7 files changed, 129 insertions, 7 deletions
diff --git a/src/compiler/scala/reflect/internal/SymbolTable.scala b/src/compiler/scala/reflect/internal/SymbolTable.scala
index 7745b21aad..c8c1a51102 100644
--- a/src/compiler/scala/reflect/internal/SymbolTable.scala
+++ b/src/compiler/scala/reflect/internal/SymbolTable.scala
@@ -8,6 +8,7 @@ package internal
 
 import scala.collection.{ mutable, immutable }
 import util._
+import scala.tools.nsc.util.WeakHashSet
 
 abstract class SymbolTable extends api.Universe
                               with Collections
@@ -266,9 +267,10 @@ abstract class SymbolTable extends api.Universe
       }
     }
 
-    def newWeakMap[K, V]() = recordCache(mutable.WeakHashMap[K, V]())
-    def newMap[K, V]()     = recordCache(mutable.HashMap[K, V]())
-    def newSet[K]()        = recordCache(mutable.HashSet[K]())
+    def newWeakMap[K, V]()        = recordCache(mutable.WeakHashMap[K, V]())
+    def newMap[K, V]()            = recordCache(mutable.HashMap[K, V]())
+    def newSet[K]()               = recordCache(mutable.HashSet[K]())
+    def newWeakSet[K <: AnyRef]() = recordCache(new WeakHashSet[K]())
   }
 
   /** Break into repl debugger if assertion is true. */
diff --git a/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala b/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
index 2b95300bad..0e5f9ee80e 100644
--- a/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
+++ b/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
@@ -2967,9 +2967,9 @@ self =>
       val annots = annotations(true)
       val pos = in.offset
       val mods = (localModifiers() | implicitMod) withAnnotations annots
-      val defs =
+      val defs = joinComment( // for SI-5527
         if (!(mods hasFlag ~(Flags.IMPLICIT | Flags.LAZY))) defOrDcl(pos, mods)
-        else List(tmplDef(pos, mods))
+        else List(tmplDef(pos, mods)))
 
       in.token match {
         case RBRACE | CASE  => defs :+ (Literal(Constant()) setPos o2p(in.offset))
diff --git a/src/compiler/scala/tools/nsc/interactive/Global.scala b/src/compiler/scala/tools/nsc/interactive/Global.scala
index 0f28407f5a..477cec8c8e 100644
--- a/src/compiler/scala/tools/nsc/interactive/Global.scala
+++ b/src/compiler/scala/tools/nsc/interactive/Global.scala
@@ -1052,7 +1052,6 @@ class Global(settings: Settings, _reporter: Reporter, projectName: String = "")
 
   def newTyperRun() {
     currentTyperRun = new TyperRun
-    perRunCaches.clearAll()
   }
 
   class TyperResult(val tree: Tree) extends ControlThrowable
diff --git a/src/compiler/scala/tools/nsc/transform/SpecializeTypes.scala b/src/compiler/scala/tools/nsc/transform/SpecializeTypes.scala
index e5df144f2e..be6200b353 100644
--- a/src/compiler/scala/tools/nsc/transform/SpecializeTypes.scala
+++ b/src/compiler/scala/tools/nsc/transform/SpecializeTypes.scala
@@ -97,7 +97,7 @@ abstract class SpecializeTypes extends InfoTransform with TypingTransformers {
   private val wasSpecializedForTypeVars = perRunCaches.newMap[Symbol, Set[Symbol]]() withDefaultValue Set()
 
   /** Concrete methods that use a specialized type, or override such methods. */
-  private val concreteSpecMethods = perRunCaches.newSet[Symbol]()
+  private val concreteSpecMethods = perRunCaches.newWeakSet[Symbol]()
 
   private def isSpecialized(sym: Symbol)          = sym hasAnnotation SpecializedClass
   private def hasSpecializedFlag(sym: Symbol)     = sym hasFlag SPECIALIZED
diff --git a/src/compiler/scala/tools/nsc/util/WeakHashSet.scala b/src/compiler/scala/tools/nsc/util/WeakHashSet.scala
new file mode 100644
index 0000000000..6a10422b00
--- /dev/null
+++ b/src/compiler/scala/tools/nsc/util/WeakHashSet.scala
@@ -0,0 +1,60 @@
+package scala.tools.nsc.util
+
+import scala.collection.mutable
+import scala.collection.mutable.ArrayBuffer
+import scala.collection.mutable.Builder
+import scala.collection.mutable.SetBuilder
+import scala.runtime.AbstractFunction1
+
+/** A bare-bones implementation of a mutable `Set` that uses weak references
+ *  to hold the elements.
+ *
+ *  This implementation offers only add/remove/test operations,
+ *  therefore it does not fulfill the contract of Scala collection sets.
+ */
+class WeakHashSet[T <: AnyRef] extends AbstractFunction1[T, Boolean] {
+  private val underlying = mutable.HashSet[WeakReferenceWithEquals[T]]()
+
+  /** Add the given element to this set. */
+  def +=(elem: T): this.type = {
+    underlying += new WeakReferenceWithEquals(elem)
+    this
+  }
+
+  /** Remove the given element from this set. */
+  def -=(elem: T): this.type = {
+    underlying -= new WeakReferenceWithEquals(elem)
+    this
+  }
+
+  /** Does the given element belong to this set? */
+  def contains(elem: T): Boolean =
+    underlying.contains(new WeakReferenceWithEquals(elem))
+
+  /** Does the given element belong to this set? */
+  def apply(elem: T): Boolean = contains(elem)
+
+  /** Return the number of elements in this set, including reclaimed elements. */
+  def size = underlying.size
+
+  /** Remove all elements in this set. */
+  def clear() = underlying.clear()
+}
+
+/** A WeakReference implementation that implements equals and hashCode by
+ *  delegating to the referent.
+ */
+class WeakReferenceWithEquals[T <: AnyRef](ref: T) {
+  def get(): T = underlying.get()
+
+  override val hashCode = ref.hashCode
+
+  override def equals(other: Any): Boolean = other match {
+    case wf: WeakReferenceWithEquals[_] =>
+      underlying.get() == wf.get()
+    case _ =>
+      false
+  }
+
+  private val underlying = new java.lang.ref.WeakReference(ref)
+}
diff --git a/test/files/run/t5527.check b/test/files/run/t5527.check
new file mode 100644
index 0000000000..cae1a80199
--- /dev/null
+++ b/test/files/run/t5527.check
@@ -0,0 +1,20 @@
+[[syntax trees at end of parser]]// Scala source: newSource1
+package <empty> {
+  abstract trait Test extends scala.ScalaObject {
+    def $init$() = {
+      ()
+    };
+    def sth: scala.Unit = {
+      /** Some comment here */
+      object Maybe extends scala.ScalaObject {
+        def <init>() = {
+          super.<init>();
+          ()
+        };
+        /** Some comment inside */
+        def nothing() = ()
+      };
+      ()
+    }
+  }
+}
diff --git a/test/files/run/t5527.scala b/test/files/run/t5527.scala
new file mode 100644
index 0000000000..3badffde14
--- /dev/null
+++ b/test/files/run/t5527.scala
@@ -0,0 +1,41 @@
+import scala.tools.partest._
+import java.io._
+import scala.tools.nsc._
+import scala.tools.nsc.util.CommandLineParser
+import scala.tools.nsc.doc.{Settings, DocFactory}
+import scala.tools.nsc.reporters.ConsoleReporter
+
+object Test extends DirectTest {
+
+  override def extraSettings: String = "-usejavacp -Xprint:parser -Yrangepos -Ystop-after:parser -d " + testOutput.path
+
+  override def code = """
+    // SI-5527
+    trait Test {
+      def sth {
+        /** Some comment here */
+        object Maybe {
+          /** Some comment inside */
+          def nothing() = ()
+        }
+      }
+    }
+  """
+
+  override def show(): Unit = {
+    // redirect err to out, for logging
+    val prevErr = System.err
+    System.setErr(System.out)
+    compile()
+    System.setErr(prevErr)
+  }
+
+  override def newCompiler(args: String*): Global = {
+    // we want the Scaladoc compiler here, because it keeps DocDef nodes in the tree
+    val settings = new Settings(_ => ())
+    val command = new ScalaDoc.Command((CommandLineParser tokenize extraSettings) ++ args.toList, settings)
+    new DocFactory(new ConsoleReporter(settings), settings).compiler
+  }
+
+  override def isDebug = false // so we don't get the newSettings warning
+}