[ML] Disable CrossProject for Datafeeds

Initially, Datafeeds will not support cross-project source indices. We
will verify that the IndicesOptions is not trying to resolve a
cross-project index expression and throw a cross-project specific error
message.

Author: prwhelan

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedConfig.java

@@ -1050,6 +1050,10 @@ public DatafeedConfig build() {
             if (indicesOptions == null) {
                 indicesOptions = IndicesOptions.STRICT_EXPAND_OPEN_HIDDEN_FORBID_CLOSED;
             }
+            if (indicesOptions.resolveCrossProjectIndexExpression()) {
+                throw ExceptionsHelper.crossProjectSearchIsDisabled();
+            }
+
             return new DatafeedConfig(
                 id,
                 jobId,

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/utils/ExceptionsHelper.java

@@ -101,6 +101,10 @@ public static ElasticsearchStatusException taskOperationFailureToStatusException
         return new ElasticsearchStatusException(failure.getCause().getMessage(), failure.getStatus(), failure.getCause());
     }
 
+    public static ElasticsearchStatusException crossProjectSearchIsDisabled() {
+        return new ElasticsearchStatusException("Cross-project search is not enabled for any ML feature", RestStatus.FORBIDDEN);
+    }
+
     /**
      * Creates an error message that explains there are shard failures, displays info
      * for the first failure (shard/reason) and kindly asks to see more info in the logs

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedConfigBuilderTests.java

@@ -6,12 +6,14 @@
  */
 package org.elasticsearch.xpack.core.ml.datafeed;
 
+import org.elasticsearch.ElasticsearchStatusException;
 import org.elasticsearch.action.search.SearchRequest;
 import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.core.TimeValue;
+import org.elasticsearch.rest.RestStatus;
 import org.elasticsearch.search.SearchModule;
 import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregationBuilders;
@@ -30,6 +32,7 @@
 
 import static org.elasticsearch.xpack.core.ml.datafeed.DatafeedConfigTests.randomStringList;
 import static org.elasticsearch.xpack.core.ml.utils.QueryProviderTests.createTestQueryProvider;
+import static org.hamcrest.Matchers.equalTo;
 
 public class DatafeedConfigBuilderTests extends AbstractWireSerializingTestCase<DatafeedConfig.Builder> {
 
@@ -147,4 +150,17 @@ protected Writeable.Reader<DatafeedConfig.Builder> instanceReader() {
         return DatafeedConfig.Builder::new;
     }
 
+    public void testResolveCrossProjectIsDisabled() {
+        var datafeedBuilder = createRandomizedDatafeedConfigBuilder("jobId", "datafeed-id", 3600000);
+        datafeedBuilder = datafeedBuilder.setIndicesOptions(
+            IndicesOptions.builder(datafeedBuilder.getIndicesOptions())
+                .crossProjectModeOptions(new IndicesOptions.CrossProjectModeOptions(true))
+                .build()
+        );
+
+        var actualException = assertThrows(ElasticsearchStatusException.class, datafeedBuilder::build);
+        assertThat(actualException.getMessage(), equalTo("Cross-project search is not enabled for any ML feature"));
+        assertThat(actualException.status(), equalTo(RestStatus.FORBIDDEN));
+    }
+
 }