SI-2577, SI-6860: annotation type inference.

This is less than ideal:

  scala> class Bippy[T] extends annotation.StaticAnnotation
  defined class Bippy

  scala> def f: Int @Bippy = 5
  f: Int @Bippy[T]

Turns out we can infer such types. Now it says:

  scala> def f: Int @Bippy = 5
  f: Int @Bippy[Nothing]

This should put to rest many an issue with parameterized
annotations.

10 files changed, 113 insertions, 27 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index f2f8f47bf2..c12233b726 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -3458,31 +3458,28 @@ trait Typers extends Adaptations with Tags {
       }
 
       // begin typedAnnotation
-      val (fun, argss) = {
-        def extract(fun: Tree, outerArgss: List[List[Tree]]):
-          (Tree, List[List[Tree]]) = fun match {
-            case Apply(f, args) =>
-              extract(f, args :: outerArgss)
-            case Select(New(tpt), nme.CONSTRUCTOR) =>
-              (fun, outerArgss)
-            case _ =>
-              reportAnnotationError(UnexpectedTreeAnnotation(fun))
-              (setError(fun), outerArgss)
-          }
-        extract(ann, List())
-      }
+      val treeInfo.Applied(fun0, targs, argss) = treeInfo.dissectApplied(ann)
+      val typedFun0 = typed(fun0, forFunMode(mode), WildcardType)
+      val typedFunPart = (
+        // If there are dummy type arguments in typeFun part, it suggests we
+        // must type the actual constructor call, not only the select. The value
+        // arguments are how the type arguments will be inferred.
+        if (targs.isEmpty && typedFun0.exists(t => isDummyAppliedType(t.tpe)))
+          logResult(s"Retyped $typedFun0 to find type args")(typed(argss.foldLeft(fun0)(Apply(_, _))))
+        else
+          typedFun0
+      )
+      val typedFun @ Select(New(annTpt), _) = treeInfo.dissectApplied(typedFunPart).core
+      val annType = annTpt.tpe
 
-      val res = if (fun.isErroneous) ErroneousAnnotation
+      val res = if (typedFun.isErroneous) ErroneousAnnotation
       else {
-        val typedFun @ Select(New(tpt), _) = typed(fun, mode.forFunMode, WildcardType)
-        val annType = tpt.tpe
-
         if (typedFun.isErroneous) ErroneousAnnotation
         else if (annType.typeSymbol isNonBottomSubClass ClassfileAnnotationClass) {
           // annotation to be saved as java classfile annotation
           val isJava = typedFun.symbol.owner.isJavaDefined
           if (!annType.typeSymbol.isNonBottomSubClass(annClass)) {
-            reportAnnotationError(AnnotationTypeMismatchError(tpt, annClass.tpe, annType))
+            reportAnnotationError(AnnotationTypeMismatchError(annTpt, annType, annType))
           } else if (argss.length > 1) {
             reportAnnotationError(MultipleArgumentListForAnnotationError(ann))
           } else {
@@ -3534,7 +3531,7 @@ trait Typers extends Adaptations with Tags {
           val typedAnn = if (selfsym == NoSymbol) {
             // local dummy fixes SI-5544
             val localTyper = newTyper(context.make(ann, context.owner.newLocalDummy(ann.pos)))
-            localTyper.typed(ann, mode, annClass.tpe)
+            localTyper.typed(ann, mode, annType)
           }
           else {
             // Since a selfsym is supplied, the annotation should have an extra
@@ -3548,7 +3545,7 @@ trait Typers extends Adaptations with Tags {
             // sometimes does. The problem is that "self" ident's within
             // annot.constr will retain the old symbol from the previous typing.
             val func     = Function(funcparm :: Nil, ann.duplicate)
-            val funcType = appliedType(FunctionClass(1), selfsym.info, annClass.tpe_*)
+            val funcType = appliedType(FunctionClass(1), selfsym.info, annType)
             val Function(arg :: Nil, rhs) = typed(func, mode, funcType)
 
             rhs.substituteSymbols(arg.symbol :: Nil, selfsym :: Nil)
diff --git a/src/library/scala/throws.scala b/src/library/scala/throws.scala
index 159f1f02f4..5a5dd9a1f5 100644
--- a/src/library/scala/throws.scala
+++ b/src/library/scala/throws.scala
@@ -24,5 +24,5 @@ package scala
  * @since   2.1
  */
 class throws[T <: Throwable](cause: String = "") extends scala.annotation.StaticAnnotation {
-  def this(clazz: Class[T]) = this()
+  def this(clazz: Class[T]) = this("")
 }
diff --git a/src/reflect/scala/reflect/internal/AnnotationInfos.scala b/src/reflect/scala/reflect/internal/AnnotationInfos.scala
index 7a972c3f1a..70b8bd9be5 100644
--- a/src/reflect/scala/reflect/internal/AnnotationInfos.scala
+++ b/src/reflect/scala/reflect/internal/AnnotationInfos.scala
@@ -12,7 +12,7 @@ import scala.collection.immutable.ListMap
 
 /** AnnotationInfo and its helpers */
 trait AnnotationInfos extends api.Annotations { self: SymbolTable =>
-  import definitions.{ ThrowsClass, StaticAnnotationClass, isMetaAnnotation }
+  import definitions.{ ThrowsClass, ThrowableClass, StaticAnnotationClass, isMetaAnnotation }
 
   // Common annotation code between Symbol and Type.
   // For methods altering the annotation list, on Symbol it mutates
@@ -334,7 +334,7 @@ trait AnnotationInfos extends api.Annotations { self: SymbolTable =>
     * as well as “new-stye” `@throws[Exception]("cause")` annotations.
     */
   object ThrownException {
-    def unapply(ann: AnnotationInfo): Option[Symbol] =
+    def unapply(ann: AnnotationInfo): Option[Symbol] = {
       ann match {
         case AnnotationInfo(tpe, _, _) if tpe.typeSymbol != ThrowsClass =>
           None
@@ -342,8 +342,11 @@ trait AnnotationInfos extends api.Annotations { self: SymbolTable =>
         case AnnotationInfo(_, List(Literal(Constant(tpe: Type))), _) =>
           Some(tpe.typeSymbol)
         // new-style: @throws[Exception], @throws[Exception]("cause")
-        case AnnotationInfo(TypeRef(_, _, args), _, _) =>
-          Some(args.head.typeSymbol)
+        case AnnotationInfo(TypeRef(_, _, arg :: _), _, _) =>
+          Some(arg.typeSymbol)
+        case AnnotationInfo(TypeRef(_, _, Nil), _, _) =>
+          Some(ThrowableClass)
       }
+    }
   }
 }
diff --git a/src/reflect/scala/reflect/internal/TreeInfo.scala b/src/reflect/scala/reflect/internal/TreeInfo.scala
index 032a4aebef..c90e94c1c1 100644
--- a/src/reflect/scala/reflect/internal/TreeInfo.scala
+++ b/src/reflect/scala/reflect/internal/TreeInfo.scala
@@ -605,6 +605,12 @@ abstract class TreeInfo {
       }
       loop(tree)
     }
+
+    override def toString = {
+      val tstr = if (targs.isEmpty) "" else targs.mkString("[", ", ", "]")
+      val astr = argss map (args => args.mkString("(", ", ", ")")) mkString ""
+      s"$core$tstr$astr"
+    }
   }
 
   /** Returns a wrapper that knows how to destructure and analyze applications.
diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala
index b336192b67..b51028c502 100644
--- a/src/reflect/scala/reflect/internal/Types.scala
+++ b/src/reflect/scala/reflect/internal/Types.scala
@@ -2944,12 +2944,19 @@ trait Types extends api.Types { self: SymbolTable =>
     else existentialAbstraction(existentialsInType(tp), tp)
   )
 
-  def containsExistential(tpe: Type) =
-    tpe exists typeIsExistentiallyBound
+  def containsDummyTypeArg(tp: Type) = tp exists isDummyTypeArg
+  def isDummyTypeArg(tp: Type) = tp.typeSymbol.isTypeParameter
+  def isDummyAppliedType(tp: Type) = tp match {
+    case TypeRef(_, _, args) if args.nonEmpty => args exists isDummyTypeArg
+    case _                                    => false
+  }
 
   def existentialsInType(tpe: Type) =
     tpe withFilter typeIsExistentiallyBound map (_.typeSymbol)
 
+  def containsExistential(tpe: Type) =
+    tpe exists typeIsExistentiallyBound
+
   /** Precondition: params.nonEmpty.  (args.nonEmpty enforced structurally.)
    */
   class HKTypeVar(
diff --git a/test/files/pos/annotations2.scala b/test/files/pos/annotations2.scala
new file mode 100644
index 0000000000..3bce7f8ac4
--- /dev/null
+++ b/test/files/pos/annotations2.scala
@@ -0,0 +1,31 @@
+
+class B[T](x: (T, T)) {
+  def this(xx: (T, Any, Any)) = this((xx._1, xx._1))
+}
+class BAnn[T](x: (T, T)) extends scala.annotation.StaticAnnotation {
+  def this(xx: (T, Any, Any)) = this((xx._1, xx._1))
+}
+class CAnn[T](x: (T, T)) extends scala.annotation.StaticAnnotation {
+  def this(xx: Class[T]) = this((xx.newInstance(), xx.newInstance()))
+}
+
+class A1 {
+  val b1 = new B((1, 2, 3))
+  val b2 = new B((1, 2))
+  val b3 = new B[Int]((1, 2, 3))
+  val b4 = new B[Int]((1, 2))
+}
+
+class A2 {
+  @BAnn((1, 2, 3)) val b1 = null
+  @BAnn((1, 2)) val b2 = null
+  @BAnn[Int]((1, 2, 3)) val b3 = null
+  @BAnn[Int]((1, 2)) val b4 = null
+}
+
+class A3 {
+  @CAnn(classOf[Int]) val b1 = null
+  @CAnn((1, 2)) val b2 = null
+  @CAnn[Int](classOf[Int]) val b3 = null
+  @CAnn[Int]((1, 2)) val b4 = null
+}
diff --git a/test/files/run/t2577.check b/test/files/run/t2577.check
new file mode 100644
index 0000000000..4a584e4989
--- /dev/null
+++ b/test/files/run/t2577.check
@@ -0,0 +1 @@
+Nothing
diff --git a/test/files/run/t2577.scala b/test/files/run/t2577.scala
new file mode 100644
index 0000000000..6d836a3996
--- /dev/null
+++ b/test/files/run/t2577.scala
@@ -0,0 +1,17 @@
+case class annot[T]() extends scala.annotation.StaticAnnotation
+
+// type inference should infer @annot[Nothing] instead of @annot[T]
+// note the T is not in scope here!
+class Foo[@annot U]
+
+object Test {
+  import scala.reflect.runtime.universe._
+  val x = new Foo
+
+  def main(args: Array[String]): Unit = {
+    val targ = typeOf[x.type].widen match {
+      case TypeRef(_, _, arg :: _) => arg
+    }
+    println(targ)
+  }
+}
diff --git a/test/files/run/t6860.check b/test/files/run/t6860.check
new file mode 100644
index 0000000000..c96331f540
--- /dev/null
+++ b/test/files/run/t6860.check
@@ -0,0 +1,4 @@
+Bippy[String]
+Bippy[String]
+throws[Nothing]
+throws[RuntimeException]
diff --git a/test/files/run/t6860.scala b/test/files/run/t6860.scala
new file mode 100644
index 0000000000..2dcc2a67f7
--- /dev/null
+++ b/test/files/run/t6860.scala
@@ -0,0 +1,20 @@
+class Bippy[T](val value: T) extends annotation.StaticAnnotation
+
+class A {
+  @Bippy("hi") def f1: Int = 1
+  @Bippy[String]("hi") def f2: Int = 2
+
+  @throws("what do I throw?") def f3 = throw new RuntimeException
+  @throws[RuntimeException]("that's good to know!") def f4 = throw new RuntimeException
+}
+
+object Test {
+  import scala.reflect.runtime.universe._
+
+  def main(args: Array[String]): Unit = {
+    val members = typeOf[A].declarations.toList
+    val tpes = members flatMap (_.annotations) map (_.tpe)
+
+    tpes.map(_.toString).sorted foreach println
+  }
+}