Evaluate annotations in Namer

Annotations were evaluated in Typer, which meant that they could be used only after type checking was
complete (or compilation order dependencies would be introduced). This commit makes annotations be
installed as part of completion in Namer. However, annotations are now lazy so as to avoid cyclic
references. This is completely analogous to the scheme in unpickler and ClassfileParser.

Author: odersky

src/dotty/tools/dotc/typer/Namer.scala

@@ -15,6 +15,7 @@ import annotation.tailrec
 import ErrorReporting._
 import tpd.ListOfTreeDecorator
 import config.Printers._
+import Annotations._
 import language.implicitConversions
 
 trait NamerContextOps { this: Context =>
@@ -495,8 +496,23 @@ class Namer { typer: Typer =>
       completeInCreationContext(denot)
     }
 
-    def completeInCreationContext(denot: SymDenotation): Unit =
+    protected def addAnnotations(denot: SymDenotation): Unit = original match {
+      case original: untpd.MemberDef =>
+        for (annotTree <- untpd.modsDeco(original).mods.annotations) {
+          val cls = typedAheadAnnotation(annotTree)
+          val ann = Annotation.deferred(cls, implicit ctx => typedAnnotation(annotTree))
+          denot.addAnnotation(ann)
+        }
+      case _ =>
+    }
+
+    /** Intentionally left without `implicit ctx` parameter. We need
+     *  to pick up the context at the point where the completer was created.
+     */
+    def completeInCreationContext(denot: SymDenotation): Unit = {
       denot.info = typeSig(denot.symbol)
+      addAnnotations(denot)
+    }
   }
 
   class ClassCompleter(cls: ClassSymbol, original: TypeDef)(ictx: Context) extends Completer(original)(ictx) {
@@ -563,6 +579,7 @@ class Namer { typer: Typer =>
 
       index(rest)(inClassContext(selfInfo))
       denot.info = ClassInfo(cls.owner.thisType, cls, parentRefs, decls, selfInfo)
+      addAnnotations(denot)
       if (impl.body forall isNoInitMember) cls.setFlag(NoInits)
     }
   }
@@ -585,6 +602,13 @@ class Namer { typer: Typer =>
   def typedAheadExpr(tree: Tree, pt: Type = WildcardType)(implicit ctx: Context): tpd.Tree =
     typedAheadImpl(tree, pt)(ctx retractMode Mode.PatternOrType)
 
+  def typedAheadAnnotation(tree: Tree)(implicit ctx: Context): Symbol = tree match {
+    case Apply(fn, _) => typedAheadAnnotation(fn)
+    case TypeApply(fn, _) => typedAheadAnnotation(fn)
+    case Select(qual, nme.CONSTRUCTOR) => typedAheadAnnotation(qual)
+    case New(tpt) => typedAheadType(tpt).tpe.classSymbol
+  }
+
   /** Enter and typecheck parameter list */
   def completeParams(params: List[MemberDef])(implicit ctx: Context) = {
     index(params)

src/dotty/tools/dotc/typer/Typer.scala

@@ -863,7 +863,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
 
   def addTypedModifiersAnnotations(mdef: untpd.MemberDef, sym: Symbol)(implicit ctx: Context): Unit = {
     val mods1 = typedModifiers(untpd.modsDeco(mdef).mods, sym)
-    for (tree <- mods1.annotations) sym.addAnnotation(Annotation(tree))
+    sym.annotations.foreach(_.tree) // force trees to be computed
   }
 
   def typedModifiers(mods: untpd.Modifiers, sym: Symbol)(implicit ctx: Context): Modifiers = track("typedModifiers") {