Add script to copy reference stdlib sources into stdlib-bootstrapped (#17487)

Author: dwijnand

project/Build.scala

@@ -998,6 +998,52 @@ object Build {
       // We first need to check that a project can depend on a JAR that only contains TASTy files.
       // Compile / exportJars := true,
       // Compile / packageBin / mappings ~= { _.filter(_._2.endsWith(".tasty")) },
+      run := {
+        val log = streams.value.log
+        val args: Seq[String] = spaceDelimited("<arg>").parsed
+        args.foreach(println)
+        val rootDir = (ThisBuild / baseDirectory).value
+        val srcDir = (Compile / scalaSource).value.relativeTo(rootDir).get
+        val reference = (Compile/sourceManaged).value.relativeTo(rootDir).get / "scala-library-src"
+        args match {
+          case Seq("list") =>
+            log.info(s"Printing list of non-overriden files in $reference")
+            reference.allPaths.get()
+              .flatMap(_.relativeTo(reference))
+              .filter(_.ext == "scala")
+              .sorted
+              .foreach(println)
+          case Seq(cmd @ ("clone" | "overwrite"), files*) =>
+            log.info("Cloning scala-library sources: " + files.mkString(", "))
+            for (file <- files) {
+              val referenceStdlibPaths = reference / file
+              val destination = srcDir / file
+              if (!referenceStdlibPaths.exists) {
+                log.error("Not found " + referenceStdlibPaths)
+              } else if (destination.exists && cmd == "clone") {
+                log.warn(s"Already exists $destination (use `overwrite` command to overwrite)")
+              } else {
+                val action = if (cmd == "clone") "Cloning" else "Overwriting"
+                log.info(s"$action $destination")
+                IO.copyFile(referenceStdlibPaths, destination)
+              }
+            }
+          case _ =>
+            val projectName = projectInfo.value.nameFormal
+            println(
+              s"""Usage:
+                |> $projectName/run list
+                |  -- lists all files that are not overriden in stdlib-bootstrapped/src
+                |
+                |> $projectName/run clone <sources>*
+                |  -- clones the specified sources from the stdlib-bootstrapped/src
+                |  -- example: $projectName/run clone scala/Option.scala
+                |
+                |> $projectName/run overwrite <sources>*
+                |  -- (danger) overwrites the specified sources from the stdlib-bootstrapped/src
+                |""".stripMargin)
+        }
+      }
     )
 
   /** Test the tasty generated by `stdlib-bootstrapped`