Add note detailing possible memory leak in StoreReporter

Author: felixmulder

src/dotty/tools/dotc/reporting/StoreReporter.scala

@@ -8,9 +8,16 @@ import config.Printers.typr
 import diagnostic.MessageContainer
 import diagnostic.messages._
 
-/**
- * This class implements a Reporter that stores all messages
- */
+/** This class implements a Reporter that stores all messages
+  *
+  * Beware that this reporter can leak memory, and force messages in two
+  * scenarios:
+  *
+  * - During debugging `config.Printers.typr` is set from `noPrinter` to `new
+  *   Printer`, which forces the message
+  * - The reporter is not flushed and the message containers capture a
+  *   `Context` (about 4MB)
+  */
 class StoreReporter(outer: Reporter) extends Reporter {
 
   private var infos: mutable.ListBuffer[MessageContainer] = null