adds initialize and fullyInitialize

As per Paul’s request, this commit introduces facilities to force initialization
of reflection artifacts.

Sure, initialize (actually, even fullyInitialize) is silently performed
by Symbol.typeSignature for runtime reflection, but people don’t have to
know about that.

Author: xeno-by

src/reflect/scala/reflect/api/Internals.scala

@@ -233,6 +233,23 @@ trait Internals { self: Universe =>
      */
     def deSkolemize(symbol: Symbol): Symbol
 
+    /** Forces all outstanding completers associated with this symbol.
+     *  After this call returns, the symbol becomes immutable and thread-safe.
+     */
+    def initialize(symbol: Symbol): symbol.type
+
+    /** Calls [[initialize]] on the owner and all the value and type parameters of the symbol.
+     */
+    def fullyInitialize(symbol: Symbol): symbol.type
+
+    /** Calls [[initialize]] on all the value and type parameters of the type.
+     */
+    def fullyInitialize(tp: Type): tp.type
+
+    /** Calls [[initialize]] on all the symbols that the scope consists of.
+     */
+    def fullyInitialize(scope: Scope): scope.type
+
     /** A creator for `ThisType` types.
      */
     def thisType(sym: Symbol): Type

src/reflect/scala/reflect/internal/Internals.scala

@@ -74,6 +74,10 @@ trait Internals extends api.Internals {
     def isErroneous(symbol: Symbol): Boolean = symbol.isErroneous
     def isSkolem(symbol: Symbol): Boolean = symbol.isSkolem
     def deSkolemize(symbol: Symbol): Symbol = symbol.deSkolemize
+    def initialize(symbol: Symbol): symbol.type = symbol.initialize
+    def fullyInitialize(symbol: Symbol): symbol.type = definitions.fullyInitializeSymbol(symbol).asInstanceOf[symbol.type]
+    def fullyInitialize(tp: Type): tp.type = definitions.fullyInitializeType(tp).asInstanceOf[tp.type]
+    def fullyInitialize(scope: Scope): scope.type = definitions.fullyInitializeScope(scope).asInstanceOf[scope.type]
     def attachments(symbol: Symbol): Attachments { type Pos = Position } = symbol.attachments
     def updateAttachment[T: ClassTag](symbol: Symbol, attachment: T): symbol.type = symbol.updateAttachment(attachment)
     def removeAttachment[T: ClassTag](symbol: Symbol): symbol.type = symbol.removeAttachment[T]