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project/ShadedSourceGenerator.scala

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+import sbt._
+import sbt.Keys._
+
+/**
+ * ShadedSourceGenerator - A build plugin for creating shaded versions of external dependencies
+ * 
+ * This generator downloads source JARs for specified dependencies (currently pprint, fansi, and sourcecode),
+ * extracts them, and applies patches to:
+ * 1. Add the dotty.shaded package prefix
+ * 2. Rewrite imports to use _root_ to avoid conflicts
+ * 3. Apply Scala 3 compatibility fixes (mostly due to enforcing null safety in scala/scala3)
+ * 
+ * The shaded sources are placed in the managed source directory and included in compilation.
+ * This allows the Scala 3 compiler to bundle these utilities without external dependencies.
+ */
+object ShadedSourceGenerator {
+
+  val task = Def.task {
+    val s = streams.value
+    val cacheDir = s.cacheDirectory
+    val dest = (Compile / sourceManaged).value / "downloaded"
+    val lm = dependencyResolution.value
+
+    val dependencies = Seq(
+      ("com.lihaoyi", "pprint_3", "0.9.3"),
+      ("com.lihaoyi", "fansi_3", "0.5.1"),
+      ("com.lihaoyi", "sourcecode_3", "0.4.4"),
+    )
+
+    // Create a marker file that tracks the dependencies for cache invalidation
+    val markerFile = cacheDir / "shaded-sources-marker"
+    val markerContent = dependencies.map { case (org, name, version) => s"$org:$name:$version:sources" }.mkString("\n")
+    if (!markerFile.exists || IO.read(markerFile) != markerContent) {
+      IO.write(markerFile, markerContent)
+    }
+
+    FileFunction.cached(cacheDir / "fetchShadedSources",
+      FilesInfo.lastModified, FilesInfo.exists) { _ =>
+      s.log.info(s"Downloading and processing shaded sources to $dest...")
+
+      if (dest.exists) {
+        IO.delete(dest)
+      }
+      IO.createDirectory(dest)
+
+      for((org, name, version) <- dependencies) {
+        import sbt.librarymanagement._
+
+        val moduleId = ModuleID(org, name, version).sources()
+        val retrieveDir = cacheDir / "retrieved" / s"$org-$name-$version-sources"
+
+        s.log.info(s"Retrieving $org:$name:$version:sources...")
+        val retrieved = lm.retrieve(moduleId, scalaModuleInfo = None, retrieveDir, s.log)
+        val jarFiles = retrieved.fold(
+          w => throw w.resolveException,
+          files => files.filter(_.getName.contains("-sources.jar"))
+        )
+
+        jarFiles.foreach { jarFile =>
+          s.log.info(s"Extracting ${jarFile.getName}...")
+          IO.unzip(jarFile, dest)
+        }
+      }
+
+      val scalaFiles = (dest ** "*.scala").get
+
+      // Define patches as a map from search text to replacement text
+      val patches = Map(
+        "import scala" -> "import _root_.scala",
+        " scala.collection." -> " _root_.scala.collection.",
+        "_root_.pprint" -> "_root_.dotty.shaded.pprint",
+        "_root_.fansi" -> "_root_.dotty.shaded.fansi",
+        "def apply(c: Char): Trie[T]" -> "def apply(c: Char): Trie[T] | Null",
+        "var head: Iterator[T] = null" -> "var head: Iterator[T] | Null = null",
+        "if (head != null && head.hasNext) true" -> "if (head != null && head.nn.hasNext) true",
+        "head.next()" -> "head.nn.next()",
+        "abstract class Walker" -> "@scala.annotation.nowarn abstract class Walker",
+        "object TPrintLowPri" -> "@scala.annotation.nowarn object TPrintLowPri",
+        "x.toString match{" -> "scala.runtime.ScalaRunTime.stringOf(x) match{"
+      )
+
+      val patchUsageCounter = scala.collection.mutable.Map(patches.keys.map(_ -> 0).toSeq: _*)
+
+      scalaFiles.foreach { file =>
+        val text = IO.read(file)
+        if (!file.getName.equals("CollectionName.scala")) {
+          var processedText = "package dotty.shaded\n" + text
+
+          // Apply patches and count usage
+          patches.foreach { case (search, replacement) =>
+            if (processedText.contains(search)) {
+              processedText = processedText.replace(search, replacement)
+              patchUsageCounter(search) += 1
+            }
+          }
+
+          IO.write(file, processedText)
+        }
+      }
+
+      // Assert that all patches were applied at least once
+      val unappliedPatches = patchUsageCounter.filter(_._2 == 0).keys
+      if (unappliedPatches.nonEmpty) {
+        throw new RuntimeException(s"Patches were not applied: ${unappliedPatches.mkString(", ")}")
+      }
+
+      scalaFiles.toSet
+    } (Set(markerFile)).toSeq
+
+  }
+
+}