Add scala.language.experimental.mode

Author: nicolasstucki

compiler/src/dotty/tools/dotc/config/Feature.scala

@@ -23,6 +23,7 @@ object Feature:
   private val genericNumberLiterals = experimental("genericNumberLiterals")
   val scala2macros = experimental("macros")
 
+  val mode = experimental("mode")
   val dependent = experimental("dependent")
   val erasedDefinitions = experimental("erasedDefinitions")
   val symbolLiterals = deprecated("symbolLiterals")
@@ -37,6 +38,7 @@ object Feature:
   // TODO compute this list
   // TODO remove features that do not enable experimental mode
   val experimentalAutoEnableFeatures: List[TermName] = List(
+    mode,
     namedTypeArguments,
     genericNumberLiterals,
     erasedDefinitions,

library/src/scala/runtime/stdLibPatches/language.scala

@@ -20,6 +20,14 @@ object language:
    */
   object experimental:
 
+    /** Enable use of experimental APIs by making the current scope an experimental one.
+     *
+     * @see [[https://dotty.epfl.ch/docs/reference/other-new-features/experimental-defs]]
+     */
+    @compileTimeOnly("`mode` can only be used at compile time in import statements")
+    object mode
+
+
     /* Experimental support for richer dependent types (disabled for now)
      * One can still run the compiler with support for parsing singleton applications
      * using command line option `-language:experimental.dependent`.

project/MiMaFilters.scala

@@ -8,6 +8,8 @@ object MiMaFilters {
     val ForwardsBreakingChanges: Map[String, Seq[ProblemFilter]] = Map(
       // Additions that require a new minor version of the library
       Build.previousDottyVersion -> Seq(
+        ProblemFilters.exclude[MissingFieldProblem]("scala.runtime.stdLibPatches.language#experimental.mode"),
+        ProblemFilters.exclude[MissingClassProblem]("scala.runtime.stdLibPatches.language$experimental$mode$"),
       ),
 
       // Additions since last LTS

tests/pos/experimental-mode.scala

@@ -0,0 +1,9 @@
+//> using option -Yno-experimental
+
+import scala.language.experimental.mode
+import scala.annotation.experimental
+
+@experimental
+def foo = 1
+
+def bar = foo // made `@experimental` by `scala.language.experimental.mode`