Mark classes compiled under -Ycc with a CaptureChecked annotation

Author: odersky

Diff for: compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -972,6 +972,7 @@ class Definitions {
   @tu lazy val BooleanBeanPropertyAnnot: ClassSymbol = requiredClass("scala.beans.BooleanBeanProperty")
   @tu lazy val BodyAnnot: ClassSymbol = requiredClass("scala.annotation.internal.Body")
   @tu lazy val CapabilityAnnot: ClassSymbol = requiredClass("scala.annotation.capability")
+  @tu lazy val CaptureCheckedAnnot: ClassSymbol = requiredClass("scala.annotation.internal.CaptureChecked")
   @tu lazy val ChildAnnot: ClassSymbol = requiredClass("scala.annotation.internal.Child")
   @tu lazy val ContextResultCountAnnot: ClassSymbol = requiredClass("scala.annotation.internal.ContextResultCount")
   @tu lazy val ProvisionalSuperClassAnnot: ClassSymbol = requiredClass("scala.annotation.internal.ProvisionalSuperClass")

Diff for: compiler/src/dotty/tools/dotc/transform/PostTyper.scala

@@ -388,13 +388,13 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
                 for parent <- impl.parents do
                   Checking.checkTraitInheritance(parent.tpe.classSymbol, sym.asClass, parent.srcPos)
             // Add SourceFile annotation to top-level classes
-            if sym.owner.is(Package)
-               && ctx.compilationUnit.source.exists
-               && sym != defn.SourceFileAnnot
-            then
-              val reference = ctx.settings.sourceroot.value
-              val relativePath = util.SourceFile.relativePath(ctx.compilationUnit.source, reference)
-              sym.addAnnotation(Annotation.makeSourceFile(relativePath))
+            if sym.owner.is(Package) then
+              if ctx.compilationUnit.source.exists && sym != defn.SourceFileAnnot then
+                val reference = ctx.settings.sourceroot.value
+                val relativePath = util.SourceFile.relativePath(ctx.compilationUnit.source, reference)
+                sym.addAnnotation(Annotation.makeSourceFile(relativePath))
+              if ctx.settings.Ycc.value && sym != defn.CaptureCheckedAnnot then
+                sym.addAnnotation(Annotation(defn.CaptureCheckedAnnot))
           else (tree.rhs, sym.info) match
             case (rhs: LambdaTypeTree, bounds: TypeBounds) =>
               VarianceChecker.checkLambda(rhs, bounds)

Diff for: library/src/scala/annotation/internal/CaptureChecked.scala

@@ -0,0 +1,8 @@
+package scala.annotation
+package internal
+
+/** A marker annotation on a toplevel class that indicates
+ *  that the class was checked under -Ycc
+ */
+class CaptureChecked extends StaticAnnotation
+