Implement @static sip.

This pull request implements most of machinery needed for
scala/docs.scala-lang#491

Only 3-rd check is not implemented by this commit.
I propose to get this in faster to fix scala#1149

Author: DarkDimius

src/dotty/tools/backend/jvm/DottyBackendInterface.scala

@@ -601,7 +601,8 @@ class DottyBackendInterface(outputDirectory: AbstractFile)(implicit ctx: Context
       isPrivate //|| (sym.isPrimaryConstructor && sym.owner.isTopLevelModuleClass)
 
     def isFinal: Boolean = sym is Flags.Final
-    def isStaticMember: Boolean = (sym ne NoSymbol) && ((sym is Flags.JavaStatic) || (owner is Flags.ImplClass))
+    def isStaticMember: Boolean = (sym ne NoSymbol) &&
+      ((sym is Flags.JavaStatic) || (owner is Flags.ImplClass) || toDenot(sym).hasAnnotation(ctx.definitions.ScalaStaticAnnot))
       // guard against no sumbol cause this code is executed to select which call type(static\dynamic) to use to call array.clone
 
     def isBottomClass: Boolean = (sym ne defn.NullClass) && (sym ne defn.NothingClass)

src/dotty/tools/dotc/Compiler.scala

@@ -44,6 +44,7 @@ class Compiler {
       List(new FirstTransform,
            new CheckReentrant),
       List(new RefChecks,
+           new CheckStatic,
            new ElimRepeated,
            new NormalizeFlags,
            new ExtensionMethods,

src/dotty/tools/dotc/ast/tpd.scala

@@ -320,7 +320,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
       case _ =>
         false
     }
-    try test || tp.symbol.is(JavaStatic)
+    try test || tp.symbol.is(JavaStatic) || tp.symbol.hasAnnotation(defn.ScalaStaticAnnot)
     catch { // See remark in SymDenotations#accessWithin
       case ex: NotDefinedHere => test(ctx.addMode(Mode.FutureDefsOK))
     }
@@ -337,6 +337,8 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
     else if (prefixIsElidable(tp)) Ident(tp)
     else if (tp.symbol.is(Module) && ctx.owner.isContainedIn(tp.symbol.moduleClass))
       followOuterLinks(This(tp.symbol.moduleClass.asClass))
+    else if (tp.symbol hasAnnotation defn.ScalaStaticAnnot)
+         Ident(tp)
     else tp.prefix match {
       case pre: SingletonType => followOuterLinks(singleton(pre)).select(tp)
       case pre => SelectFromTypeTree(TypeTree(pre), tp)

src/dotty/tools/dotc/core/Definitions.scala

@@ -462,6 +462,8 @@ class Definitions {
   def ScalaLongSignatureAnnot(implicit ctx: Context) = ScalaLongSignatureAnnotType.symbol.asClass
   lazy val ScalaStrictFPAnnotType            = ctx.requiredClassRef("scala.annotation.strictfp")
   def ScalaStrictFPAnnot(implicit ctx: Context) = ScalaStrictFPAnnotType.symbol.asClass
+  lazy val ScalaStaticAnnotType            = ctx.requiredClassRef("scala.annotation.static")
+  def ScalaStaticAnnot(implicit ctx: Context) = ScalaStaticAnnotType.symbol.asClass
   lazy val SerialVersionUIDAnnotType         = ctx.requiredClassRef("scala.SerialVersionUID")
   def SerialVersionUIDAnnot(implicit ctx: Context) = SerialVersionUIDAnnotType.symbol.asClass
   lazy val TASTYSignatureAnnotType = ctx.requiredClassRef("scala.annotation.internal.TASTYSignature")

src/dotty/tools/dotc/core/SymDenotations.scala

@@ -285,6 +285,10 @@ object SymDenotations {
     final def addAnnotation(annot: Annotation): Unit =
       annotations = annot :: myAnnotations
 
+    /** Add given annotation to the annotations of this denotation */
+    final def addAnnotation(annot: ClassSymbol)(implicit ctx: Context): Unit =
+      addAnnotation(ConcreteAnnotation(tpd.ref(annot)))
+
     /** Remove annotation with given class from this denotation */
     final def removeAnnotation(cls: Symbol)(implicit ctx: Context): Unit =
       annotations = myAnnotations.filterNot(_ matches cls)

src/scala/annotation/static.scala

@@ -0,0 +1,13 @@
+package scala.annotation
+
+import scala.annotation.meta._
+
+/** https://github.com/scala/scala.github.com/pull/491 */
+
+@field
+@getter
+@beanGetter
+@beanGetter
+@param
+@setter
+final class static extends StaticAnnotation