More info about exceptions without messages (#48) (#49)

plugin/src/main/scala/org/scalafmt/sbt/ScalafmtSbtReporter.scala

@@ -7,14 +7,21 @@ import org.scalafmt.interfaces.ScalafmtReporter
 import sbt.internal.util.MessageOnlyException
 import sbt.util.Logger
 
+import scala.util.control.NoStackTrace
+
 class ScalafmtSbtReporter(log: Logger, writer: PrintWriter)
     extends ScalafmtReporter {
   override def error(file: Path, message: String): Unit = {
     throw new MessageOnlyException(s"$message: $file")
   }
 
-  override def error(file: Path, e: Throwable): Unit =
-    error(file, e.getMessage)
+  override def error(file: Path, e: Throwable): Unit = {
+    if (e.getMessage != null) {
+      error(file, e.getMessage)
+    } else {
+      throw new FailedToFormat(file.toString, e)
+    }
+  }
 
   override def excluded(file: Path): Unit =
     log.debug(s"file excluded: $file")
@@ -23,4 +30,8 @@ class ScalafmtSbtReporter(log: Logger, writer: PrintWriter)
     log.debug(s"parsed config (v$scalafmtVersion): $config")
 
   override def downloadWriter(): PrintWriter = writer
+
+  private class FailedToFormat(filename: String, cause: Throwable)
+      extends Exception(filename, cause)
+      with NoStackTrace
 }