Handle cases for when a swoval PathWatchers.Event's RelPath has no last segment available

Author: Gedochao

modules/build/src/main/scala/scala/build/Build.scala

@@ -702,11 +702,17 @@ object Build {
           case d: Directory =>
             // Filtering event for directories, to ignore those related to the .bloop directory in particular
             event =>
-              val p           = os.Path(event.getTypedPath.getPath.toAbsolutePath)
-              val relPath     = p.relativeTo(d.path)
-              val isHidden    = relPath.segments.exists(_.startsWith("."))
-              def isScalaFile = relPath.last.endsWith(".sc") || relPath.last.endsWith(".scala")
-              def isJavaFile  = relPath.last.endsWith(".java")
+              val p        = os.Path(event.getTypedPath.getPath.toAbsolutePath)
+              val relPath  = p.relativeTo(d.path)
+              val isHidden = relPath.segments.exists(_.startsWith("."))
+              val pathLast = Try(relPath.last).toEither.orElse(Try(p.last).toEither) match {
+                case Right(last) => last
+                case Left(e) =>
+                  logger.log(WatchError(event, e))
+                  ""
+              }
+              def isScalaFile = pathLast.endsWith(".sc") || pathLast.endsWith(".scala")
+              def isJavaFile  = pathLast.endsWith(".java")
               !isHidden && (isScalaFile || isJavaFile)
           case _ => _ => true
         }

modules/core/src/main/scala/scala/build/errors/WatchError.scala

@@ -0,0 +1,10 @@
+package scala.build.errors
+
+import com.swoval.files.PathWatchers
+
+class WatchError(event: PathWatchers.Event, cause: Throwable = null)
+    extends BuildException(
+      message = s"Error watching paths with the PathWatchers.Event: $event",
+      positions = Nil,
+      cause = cause
+    )