refactor out fresh name prefix extraction logic

1. refactor out FreshNameExtractor out of Quasiquotes cake into
   SymbolTable (can’t put it outside due to the fact that names are
   path-dependent)

2. add optional parameter to the fresh name creator to cover additional
   qq$ prefix needed for quasiquotes

3. add unit tests

2 files changed, 53 insertions, 7 deletions

diff --git a/test/files/scalacheck/quasiquotes/QuasiquoteProperties.scala b/test/files/scalacheck/quasiquotes/QuasiquoteProperties.scala
index b2bce124ee..d398c254fb 100644
--- a/test/files/scalacheck/quasiquotes/QuasiquoteProperties.scala
+++ b/test/files/scalacheck/quasiquotes/QuasiquoteProperties.scala
@@ -18,13 +18,12 @@ trait Helpers {
 
   object simplify extends Transformer {
     object SimplifiedName {
-      def unapply[T <: Name](name: T): Option[T] =
-        name.toString.split("\\$").toSeq match {
-          case first :+ last if scala.util.Try(last.toInt).isSuccess && first.nonEmpty =>
-            val value = first.mkString("", "$", "$")
-            Some((if (name.isTermName) TermName(value) else TypeName(value)).asInstanceOf[T])
-          case _ => None
-        }
+      val st = scala.reflect.runtime.universe.asInstanceOf[scala.reflect.internal.SymbolTable]
+      val FreshName = new st.FreshNameExtractor
+      def unapply[T <: Name](name: T): Option[T] = name.asInstanceOf[st.Name] match {
+        case FreshName(prefix) =>
+          Some((if (name.isTermName) TermName(prefix) else TypeName(prefix)).asInstanceOf[T])
+      }
     }
 
     override def transform(tree: Tree): Tree = tree match {
diff --git a/test/junit/scala/tools/nsc/symtab/FreshNameExtractorTest.scala b/test/junit/scala/tools/nsc/symtab/FreshNameExtractorTest.scala
new file mode 100644
index 0000000000..cf09abdfff
--- /dev/null
+++ b/test/junit/scala/tools/nsc/symtab/FreshNameExtractorTest.scala
@@ -0,0 +1,47 @@
+package scala.tools.nsc
+package symtab
+
+import org.junit.Assert._
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+
+import scala.tools.testing.AssertUtil.assertThrows
+import scala.reflect.internal.util.FreshNameCreator
+
+@RunWith(classOf[JUnit4])
+class FreshNameExtractorTest {
+  object symbolTable extends SymbolTableForUnitTesting
+  import symbolTable._
+
+  val prefixes = List("foo$", "x$", "bar", "bippy$baz$")
+
+  @Test
+  def extractionPreservesPrefix =
+    ("" :: prefixes).foreach { creatorPrefix =>
+      prefixes.foreach { newPrefix =>
+        val Creator = new FreshNameCreator(creatorPrefix)
+        val Extractor = new FreshNameExtractor(creatorPrefix)
+        val Extractor(extractedPrefix) = TermName(Creator.newName(newPrefix))
+        assertEquals(newPrefix, extractedPrefix)
+      }
+    }
+
+  @Test
+  def extractionFailsOnCreatorPrefixMismatch = {
+    val Creator = new FreshNameCreator(prefixes.head)
+    val Extractor = new FreshNameExtractor(prefixes.tail.head)
+    assertThrows[MatchError] {
+      val Extractor(_) = TermName(Creator.newName("foo"))
+    }
+  }
+
+  @Test
+  def extractionsFailsIfNameDoesntEndWithNumber = {
+    val Creator = new FreshNameCreator(prefixes.head)
+    val Extractor = new FreshNameExtractor(prefixes.head)
+    assertThrows[MatchError] {
+      val Extractor(_) = TermName(Creator.newName("foo") + "bar")
+    }
+  }
+}
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