Merge pull request scala#8345 from retronym/topic/plugin-classloader-tweak

Use the first scalac-plugin.xml from the plugin classpath

Author: retronym

src/compiler/scala/tools/nsc/plugins/Plugin.scala

@@ -152,9 +152,9 @@ object Plugin {
 
     val fromLoaders = paths.map {path =>
       val loader = findPluginClassloader(path)
-      loader.getResources(PluginXML).asScala.toList.lastOption match {
-        case None => Failure(new MissingPluginException(path))
-        case Some(url) =>
+      loader.getResource(PluginXML) match {
+        case null => Failure(new MissingPluginException(path))
+        case url =>
           val inputStream = url.openStream
           try {
             Try((PluginDescription.fromXML(inputStream), loader))

src/compiler/scala/tools/nsc/plugins/Plugins.scala

@@ -62,7 +62,8 @@ trait Plugins { global: Global =>
   /**
     * Locate or create the classloader to load a compiler plugin with `classpath`.
     *
-    * Subclasses may override to customise the behaviour.
+    * Subclasses may override to customise the behaviour. The returned classloader must return the first
+    * from plugin descriptor from `classpath` when `getResource("scalac-plugin.xml")` is called.
     *
     * @param classpath
     * @return