Merge pull request scala/scala#9248 from dwijnand/2.12/conf-warnings

Author: dwijnand

library/src/scala/annotation/nowarn.scala

@@ -0,0 +1,34 @@
+/*
+ * Scala (https://www.scala-lang.org)
+ *
+ * Copyright EPFL and Lightbend, Inc.
+ *
+ * Licensed under Apache License 2.0
+ * (http://www.apache.org/licenses/LICENSE-2.0).
+ *
+ * See the NOTICE file distributed with this work for
+ * additional information regarding copyright ownership.
+ */
+
+package scala.annotation
+
+/** An annotation for local warning suppression.
+  *
+  * The optional `value` parameter allows selectively silencing messages, see `scalac -Wconf:help`
+  * for help. Examples:
+  *
+  * {{{
+  *   def f = {
+  *     1: @nowarn // don't warn "a pure expression does nothing in statement position"
+  *     2
+  *   }
+  *
+  *   @nowarn def f = { 1; deprecated() } // don't warn
+  *
+  *   @nowarn("msg=pure expression does nothing")
+  *   def f = { 1; deprecated() } // show deprecation warning
+  * }}}
+  *
+  * To ensure that a `@nowarn` annotation actually suppresses a warning, enable `-Xlint:nowarn`.
+  */
+class nowarn(value: String = "") extends ClassfileAnnotation

library/src/scala/annotation/tailrec.scala

@@ -20,4 +20,4 @@ package scala.annotation
  *
  *  @since 2.8
  */
-final class tailrec extends scala.annotation.StaticAnnotation
+final class tailrec extends StaticAnnotation

library/src/scala/annotation/unchecked/uncheckedStable.scala

@@ -12,9 +12,12 @@
 
 package scala.annotation.unchecked
 
+import scala.annotation.meta.{field, getter}
+
 /** An annotation for values that are assumed to be stable even though their
  *  types are volatile.
  *
  *  @since 2.7
  */
+@getter @field
 final class uncheckedStable extends scala.annotation.StaticAnnotation {}