1 files changed, 96 insertions, 0 deletions
diff --git a/src/compiler/scala/tools/nsc/typechecker/StdAttachments.scala b/src/compiler/scala/tools/nsc/typechecker/StdAttachments.scala
index 20db479463..64fcda3b80 100644
--- a/src/compiler/scala/tools/nsc/typechecker/StdAttachments.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/StdAttachments.scala
@@ -14,6 +14,102 @@ trait StdAttachments {
   type MacroContext = UnaffiliatedMacroContext { val universe: self.global.type }
   case class MacroRuntimeAttachment(delayed: Boolean, typerContext: Context, macroContext: Option[MacroContext])
 
+  /** Scratchpad for the macro expander, which is used to store all intermediate data except the details about the runtime.
+   */
+  case class MacroExpanderAttachment(original: Tree, desugared: Tree, role: MacroRole)
+
+  /** Loads underlying MacroExpanderAttachment from a macro expandee or returns a default value for that attachment.
+   */
+ def macroExpanderAttachment(tree: Tree): MacroExpanderAttachment =
+    tree.attachments.get[MacroExpanderAttachment] getOrElse {
+      tree match {
+        case Apply(fn, _) if tree.isInstanceOf[ApplyToImplicitArgs] => macroExpanderAttachment(fn)
+        case _ => MacroExpanderAttachment(tree, EmptyTree, APPLY_ROLE)
+      }
+    }
+
+  /** After macro expansion is completed, links the expandee and the expansion result
+   *  by annotating them both with a `MacroExpansionAttachment`.
+   */
+  def linkExpandeeAndDesugared(expandee: Tree, desugared: Tree, role: MacroRole): Unit = {
+    val metadata = MacroExpanderAttachment(expandee, desugared, role)
+    expandee updateAttachment metadata
+    desugared updateAttachment metadata
+  }
+
+  /** Is added by the macro engine to originals and results of macro expansions.
+   *  Stores the original expandee as it entered the `macroExpand` function.
+   */
+  case class MacroExpansionAttachment(expandee: Tree, expanded: Any)
+
+  /** Determines whether the target is either an original or a result of a macro expansion.
+   *  The parameter is of type `Any`, because macros can expand both into trees and into annotations.
+   */
+  def hasMacroExpansionAttachment(any: Any): Boolean = any match {
+    case tree: Tree => tree.attachments.get[MacroExpansionAttachment].isDefined
+    case _ => false
+  }
+
+  /** After macro expansion is completed, links the expandee and the expansion result by annotating them both with a `MacroExpansionAttachment`.
+   *  The `expanded` parameter is of type `Any`, because macros can expand both into trees and into annotations.
+   */
+  def linkExpandeeAndExpanded(expandee: Tree, expanded: Any): Unit = {
+    val metadata = MacroExpansionAttachment(expandee, expanded)
+    expandee updateAttachment metadata
+    expanded match {
+      case expanded: Tree => expanded updateAttachment metadata
+      case _ => // do nothing
+    }
+  }
+
+  /** Checks whether there is any tree resulting from a macro expansion and associated with the current tree.
+   */
+  object ExpandedIntoTree {
+    def unapply(tree: Tree): Option[Tree] = tree.attachments.get[MacroExpansionAttachment] match {
+      case Some(MacroExpansionAttachment(_, tree: Tree)) => Some(tree)
+      case _ => None
+    }
+  }
+
+  /** When present, suppresses macro expansion for the host.
+   *  This is occasionally necessary, e.g. to prohibit eta-expansion of macros.
+   *
+   *  Does not affect expandability of child nodes, there's context.withMacrosDisabled for that
+   *  (but think thrice before using that API - see the discussion at https://github.com/scala/scala/pull/1639).
+   */
+  case object SuppressMacroExpansionAttachment
+
+  /** Suppresses macro expansion of the tree by putting SuppressMacroExpansionAttachment on it.
+   */
+  def suppressMacroExpansion(tree: Tree) = tree.updateAttachment(SuppressMacroExpansionAttachment)
+
+  /** Unsuppresses macro expansion of the tree by removing SuppressMacroExpansionAttachment from it and its children.
+   */
+  def unsuppressMacroExpansion(tree: Tree): Tree = {
+    tree.removeAttachment[SuppressMacroExpansionAttachment.type]
+    tree match {
+      // see the comment to `isMacroExpansionSuppressed` to learn why we need
+      // a special traversal strategy here
+      case Apply(fn, _) => unsuppressMacroExpansion(fn)
+      case TypeApply(fn, _) => unsuppressMacroExpansion(fn)
+      case _ => // do nothing
+    }
+    tree
+  }
+
+  /** Determines whether a tree should not be expanded, because someone has put SuppressMacroExpansionAttachment on it or one of its children.
+   */
+  def isMacroExpansionSuppressed(tree: Tree): Boolean =
+    if (tree.attachments.get[SuppressMacroExpansionAttachment.type].isDefined) true
+    else tree match {
+      // we have to account for the fact that during typechecking an expandee might become wrapped,
+      // i.e. surrounded by an inferred implicit argument application or by an inferred type argument application.
+      // in that case the expandee itself will no longer be suppressed and we need to look at the core
+      case Apply(fn, _) => isMacroExpansionSuppressed(fn)
+      case TypeApply(fn, _) => isMacroExpansionSuppressed(fn)
+      case _ => false
+    }
+
   /** After being synthesized by the parser, primary constructors aren't fully baked yet.
    *  A call to super in such constructors is just a fill-me-in-later dummy resolved later
    *  by `parentTypes`. This attachment coordinates `parentTypes` and `typedTemplate` and