From ef118b8c86944d6fe3520782335835b9ec96590a Mon Sep 17 00:00:00 2001
From: Denys Shabalin <denys.shabalin@typesafe.com>
Date: Wed, 22 Jan 2014 17:49:26 +0100
Subject: Tag synthetic unit with attachment

This makes it easy to differentiate unit inserted by a compiler vs unit
written by the user. Useful for quasiquotes and pretty printing.

Additionally SyntacticBlock extractor is changed to treat EmptyTree as
zero-element block.
---
 src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala | 4 ++--
 src/reflect/scala/reflect/internal/BuildUtils.scala         | 2 ++
 src/reflect/scala/reflect/internal/StdAttachments.scala     | 4 ++++
 src/reflect/scala/reflect/internal/TreeGen.scala            | 2 +-
 src/reflect/scala/reflect/runtime/JavaUniverseForce.scala   | 1 +
 5 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala b/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
index 87ab52414c..e0b863b749 100644
--- a/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
+++ b/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
@@ -189,8 +189,8 @@ trait Reifiers { self: Quasiquotes =>
         mirrorBuildCall(nme.SyntacticBlock, tree)
       case Block(Nil, other) =>
         reifyTree(other)
-      case Block(stats, last) =>
-        reifyBuildCall(nme.SyntacticBlock, stats :+ last)
+      case SyntacticBlock(stats) if stats.size > 1 =>
+        reifyBuildCall(nme.SyntacticBlock, stats)
       case Try(block, catches, finalizer) =>
         reifyBuildCall(nme.SyntacticTry, block, catches, finalizer)
       case Match(selector, cases) =>
diff --git a/src/reflect/scala/reflect/internal/BuildUtils.scala b/src/reflect/scala/reflect/internal/BuildUtils.scala
index 9b19dc11cb..fda8e4be5f 100644
--- a/src/reflect/scala/reflect/internal/BuildUtils.scala
+++ b/src/reflect/scala/reflect/internal/BuildUtils.scala
@@ -385,6 +385,8 @@ trait BuildUtils { self: SymbolTable =>
       def apply(stats: List[Tree]): Tree = gen.mkBlock(stats)
 
       def unapply(tree: Tree): Option[List[Tree]] = tree match {
+        case EmptyTree => Some(Nil)
+        case self.Block(stats, expr) if expr.hasAttachment[SyntheticUnitAttachment.type] => Some(stats)
         case self.Block(stats, expr) => Some(stats :+ expr)
         case _ if tree.isTerm => Some(tree :: Nil)
         case _ => None
diff --git a/src/reflect/scala/reflect/internal/StdAttachments.scala b/src/reflect/scala/reflect/internal/StdAttachments.scala
index 09fd996f39..b331bf75f6 100644
--- a/src/reflect/scala/reflect/internal/StdAttachments.scala
+++ b/src/reflect/scala/reflect/internal/StdAttachments.scala
@@ -36,6 +36,10 @@ trait StdAttachments {
    */
   case object ForAttachment extends PlainAttachment
 
+  /** Identifies unit constants which were inserted by the compiler.
+   */
+  case object SyntheticUnitAttachment extends PlainAttachment
+
   /** Untyped list of subpatterns attached to selector dummy. */
   case class SubpatternsAttachment(patterns: List[Tree])
 }
diff --git a/src/reflect/scala/reflect/internal/TreeGen.scala b/src/reflect/scala/reflect/internal/TreeGen.scala
index b16cbd8325..0e1eb7d3a9 100644
--- a/src/reflect/scala/reflect/internal/TreeGen.scala
+++ b/src/reflect/scala/reflect/internal/TreeGen.scala
@@ -447,7 +447,7 @@ abstract class TreeGen extends macros.TreeBuilder {
   /** Create block of statements `stats`  */
   def mkBlock(stats: List[Tree]): Tree =
     if (stats.isEmpty) Literal(Constant(()))
-    else if (!stats.last.isTerm) Block(stats, Literal(Constant(())))
+    else if (!stats.last.isTerm) Block(stats, Literal(Constant(())).updateAttachment(SyntheticUnitAttachment))
     else if (stats.length == 1) stats.head
     else Block(stats.init, stats.last)
 
diff --git a/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala b/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
index b9b171c7ed..8811b5513e 100644
--- a/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
+++ b/src/reflect/scala/reflect/runtime/JavaUniverseForce.scala
@@ -58,6 +58,7 @@ trait JavaUniverseForce { self: runtime.JavaUniverse  =>
     this.CompoundTypeTreeOriginalAttachment
     this.BackquotedIdentifierAttachment
     this.ForAttachment
+    this.SyntheticUnitAttachment
     this.SubpatternsAttachment
     this.noPrint
     this.typeDebug
-- 
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