Avoid memory leak in ham-fisted attempt to use WeakMap as a cache

Author: retronym

src/main/scala/scala/async/internal/AsyncMacro.scala

@@ -1,19 +1,20 @@
 package scala.async.internal
 
-import java.util
-
 object AsyncMacro {
-  private val nameCache = new util.WeakHashMap[Object, AsyncNames[_]]()
   def apply(c0: reflect.macros.Context, base: AsyncBase)(body0: c0.Tree): AsyncMacro { val c: c0.type } = {
     import language.reflectiveCalls
-    val asyncNames0 = nameCache.synchronized[AsyncNames[_]] {
-      nameCache.computeIfAbsent(c0.universe, new java.util.function.Function[Object, AsyncNames[_]] {
-        override def apply(t: Object): AsyncNames[_] = new AsyncNames[c0.universe.type](c0.universe)
-      })
+
+    // Use an attachment on RootClass as a sneaky place for a per-Global cache
+    val att = c0.internal.attachments(c0.universe.rootMirror.RootClass)
+    val names = att.get[AsyncNames[_]].getOrElse {
+      val names = new AsyncNames[c0.universe.type](c0.universe)
+      att.update(names)
+      names
     }
+
     new AsyncMacro { self =>
       val c: c0.type                                             = c0
-      val asyncNames: AsyncNames[c.universe.type]                = asyncNames0.asInstanceOf[AsyncNames[c.universe.type]]
+      val asyncNames: AsyncNames[c.universe.type]                = names.asInstanceOf[AsyncNames[c.universe.type]]
       val body: c.Tree = body0
       // This member is required by `AsyncTransform`:
       val asyncBase: AsyncBase                                   = base