Allow dual Scala 2/3 in non-experimental scopes

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/PruneErasedDefs.scala

@@ -55,7 +55,8 @@ class PruneErasedDefs extends MiniPhase with SymTransformer { thisTransform =>
     tree
 
   def checkErasedInExperimental(sym: Symbol)(using Context): Unit =
-    if sym.is(Erased) && sym != defn.Compiletime_erasedValue && !sym.isInExperimentalScope then
+    // Make an exception for Scala 2 experimental macros to allow dual Scala 2/3 macros under non experimental mode
+    if sym.is(Erased, butNot = Macro) && sym != defn.Compiletime_erasedValue && !sym.isInExperimentalScope then
       Feature.checkExperimentalFeature("erased", sym.sourcePos)
 }
 

tests/pos-custom-args/no-experimental/i8945.scala

@@ -0,0 +1,27 @@
+// src-2/MacroImpl.scala
+trait Context {
+  object universe {
+    type Literal
+  }
+}
+
+class MacroImpl(val c: Context) {
+  import c.universe.*
+  def mono: Literal = ???
+}
+
+// src-3/Macros.scala
+import scala.language.experimental.macros
+
+object Macros {
+
+  object Bundles {
+    def mono: Unit = macro MacroImpl.mono
+    inline def mono: Unit = ${ Macros3.monoImpl }
+  }
+
+  object Macros3 {
+    def monoImpl(using quoted.Quotes) = '{()}
+  }
+
+}