Updated additional contract validation error to include ref

src/main/java/io/vertx/openapi/contract/OpenAPIContract.java

@@ -116,7 +116,16 @@ static Future<OpenAPIContract> from(Vertx vertx, JsonObject unresolvedContract,
         //  method and reused below.
         JsonObject file = additionalContractFiles.get(ref);
         Future<?> validationFuture = version.validateAdditionalContractFile(vertx, repository, file)
-          .compose(v -> vertx.executeBlocking(() -> repository.dereference(ref, JsonSchema.of(ref, file))));
+          .compose(v -> vertx.executeBlocking(() -> repository.dereference(ref, JsonSchema.of(ref, file))))
+          .transform(ar -> {
+            if (ar.failed()) {
+              return Future.failedFuture(
+                createInvalidContract("Failed to validate additional contract file: " + ref, ar.cause())
+              );
+            } else {
+              return (Future<?>) ar;
+            }
+          });
 
         validationFutures.add(validationFuture);
       }

src/test/java/io/vertx/tests/contract/OpenAPIContractTest.java

@@ -194,8 +194,10 @@ void testMalformedJsonSchemaProvidedAsAdditionalSpecFiles(Vertx vertx, VertxTest
         assertTrue(handler.failed());
         assertThat(handler.cause()).isInstanceOf(OpenAPIContractException.class);
         assertThat(handler.cause()).hasMessageThat()
-          .isEqualTo("The passed OpenAPI contract is invalid: Found issue in specification for reference:" +
-            " -1 is less than 0");
+          .isEqualTo("The passed OpenAPI contract is invalid: Failed to validate additional contract file: " +
+            "https://example.com/petstore");
+        assertThat(handler.cause().getCause()).hasMessageThat()
+          .isEqualTo("-1 is less than 0");
         testContext.completeNow();
       }));
   }