SI-7974 Fix over-eager optimization of Symbol literals

A classic mistake of discarding a non-trivial qualifier.

We actually should have fixed this before merging #3149, as it
was raised in review, but I suppose we got too caught up in the
difficulty of resolving the right overload of `Symbol_apply` that we
forgot.

src/compiler/scala/tools/nsc/transform/CleanUp.scala

@@ -520,7 +520,9 @@ abstract class CleanUp extends Statics with Transform with ast.TreeDSL {
       * And, finally, be advised - Scala's Symbol literal (scala.Symbol) and the Symbol class of the compiler
       * have little in common.
       */
-      case Apply(fn, (arg @ Literal(Constant(symname: String))) :: Nil) if fn.symbol == Symbol_apply && !currentClass.isTrait =>
+      case Apply(fn @ Select(qual, _), (arg @ Literal(Constant(symname: String))) :: Nil)
+        if treeInfo.isQualifierSafeToElide(qual) && fn.symbol == Symbol_apply && !currentClass.isTrait =>
+
         def transformApply = {
           // add the symbol name to a map if it's not there already
           val rhs = gen.mkMethodCall(Symbol_apply, arg :: Nil)

test/files/run/t8933c.scala

@@ -0,0 +1,14 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    try {    
+      {throw T; Symbol}.apply("a")
+      assert(false, "exception not thrown")
+    } catch {
+      case T => // ok
+      case t: Throwable =>
+        assert(false, "wrong not thrown: " + t)
+    }
+  }
+}
+
+object T extends Throwable