ES|QL Empty index resolution

docs/changelog/135601.yaml

@@ -0,0 +1,12 @@
+pr: 135601
+summary: ES|QL Empty index resolution
+area: ES|QL
+type: breaking
+issues: []
+breaking:
+  title: ES|QL Empty index resolution
+  area: ES|QL
+  details: Please describe the details of this change for the release notes. You can
+    use asciidoc.
+  impact: Please describe the impact of this change to users
+  notable: false

x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/plugin/IndexResolutionIT.java

@@ -104,12 +104,18 @@ public void testDoesNotResolveMissingIndex() {
         );
     }
 
-    public void testDoesNotResolveEmptyPattern() {
-        expectThrows(
-            VerificationException.class,
-            containsString("Unknown index [index-*]"),
-            () -> run(syncEsqlQueryRequest().query("FROM index-*"))
-        );
+    public void testResolveEmptyPattern() {
+        assertAcked(client().admin().indices().prepareCreate("data"));
+        indexRandom(true, "data", 1);
+
+        try (var response = run(syncEsqlQueryRequest().query("FROM data,index-* METADATA _index"))) {
+            assertOk(response);
+            assertResultConcreteIndices(response, "data");
+        }
+        try (var response = run(syncEsqlQueryRequest().query("FROM index-* METADATA _index"))) {
+            assertOk(response);
+            assertResultConcreteIndices(response);
+        }
     }
 
     public void testDoesNotResolveClosedIndex() {

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/index/IndexResolution.java

@@ -41,9 +41,8 @@ public static IndexResolution invalid(String invalid) {
         return new IndexResolution(null, invalid, Set.of(), Map.of());
     }
 
-    public static IndexResolution notFound(String name) {
-        Objects.requireNonNull(name, "name must not be null");
-        return invalid("Unknown index [" + name + "]");
+    public static IndexResolution empty(String indexPattern) {
+        return IndexResolution.valid(new EsIndex(indexPattern, Map.of(), Map.of()));
     }
 
     private final EsIndex index;

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/session/EsqlSession.java

@@ -696,9 +696,7 @@ private void preAnalyzeMainIndices(
             String indexExpressionToResolve = EsqlCCSUtils.createIndexExpressionFromAvailableClusters(executionInfo);
             if (indexExpressionToResolve.isEmpty()) {
                 // if this was a pure remote CCS request (no local indices) and all remotes are offline, return an empty IndexResolution
-                listener.onResponse(
-                    result.withIndices(IndexResolution.valid(new EsIndex(preAnalysis.indexPattern().indexPattern(), Map.of(), Map.of())))
-                );
+                listener.onResponse(result.withIndices(IndexResolution.empty(preAnalysis.indexPattern().indexPattern())));
             } else {
                 indexResolver.resolveAsMergedMapping(
                     indexExpressionToResolve,

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/session/IndexResolver.java

@@ -106,7 +106,7 @@ public static IndexResolution mergedMappings(String indexPattern, FieldsInfo fie
         assert ThreadPool.assertCurrentThreadPool(ThreadPool.Names.SEARCH_COORDINATION); // too expensive to run this on a transport worker
         int numberOfIndices = fieldsInfo.caps.getIndexResponses().size();
         if (numberOfIndices == 0) {
-            return IndexResolution.notFound(indexPattern);
+            return IndexResolution.empty(indexPattern);
         }
 
         // For each field name, store a list of the field caps responses from each index