lazy val ImplicitScrutineeTypeSym =
     newPermanentSymbol(ScalaPackageClass, tpnme.IMPLICITkw, EmptyFlags, TypeBounds.empty).entered

compiler/src/dotty/tools/dotc/coverage/Coverage.scala

@@ -3,13 +3,15 @@ package coverage
 
 import scala.collection.mutable
 
+/** Holds a list of statements to include in the coverage reports. */
 class Coverage:
   private val statementsById = new mutable.LongMap[Statement](256)
 
   def statements: Iterable[Statement] = statementsById.values
 
   def addStatement(stmt: Statement): Unit = statementsById(stmt.id) = stmt
 
+/** A statement that can be invoked, and thus counted as "covered" by code coverage tools. */
 case class Statement(
     source: String,
     location: Location,
@@ -24,6 +26,7 @@ case class Statement(
     var count: Int = 0,
     ignored: Boolean = false
 ):
+  /** Records that this statement has been invoked one more time. */
   def invoked(): Unit =
     count += 1
 

compiler/src/dotty/tools/dotc/coverage/Location.scala

@@ -4,24 +4,28 @@ package coverage
 import ast.tpd._
 import dotty.tools.dotc.core.Contexts.Context
 import dotty.tools.dotc.core.Flags.*
+import java.nio.file.Path
 
-/** @param packageName
-  *   the name of the encosing package
-  * @param className
-  *   the name of the closes enclosing class
-  * @param fullClassName
-  *   the fully qualified name of the closest enclosing class
+/** Information about the location of a coverable piece of code.
+  *
+  * @param packageName    name of the enclosing package
+  * @param className      name of the closest enclosing class
+  * @param fullClassName  fully qualified name of the closest enclosing class
+  * @param classType      "type" of the closest enclosing class: Class, Trait or Object
+  * @param method name    of the closest enclosing method
+  * @param sourcePath     absolute path of the source file
   */
 final case class Location(
     packageName: String,
     className: String,
     fullClassName: String,
     classType: String,
     method: String,
-    sourcePath: String
+    sourcePath: Path
 )
 
 object Location:
+  /** Extracts the location info of a Tree. */
   def apply(tree: Tree)(using ctx: Context): Location =
 
     val enclosingClass = ctx.owner.denot.enclosingClass
@@ -39,5 +43,5 @@ object Location:
       s"$packageName.$className",
       classType,
       ctx.owner.denot.enclosingMethod.name.toSimpleName.toString(),
-      ctx.source.file.absolute.toString()
+      ctx.source.file.absolute.jpath
     )

compiler/src/dotty/tools/dotc/coverage/Serializer.scala

@@ -30,8 +30,8 @@ object Serializer:
    */
   def serialize(coverage: Coverage, writer: Writer, sourceRoot: Path): Unit =
 
-    def getRelativePath(filePath: String): String =
-      val relPath = sourceRoot.relativize(Paths.get(filePath).toAbsolutePath)
+    def getRelativePath(filePath: Path): String =
+      val relPath = sourceRoot.relativize(filePath)
       relPath.toString
 
     def writeHeader(writer: Writer): Unit =