Add capture checking to scala.caps

TODO.md

@@ -49,7 +49,7 @@
 - [ ] library/src/scala/annotation/unchecked/uncheckedCapabilityLeaks.scala
 - [ ] library/src/scala/annotation/unchecked/uncheckedCaptures.scala
 - [ ] library/src/scala/annotation/unroll.scala
-- [ ] library/src/scala/caps/package.scala
+- [x] library/src/scala/caps/package.scala
 - [ ] library/src/scala/compiletime/ops/any.scala
 - [ ] library/src/scala/compiletime/ops/boolean.scala
 - [ ] library/src/scala/compiletime/ops/double.scala

compiler/src/dotty/tools/dotc/cc/Synthetics.scala

@@ -168,4 +168,4 @@ object Synthetics:
         transformCompareCaptures)
   end transform
 
-end Synthetics
+end Synthetics

library/src/scala/caps/package.scala

@@ -1,6 +1,8 @@
 package scala
 package caps
 
+import language.experimental.captureChecking
+
 import annotation.{experimental, compileTimeOnly, retainsCap}
 
 /**

library/src/scala/compiletime/testing/Error.scala

@@ -1,5 +1,7 @@
 package scala.compiletime.testing
 
+import language.experimental.captureChecking
+
 /** Represents a compile-time error.
  *
  *  @see scala.compiletime.testing.typeCheckErrors

library/src/scala/compiletime/testing/ErrorKind.scala

@@ -1,5 +1,7 @@
 package scala.compiletime.testing
 
+import language.experimental.captureChecking
+
 /** An error can be either a parse-time or a typecheck-time */
 sealed trait ErrorKind // This should be an enum but currently, Dotty lib fails to
                        // compile with an obscure error.

library/src/scala/compiletime/testing/package.scala

@@ -1,6 +1,8 @@
 package scala.compiletime
 package testing
 
+import language.experimental.captureChecking
+
 /** Whether the code type checks in the current context?
  *
  *  An inline definition with a call to `typeChecks` should be transparent.