From d0b063a0cff04ef21b6651be48b790a30fd1b681 Mon Sep 17 00:00:00 2001
From: Guillaume Martres <smarter@ubuntu.com>
Date: Tue, 14 Aug 2018 18:34:27 +0900
Subject: [PATCH] Add version-specific source directories in the library

And replace Tuple.scala with a Scala 2 implementation and a Scala 3
implementation. The Scala 2 implementaion of Tuple.scala is not strictly
necessary but could be useful if non-version-specific library sources
end up referencing scala.Tuple.
---
 .../dotty/tools/dotc/CompilationTests.scala   |  5 +++-
 library/{src => src-scala2}/scala/Tuple.scala |  6 ++---
 library/src-scala3/scala/Tuple.scala          | 26 +++++++++++++++++++
 project/Build.scala                           | 12 ++++++++-
 4 files changed, 44 insertions(+), 5 deletions(-)
 rename library/{src => src-scala2}/scala/Tuple.scala (53%)
 create mode 100644 library/src-scala3/scala/Tuple.scala

diff --git a/compiler/test/dotty/tools/dotc/CompilationTests.scala b/compiler/test/dotty/tools/dotc/CompilationTests.scala
index 74773f407a25..43f94415eaf8 100644
--- a/compiler/test/dotty/tools/dotc/CompilationTests.scala
+++ b/compiler/test/dotty/tools/dotc/CompilationTests.scala
@@ -206,8 +206,11 @@ class CompilationTests extends ParallelTesting {
       Array("-Ycheck-reentrant", "-Yemit-tasty-in-class")
     )
 
+    val libraryDirs = List(Paths.get("library/src"), Paths.get("library/src-scala3"))
+    val librarySources = libraryDirs.flatMap(d => sources(Files.walk(d)))
+
     val lib =
-      compileDir("library/src",
+      compileList("src", librarySources,
         defaultOptions.and("-Ycheck-reentrant", "-strict", "-priorityclasspath", defaultOutputDir))(libGroup)
 
     val compilerDir = Paths.get("compiler/src")
diff --git a/library/src/scala/Tuple.scala b/library/src-scala2/scala/Tuple.scala
similarity index 53%
rename from library/src/scala/Tuple.scala
rename to library/src-scala2/scala/Tuple.scala
index 1a36e841567e..febee0abd704 100644
--- a/library/src/scala/Tuple.scala
+++ b/library/src-scala2/scala/Tuple.scala
@@ -5,10 +5,10 @@ sealed trait Tuple extends Any
 
 @showAsInfix
 sealed class *:[+H, +T <: Tuple] extends Tuple {
-  @`rewrite` def head: H = ???
-  @`rewrite` def tail: T = ???
+  def head: H = ???
+  def tail: T = ???
 }
 
 object *: {
-  @`rewrite` def unapply[H, T <: Tuple](x: H *: T) = Some((x.head, x.tail))
+  def unapply[H, T <: Tuple](x: H *: T) = Some((x.head, x.tail))
 }
diff --git a/library/src-scala3/scala/Tuple.scala b/library/src-scala3/scala/Tuple.scala
new file mode 100644
index 000000000000..e53926ae4600
--- /dev/null
+++ b/library/src-scala3/scala/Tuple.scala
@@ -0,0 +1,26 @@
+package scala
+import annotation.showAsInfix
+
+object typelevel {
+  erased def erasedValue[T]: T = ???
+}
+
+import typelevel._
+
+sealed trait Tuple extends Any
+
+@showAsInfix
+sealed class *:[+H, +T <: Tuple] extends Tuple {
+  rewrite def head: H = ???
+  rewrite def tail: T = ???
+
+  rewrite private def _size(xs: Tuple): Int = //rewrite
+    xs match {
+      case _: Unit => 0
+      case _: *:[_, xs1] => _size(erasedValue[xs1]) + 1
+    }
+}
+
+object *: {
+  rewrite def unapply[H, T <: Tuple](x: H *: T) = Some((x.head, x.tail))
+}
diff --git a/project/Build.scala b/project/Build.scala
index 0b9c74474762..8cbc47480b64 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -740,7 +740,17 @@ object Build {
 
   // Settings shared between dotty-library and dotty-library-bootstrapped
   lazy val dottyLibrarySettings = Seq(
-      libraryDependencies += "org.scala-lang" % "scala-library" % scalacVersion
+    libraryDependencies += "org.scala-lang" % "scala-library" % scalacVersion,
+    // Add version-specific source directories:
+    // - files in src-scala3 will only be compiled by dotty
+    // - files in src-scala2 will only be compiled by scalac
+    unmanagedSourceDirectories in Compile += {
+      val baseDir = baseDirectory.value
+      if (isDotty.value)
+        baseDir / "src-scala3"
+      else
+        baseDir / "src-scala2"
+    }
   )
 
   lazy val `dotty-library` = project.in(file("library")).asDottyLibrary(NonBootstrapped)