Recognize java enums as constants from source.

Fixed up one of the mismatches between how java source is modeled
and how java bytecode is modeled.  We should get the rest of them
too.  Closes SI-2764.

src/compiler/scala/reflect/internal/StdNames.scala

@@ -766,7 +766,6 @@ trait StdNames {
   object fulltpnme extends TypeNames {
     val RuntimeNothing: NameType = "scala.runtime.Nothing$"
     val RuntimeNull: NameType    = "scala.runtime.Null$"
-    val JavaLangEnum: NameType   = "java.lang.Enum"
   }
 
   /** Java binary names, like scala/runtime/Nothing$.

src/compiler/scala/tools/nsc/javac/JavaParsers.scala

@@ -872,7 +872,10 @@ trait JavaParsers extends ast.parser.ParsersCommon with JavaScanners {
           skipAhead()
           accept(RBRACE)
         }
-        ValDef(Modifiers(Flags.JAVA | Flags.STATIC), name, enumType, blankExpr)
+        // The STABLE flag is to signal to namer that this was read from a
+        // java enum, and so should be given a Constant type (thereby making
+        // it usable in annotations.)
+        ValDef(Modifiers(Flags.STABLE | Flags.JAVA | Flags.STATIC), name, enumType, blankExpr)
       }
     }
 

src/compiler/scala/tools/nsc/typechecker/Namers.scala

@@ -567,7 +567,15 @@ trait Namers extends MethodSynthesis {
         assignAndEnterFinishedSymbol(tree)
       else
         enterGetterSetter(tree)
+
+      // When java enums are read from bytecode, they are known to have
+      // constant types by the jvm flag and assigned accordingly.  When
+      // they are read from source, the java parser marks them with the
+      // STABLE flag, and now we receive that signal.
+      if (tree.symbol hasAllFlags STABLE | JAVA)
+        tree.symbol setInfo ConstantType(Constant(tree.symbol))
     }
+
     def enterLazyVal(tree: ValDef, lazyAccessor: Symbol): TermSymbol = {
       // If the owner is not a class, this is a lazy val from a method,
       // with no associated field.  It has an accessor with $lzy appended to its name and

test/files/pos/t2764/Ann.java

@@ -0,0 +1,5 @@
+package bippy;
+
+public @interface Ann {
+  Enum value();
+}

test/files/pos/t2764/Enum.java

@@ -0,0 +1,5 @@
+package bippy;
+
+public enum Enum {
+  VALUE;
+}

test/files/pos/t2764/Use.scala

@@ -0,0 +1,6 @@
+package bippy
+
+class Use {
+  @Ann(Enum.VALUE)
+  def foo {}
+}