Reimplement fallback to system classloader to maintain the 0.13 semantics

util/io/src/main/scala/sbt/IO.scala

@@ -77,13 +77,22 @@ object IO {
    * If the location cannot be determined or if it is not a file, an error is generated.
    * Note that Java standard library classes typically do not have a location associated with them.
    */
-  def classLocationFile(cl: Class[_]): File = {
-    val classURL =
-      Option(cl.getProtectionDomain.getCodeSource).getOrElse {
-        sys.error("No class location for " + cl)
-      }.getLocation
-    toFile(classURL)
-  }
+  def classLocationFile(cl: Class[_]): File =
+    Option(cl.getProtectionDomain.getCodeSource) match {
+      case Some(codeSource) =>
+        val classURL = codeSource.getLocation
+        toFile(classURL)
+      case None =>
+        // NB: This assumes that classes without code sources are System classes, and thus located in
+        // jars. It assumes that `urlAsFile` will truncate to the containing jar file.
+        val clsfile = s"${cl.getName.replace('.', '/')}.class"
+        Option(ClassLoader.getSystemClassLoader.getResource(clsfile))
+          .flatMap {
+            urlAsFile
+          }.getOrElse {
+            sys.error("No class location for " + cl)
+          }
+    }
 
   /**
    * Returns a URL for the classfile containing the given class file for type `T` (as determined by an implicit Manifest).
@@ -104,7 +113,7 @@ object IO {
         sys.error("No class location for " + cl)
       }
     } catch {
-      case e =>
+      case e: Throwable =>
         e.printStackTrace()
         throw e
     }