[ML] Data frame analytics _explain API should not fail when none field is included

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportExplainDataFrameAnalyticsAction.java

@@ -17,6 +17,7 @@
 import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.license.LicenseUtils;
 import org.elasticsearch.license.XPackLicenseState;
 import org.elasticsearch.tasks.Task;
@@ -106,7 +107,7 @@ private void explain(Task task, PutDataFrameAnalyticsAction.Request request,
         );
         if (licenseState.isSecurityEnabled()) {
             useSecondaryAuthIfAvailable(this.securityContext, () -> {
-                // Set the auth headers (preferring the secondary headers) to the caller's. 
+                // Set the auth headers (preferring the secondary headers) to the caller's.
                 // Regardless if the config was previously stored or not.
                 DataFrameAnalyticsConfig config = new DataFrameAnalyticsConfig.Builder(request.getConfig())
                     .setHeaders(filterSecurityHeaders(threadPool.getThreadContext().getHeaders()))
@@ -152,6 +153,11 @@ private void estimateMemoryUsage(Task task,
                                      DataFrameAnalyticsConfig config,
                                      ExtractedFields extractedFields,
                                      ActionListener<MemoryEstimation> listener) {
+        if (extractedFields.getAllFields().isEmpty()) {
+            listener.onResponse(new MemoryEstimation(ByteSizeValue.ZERO, ByteSizeValue.ZERO));
+            return;
+        }
+
         final String estimateMemoryTaskId = "memory_usage_estimation_" + task.getId();
         DataFrameDataExtractorFactory extractorFactory = DataFrameDataExtractorFactory.createForSourceIndices(
             new ParentTaskAssigningClient(client, task.getParentTaskId()), estimateMemoryTaskId, config, extractedFields);

x-pack/plugin/src/test/resources/rest-api-spec/test/ml/explain_data_frame_analytics.yml

@@ -312,3 +312,35 @@
   - match: { field_selection.4.is_required: false }
   - match: { field_selection.4.feature_type: "categorical" }
   - is_false: field_selection.4.reason
+
+---
+"Test given no included field":
+
+  - do:
+      indices.create:
+        index: index-source
+        body:
+          mappings:
+            properties:
+              x:
+                type: keyword
+
+  - do:
+      index:
+        index: index-source
+        refresh: true
+        body: { x: "hello!" }
+  - match: { result: "created" }
+
+  - do:
+      ml.explain_data_frame_analytics:
+        body:
+          source: { index: "index-source" }
+          analysis: { outlier_detection: {} }
+  - match:
+      memory_estimation.expected_memory_without_disk: "0"
+  - match:
+      memory_estimation.expected_memory_with_disk: "0"
+  - length: { field_selection: 1 }
+  - match: { field_selection.0.name: "x" }
+  - match: { field_selection.0.is_included: false }