Split research plugin from experimental compiler version (scala#19841)

Author: nicolasstucki

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

@@ -162,7 +162,7 @@ object Feature:
     do checkExperimentalFeature(s"feature $setting", NoSourcePosition)
 
   def isExperimentalEnabled(using Context): Boolean =
-    (Properties.experimental && !ctx.settings.YnoExperimental.value) || ctx.settings.experimental.value
+    (Properties.unstableExperimentalEnabled && !ctx.settings.YnoExperimental.value) || ctx.settings.experimental.value
 
   /** Handle language import `import language.<prefix>.<imported>` if it is one
    *  of the global imports `pureFunctions` or `captureChecking`. In this case

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

@@ -86,11 +86,12 @@ trait PropertiesTrait {
 
   /** Whether the current version of compiler is experimental
    *
-   *  1. Snapshot, nightly releases and non-bootstrapped compiler are experimental.
-   *  2. Features supported by experimental versions of the compiler:
-   *     - research plugins
+   *  Snapshot, nightly releases and non-bootstrapped compiler are experimental.
    */
-  val experimental: Boolean = versionString.contains("SNAPSHOT") || versionString.contains("NIGHTLY") || versionString.contains("nonbootstrapped")
+  val unstableExperimentalEnabled: Boolean = versionString.contains("SNAPSHOT") || versionString.contains("NIGHTLY") || versionString.contains("nonbootstrapped")
+
+  /** Whether the current version of compiler supports research plugins. */
+  val researchPluginEnabled: Boolean = versionString.contains("SNAPSHOT") || versionString.contains("NIGHTLY") || versionString.contains("nonbootstrapped")
 
   val copyrightString: String       = scalaPropOrElse("copyright.string", "(c) 2002-2017 LAMP/EPFL")
 

compiler/src/dotty/tools/dotc/plugins/Plugins.scala

@@ -129,7 +129,7 @@ trait Plugins {
     val updatedPlan = Plugins.schedule(plan, pluginPhases)
 
     // add research plugins
-    if Properties.experimental && !ctx.settings.YnoExperimental.value then
+    if Properties.researchPluginEnabled then
       plugins.collect { case p: ResearchPlugin => p }.foldRight(updatedPlan) {
         (plug, plan) => plug.init(options(plug), plan)
       }