Prevent printing stack trace of ScalacInvoker on known compilation er…

…rors

src/java/io/bazel/rulesscala/scalac/ScalacInvoker.java

@@ -24,11 +24,11 @@ public static ScalacInvokerResults invokeCompiler(CompileOptions ops, String[] c
       comp.process(compilerArgs);
     } catch (Throwable ex) {
       if (ex.toString().contains("scala.reflect.internal.Types$TypeError")) {
-        throw new RuntimeException("Build failure with type error", ex);
+        throw new ScalacWorker.CompilationFailed("with type error", ex);
       } else if (ex.toString().contains("java.lang.StackOverflowError")) {
-        throw new RuntimeException("Build failure with StackOverflowError", ex);
+        throw new ScalacWorker.CompilationFailed("with StackOverflowError", ex);
       } else if (isMacroException(ex)) {
-        throw new RuntimeException("Build failure during macro expansion", ex);
+        throw new ScalacWorker.CompilationFailed("during macro expansion", ex);
       } else {
         throw ex;
       }
@@ -58,7 +58,7 @@ public static ScalacInvokerResults invokeCompiler(CompileOptions ops, String[] c
 
     if (reporter.hasErrors()) {
       reporter.flush();
-      throw new RuntimeException("Build failed");
+      throw new ScalacWorker.CompilationFailed("with errors.");
     }
 
     return results;

src/java/io/bazel/rulesscala/scalac/ScalacInvoker3.java

@@ -44,7 +44,7 @@ public static ScalacInvokerResults invokeCompiler(CompileOptions ops, String[] c
 
     if (reporter.hasErrors()) {
 //      reporter.flush();
-      throw new RuntimeException("Build failed");
+      throw new ScalacWorker.CompilationFailed("with errors.");
     }
 
     return results;

src/java/io/bazel/rulesscala/scalac/ScalacWorker.java

@@ -32,6 +32,15 @@ public InvalidSettings() {
     }
   }
 
+  public static class CompilationFailed extends WorkerException {
+    public CompilationFailed(String reason, Throwable cause) {
+      super("Compilation failed " + reason, cause);
+    }
+    public CompilationFailed(String reason) {
+      this(reason, null);
+    }
+  }
+
   private static final boolean isWindows =
       System.getProperty("os.name").toLowerCase().contains("windows");
 

src/java/io/bazel/rulesscala/worker/Worker.java

@@ -33,6 +33,9 @@ public abstract class WorkerException extends RuntimeException {
 			public WorkerException(String message) {
 				super(message);
 			}
+      public WorkerException(String message, Throwable cause) {
+				super(message, cause);
+			}
 		}
   }