SI-8304 Allow volatile-typed Idents as stable ident patterns

As we did for `Select`-s in SI-6815 / fada1ef6.

2 files changed, 39 insertions, 3 deletions

diff --git a/src/reflect/scala/reflect/internal/TreeInfo.scala b/src/reflect/scala/reflect/internal/TreeInfo.scala
index 02db40f1de..b7df2e82cb 100644
--- a/src/reflect/scala/reflect/internal/TreeInfo.scala
+++ b/src/reflect/scala/reflect/internal/TreeInfo.scala
@@ -98,7 +98,7 @@ abstract class TreeInfo {
    */
   def isStableIdentifier(tree: Tree, allowVolatile: Boolean): Boolean =
     tree match {
-      case i @ Ident(_)    => isStableIdent(i)
+      case i @ Ident(_)    => isStableIdent(i, allowVolatile)
       case Select(qual, _) => isStableMemberOf(tree.symbol, qual, allowVolatile) && isPath(qual, allowVolatile)
       case Apply(Select(free @ Ident(_), nme.apply), _) if free.symbol.name endsWith nme.REIFY_FREE_VALUE_SUFFIX =>
         // see a detailed explanation of this trick in `GenSymbols.reifyFreeTerm`
@@ -119,11 +119,11 @@ abstract class TreeInfo {
     typeOk(tree.tpe) && (allowVolatile || !hasVolatileType(tree)) && !definitions.isByNameParamType(tree.tpe)
   )
 
-  private def isStableIdent(tree: Ident): Boolean = (
+  private def isStableIdent(tree: Ident, allowVolatile: Boolean): Boolean = (
        symOk(tree.symbol)
     && tree.symbol.isStable
     && !definitions.isByNameParamType(tree.tpe)
-    && !tree.symbol.hasVolatileType // TODO SPEC: not required by spec
+    && (allowVolatile || !tree.symbol.hasVolatileType) // TODO SPEC: not required by spec
   )
 
   /** Is `tree`'s type volatile? (Ignored if its symbol has the @uncheckedStable annotation.)
diff --git a/test/files/pos/t8301b.scala b/test/files/pos/t8301b.scala
new file mode 100644
index 0000000000..5641547c18
--- /dev/null
+++ b/test/files/pos/t8301b.scala
@@ -0,0 +1,36 @@
+// cf. pos/t8300-patmat.scala
+trait Universe {
+  type Name >: Null <: AnyRef with NameApi
+  trait NameApi
+ 
+  type TermName >: Null <: TermNameApi with Name
+  trait TermNameApi extends NameApi
+}
+ 
+object Test extends App {
+  val u: Universe = ???
+  import u._
+ 
+  val ScalaName: TermName = ???
+  locally {
+    
+    ??? match {
+      case Test.ScalaName => ???
+    }
+    import Test.ScalaName._
+
+    ??? match {
+      case ScalaName => ???
+    }
+    import ScalaName._
+
+    // both the pattern and import led to
+    // stable identifier required, but SN found. Note that value SN 
+    // is not stable because its type, Test.u.TermName, is volatile.
+    val SN = ScalaName
+    ??? match {
+      case SN => ???
+    }
+    import SN._
+  }
+}