SI-7494 Each plugin must only be instantiated once.

The old behavior was that Plugin.loadAllFrom took a distinct
list of plugin locations.

The broken behavior incorrectly punted to the pruning
algorithm in Plugins.loadPlugins$pick.

The new behavior is to distinctify the list of class names
to load.

This is more robust; under the old scheme, specifying the
continuations.jar under two file names would fail as
described in the ticket.

Pruning a plugin by disabling (-Xplugin-disable) or because
it steps on someone else's phase name suffers the same
defect. There is no way to tell the plugin it has been
benched. And you know that global I gave you?  Can I
have it back?

1 files changed, 4 insertions, 7 deletions

diff --git a/src/compiler/scala/tools/nsc/plugins/Plugin.scala b/src/compiler/scala/tools/nsc/plugins/Plugin.scala
index b0113f7696..a584a4ed5d 100644
--- a/src/compiler/scala/tools/nsc/plugins/Plugin.scala
+++ b/src/compiler/scala/tools/nsc/plugins/Plugin.scala
@@ -93,15 +93,13 @@ object Plugin {
   type AnyClass = Class[_]
 
   /** Use a class loader to load the plugin class.
-   *
-   *  @return `None` on failure
    */
-  def load(pd: PluginDescription, loader: ClassLoader): Try[AnyClass] = {
+  def load(classname: String, loader: ClassLoader): Try[AnyClass] = {
     Try[AnyClass] {
-      loader loadClass pd.classname
+      loader loadClass classname
     } recoverWith {
       case _: Exception =>
-        Failure(new RuntimeException(s"Warning: class not found: ${pd.classname}"))
+        Failure(new RuntimeException(s"Warning: class not found: ${classname}"))
     }
   }
 
@@ -137,9 +135,8 @@ object Plugin {
       case _                   => false
     }
     val (locs, pds) = ((explicit ::: exploded ::: included) filterNot ignored).unzip
-
     val loader = loaderFor(locs.distinct)
-    pds filter (_.isSuccess) map (_.get) map (Plugin load (_, loader))
+    (pds filter (_.isSuccess) map (_.get.classname)).distinct map (Plugin load (_, loader))
   }
 
   /** Instantiate a plugin class, given the class and