Avoid compilerSupportsExperimental variable in Config

Instead, use a special exclude if vulpix.ParallelTesting is in the stack trace.

Author: odersky

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

@@ -215,16 +215,4 @@ object Config {
    *  reduces the number of allocated denotations by ~50%.
    */
   inline val reuseSymDenotations = true
-
-  /** Turn on in order to test the CI assuming we have a stable release compiler
-   *  instead of a nightly or snapshot.
-   */
-  private val assumeNonExperimentalCompiler = false
-
-  /** Are experimental features are allowed? By default same as
-   *  `Properties.experimental`. Can be re-assigned, e.g. to allow tests
-   *  of experimental features.
-   */
-  @sharable private[dotty] var compilerSupportsExperimental =
-    Properties.experimental && !assumeNonExperimentalCompiler
 }

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

@@ -97,11 +97,16 @@ object Feature:
     else
       false
 
-  def compilerSupportsExperimental(using Context) =
-    Config.compilerSupportsExperimental && !ctx.settings.YnoExperimental.value
+  private val assumeExperimentalIn = Set("dotty.tools.vulpix.ParallelTesting")
 
   def checkExperimentalFeature(which: String, srcPos: SrcPos = NoSourcePosition)(using Context) =
-    if !compilerSupportsExperimental then
+    def hasSpecialPermission =
+      new Exception().getStackTrace.exists(elem =>
+        assumeExperimentalIn.exists(elem.getClassName().startsWith(_)))
+    if !(Properties.experimental || hasSpecialPermission)
+       || ctx.settings.YnoExperimental.value
+    then
+      //println(i"${new Exception().getStackTrace.map(_.getClassName).toList}%\n%")
       report.error(i"Experimental feature$which may only be used with nightly or snapshot version of compiler", srcPos)
 
   /** Check that experimental compiler options are only set for snapshot or nightly compiler versions. */

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -39,8 +39,6 @@ import dotty.tools.vulpix.TestConfiguration.defaultOptions
 trait ParallelTesting extends RunnerOrchestration { self =>
   import ParallelTesting._
 
-  Config.compilerSupportsExperimental = true
-
   /** If the running environment supports an interactive terminal, each `Test`
    *  will be run with a progress bar and real time feedback
    */