1 files changed, 19 insertions, 7 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Environment.java b/src/main/java/com/google/devtools/build/lib/syntax/Environment.java
index 9b17cead89..38cbb7c35f 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Environment.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Environment.java
@@ -940,16 +940,28 @@ public final class Environment implements Freezable {
     }
   }
 
+  /** An exception thrown by {@link #FAIL_FAST_HANDLER}. */
+  // TODO(bazel-team): Possibly extend RuntimeException instead of IllegalArgumentException.
+  public static class FailFastException extends IllegalArgumentException {
+    public FailFastException(String s) {
+      super(s);
+    }
+  }
 
   /**
-   * The fail fast handler, which throws an {@link IllegalArgumentException} whenever an error or
-   * warning occurs.
+   * A handler that immediately throws {@link FailFastException} whenever an error or warning
+   * occurs.
+   *
+   * We do not reuse an existing unchecked exception type, because callers (e.g., test assertions)
+   * need to be able to distinguish between organically occurring exceptions and exceptions thrown
+   * by this handler.
    */
   public static final EventHandler FAIL_FAST_HANDLER = new EventHandler() {
-      @Override
-      public void handle(Event event) {
-        Preconditions.checkArgument(
-            !EventKind.ERRORS_AND_WARNINGS.contains(event.getKind()), event);
+    @Override
+    public void handle(Event event) {
+      if (EventKind.ERRORS_AND_WARNINGS.contains(event.getKind())) {
+        throw new FailFastException(event.toString());
       }
-    };
+    }
+  };
 }