Merge pull request scala#10377 from som-snytt/deprecate/specialized

Warn about elidable under -Xsource:3

Author: lrytz

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

@@ -4015,6 +4015,8 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
         reportAnnotationError(DoesNotExtendAnnotation(typedFun, annTypeSym))
         return finish(ErroneousAnnotation)
       }
+      if (currentRun.isScala3 && (/*annTypeSym.eq(SpecializedClass) ||*/ annTypeSym.eq(ElidableMethodClass)))
+        context.deprecationWarning(ann.pos, annTypeSym, s"@${annTypeSym.fullNameString} is ignored in Scala 3", "2.13.12")
 
       /* Calling constfold right here is necessary because some trees (negated
        * floats and literals in particular) are not yet folded.

test/files/neg/deprecated-annots.check

@@ -0,0 +1,6 @@
+deprecated-annots.scala:9: warning: @scala.annotation.elidable is ignored in Scala 3
+  @annotation.elidable(42)
+   ^
+error: No warnings can be incurred under -Werror.
+1 warning
+1 error

test/files/neg/deprecated-annots.scala

@@ -0,0 +1,11 @@
+
+// scalac: -Werror -Xlint -Xsource:3
+
+class C[@specialized A]
+
+class D {
+  def f[@specialized A](a: A): A = a
+
+  @annotation.elidable(42)
+  def g() = println("hello, world")
+}