reifyAnnotations

Annotations are now supported by the reifier:
* AnnotationInfos from symbols get transformed back into mods.
* AnnotatedTypes are retained and are reified along with AnnotationInfos.

Reification is no magic, and reification of annotations especially:
* Annotations cannot refer to symbols defined inside the quasiquote.
  This restriction is due to the fact that we need to erase locally defined
  symbols before reifying to make subsequent reflective compilations succeed.
  However, while doing that, we also need to make sure that we don't make
  resulting ASTs non-compilable by removing essential information.
  This is tricky, and it more or less works for TypeTrees, but
  not for annotations that can contain arbitrary ASTs.
  For more details look into the comments to Reifiers.scala.
* Classfile annotations that contain array arguments and are applied to types,
  i.e. the ones that generate AnnotatedTypes, cannot be reified.
  This is because of limitations of manifest infrastructure.
  Typechecking "Array(mirror.LiteralAnnotArg(...))" would require the compiler
  to produce a manifest for a path-dependent type, which cannot be done now.

Review by @odersky.

1 files changed, 17 insertions, 8 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 6f6edc62c7..ef69e1525e 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -1404,7 +1404,7 @@ trait Typers extends Modes with Adaptations with PatMatVirtualiser {
     def typedClassDef(cdef: ClassDef): Tree = {
 //      attributes(cdef)
       val clazz = cdef.symbol
-      val typedMods = removeAnnotations(cdef.mods)
+      val typedMods = typedModifiers(cdef.mods)
       assert(clazz != NoSymbol, cdef)
       reenterTypeParams(cdef.tparams)
       val tparams1 = cdef.tparams mapConserve (typedTypeDef)
@@ -1441,7 +1441,7 @@ trait Typers extends Modes with Adaptations with PatMatVirtualiser {
         linkedClass.info.decl(nme.CONSTRUCTOR).alternatives foreach (_.initialize)
 
       val clazz     = mdef.symbol.moduleClass
-      val typedMods = removeAnnotations(mdef.mods)
+      val typedMods = typedModifiers(mdef.mods)
       assert(clazz != NoSymbol, mdef)
       val impl1 = typerReportAnyContextErrors(context.make(mdef.impl, clazz, newScope)) {
         _.typedTemplate(mdef.impl, {
@@ -1541,8 +1541,17 @@ trait Typers extends Modes with Adaptations with PatMatVirtualiser {
 
     /** Remove definition annotations from modifiers (they have been saved
      *  into the symbol's ``annotations'' in the type completer / namer)
+     *
+     *  However reification does need annotation definitions to proceed.
+     *  Unfortunately, AnnotationInfo doesn't provide enough info to reify it in general case.
+     *  The biggest problem is with the "atp: Type" field, which cannot be reified in some situations
+     *  that involve locally defined annotations. See more about that in Reifiers.scala.
+     *
+     *  That's why the original tree gets saved into ``original'' field of AnnotationInfo (happens elsewhere).
+     *  The field doesn't get pickled/unpickled and exists only during a single compilation run.
+     *  This simultaneously allows us to reify annotations and to preserve backward compatibility.
      */
-    def removeAnnotations(mods: Modifiers): Modifiers =
+    def typedModifiers(mods: Modifiers): Modifiers =
       mods.copy(annotations = Nil) setPositions mods.positions
 
     /**
@@ -1553,7 +1562,7 @@ trait Typers extends Modes with Adaptations with PatMatVirtualiser {
 //      attributes(vdef)
       val sym = vdef.symbol.initialize
       val typer1 = constrTyperIf(sym.isParameter && sym.owner.isConstructor)
-      val typedMods = removeAnnotations(vdef.mods)
+      val typedMods = typedModifiers(vdef.mods)
 
       // complete lazy annotations
       val annots = sym.annotations
@@ -1764,7 +1773,7 @@ trait Typers extends Modes with Adaptations with PatMatVirtualiser {
       var tpt1 = checkNoEscaping.privates(meth, typedType(ddef.tpt))
       checkNonCyclic(ddef, tpt1)
       ddef.tpt.setType(tpt1.tpe)
-      val typedMods = removeAnnotations(ddef.mods)
+      val typedMods = typedModifiers(ddef.mods)
       var rhs1 =
         if (ddef.name == nme.CONSTRUCTOR && !ddef.symbol.hasStaticFlag) { // need this to make it possible to generate static ctors
           if (!meth.isPrimaryConstructor &&
@@ -1813,7 +1822,7 @@ trait Typers extends Modes with Adaptations with PatMatVirtualiser {
       tdef.symbol.initialize
       reenterTypeParams(tdef.tparams)
       val tparams1 = tdef.tparams mapConserve typedTypeDef
-      val typedMods = removeAnnotations(tdef.mods)
+      val typedMods = typedModifiers(tdef.mods)
       // complete lazy annotations
       val annots = tdef.symbol.annotations
 
@@ -2770,7 +2779,7 @@ trait Typers extends Modes with Adaptations with PatMatVirtualiser {
             }
 
             if (hasError) annotationError
-            else AnnotationInfo(annType, List(), nvPairs map {p => (p._1, p._2.get)}).setPos(ann.pos)
+            else AnnotationInfo(annType, List(), nvPairs map {p => (p._1, p._2.get)}).setOriginal(ann).setPos(ann.pos)
           }
         } else if (requireJava) {
           reportAnnotationError(NestedAnnotationError(ann, annType))
@@ -2810,7 +2819,7 @@ trait Typers extends Modes with Adaptations with PatMatVirtualiser {
 
           def annInfo(t: Tree): AnnotationInfo = t match {
             case Apply(Select(New(tpt), nme.CONSTRUCTOR), args) =>
-              AnnotationInfo(annType, args, List()).setPos(t.pos)
+              AnnotationInfo(annType, args, List()).setOriginal(ann).setPos(t.pos)
 
             case Block(stats, expr) =>
               context.warning(t.pos, "Usage of named or default arguments transformed this annotation\n"+