1 files changed, 40 insertions, 14 deletions
diff --git a/src/dotty/tools/dotc/reporting/diagnostic/Message.scala b/src/dotty/tools/dotc/reporting/diagnostic/Message.scala
index 8b1f65673..8018a8777 100644
--- a/src/dotty/tools/dotc/reporting/diagnostic/Message.scala
+++ b/src/dotty/tools/dotc/reporting/diagnostic/Message.scala
@@ -6,6 +6,8 @@ package diagnostic
 import util.SourcePosition
 import core.Contexts.Context
 
+import messages._
+
 object Message {
   /** This implicit conversion provides a fallback for error messages that have
     * not yet been ported to the new scheme. Comment out this `implicit def` to
@@ -20,6 +22,13 @@ object Message {
   * into a `MessageContainer` which contains the log level and can later be
   * consumed by a subclass of `Reporter`.
   *
+  * NOTE: you should not be persisting messages. Most messages take an implicit
+  * `Context` and these contexts weigh in at about 4mb per instance, as such
+  * persisting these will result in a memory leak.
+  *
+  * Instead use the `persist` method to create an instance that does not keep a
+  * reference to these contexts.
+  *
   * @param errorId a unique number identifying the message, this will later be
   *                used to reference documentation online
   */
@@ -47,45 +56,62 @@ abstract class Message(val errorId: Int) { self =>
     */
   def explanation: String
 
-  /** It is possible to map `msg` to add details, this is at the loss of
-    * precision since the type of the resulting `Message` won't be original
-    * extending class
-    *
-    * @return a `Message` with the mapped message
+  /** The implicit `Context` in messages is a large thing that we don't want
+    * persisted. This method gets around that by duplicating the message
+    * without the implicit context being passed along.
     */
-  def mapMsg(f: String => String) = new Message(errorId) {
-    val msg = f(self.msg)
+  def persist: Message = new Message (errorId) {
+    val msg         = self.msg
+    val kind        = self.kind
+    val explanation = self.explanation
+  }
+}
+
+/** An extended message keeps the contained message from being evaluated, while
+  * allowing for extension for the `msg` string
+  *
+  * This is useful when we need to add additional information to an existing
+  * message.
+  */
+class ExtendMessage(_msg: () => Message)(f: String => String) { self =>
+  lazy val msg = f(_msg().msg)
+  lazy val kind = _msg().kind
+  lazy val explanation = _msg().explanation
+  lazy val errorId = _msg().errorId
+
+  private def toMessage = new Message(errorId) {
+    val msg = self.msg
     val kind = self.kind
     val explanation = self.explanation
   }
 
   /** Enclose this message in an `Error` container */
   def error(pos: SourcePosition) =
-    new Error(self, pos)
+    new Error(toMessage, pos)
 
   /** Enclose this message in an `Warning` container */
   def warning(pos: SourcePosition) =
-    new Warning(self, pos)
+    new Warning(toMessage, pos)
 
   /** Enclose this message in an `Info` container */
   def info(pos: SourcePosition) =
-    new Info(self, pos)
+    new Info(toMessage, pos)
 
   /** Enclose this message in an `FeatureWarning` container */
   def featureWarning(pos: SourcePosition) =
-    new FeatureWarning(self, pos)
+    new FeatureWarning(toMessage, pos)
 
   /** Enclose this message in an `UncheckedWarning` container */
   def uncheckedWarning(pos: SourcePosition) =
-    new UncheckedWarning(self, pos)
+    new UncheckedWarning(toMessage, pos)
 
   /** Enclose this message in an `DeprecationWarning` container */
   def deprecationWarning(pos: SourcePosition) =
-    new DeprecationWarning(self, pos)
+    new DeprecationWarning(toMessage, pos)
 
   /** Enclose this message in an `MigrationWarning` container */
   def migrationWarning(pos: SourcePosition) =
-    new MigrationWarning(self, pos)
+    new MigrationWarning(toMessage, pos)
 }
 
 /** The fallback `Message` containing no explanation and having no `kind` */