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: Changes index resolution so that `FROM empty*` resolves to empty set of indices (opposed to error today)
+    and becomes consistent with `GET /empty*/_search`.
+  impact: Makes a valid query check a bit more permissive in case when pattern is resolved to empty set of indices.
+  notable: false

x-pack/plugin/esql/qa/server/src/main/java/org/elasticsearch/xpack/esql/qa/rest/RequestIndexFilteringTestCase.java

@@ -206,11 +206,6 @@ public void testIndicesDontExist() throws IOException {
         assertThat(e.getMessage(), containsString("verification_exception"));
         assertThat(e.getMessage(), anyOf(containsString("Unknown index [foo]"), containsString("Unknown index [remote_cluster:foo]")));
 
-        e = expectThrows(ResponseException.class, () -> runEsql(timestampFilter("gte", "2020-01-01").query(from("foo*"))));
-        assertEquals(400, e.getResponse().getStatusLine().getStatusCode());
-        assertThat(e.getMessage(), containsString("verification_exception"));
-        assertThat(e.getMessage(), anyOf(containsString("Unknown index [foo*]"), containsString("Unknown index [remote_cluster:foo*]")));
-
         e = expectThrows(ResponseException.class, () -> runEsql(timestampFilter("gte", "2020-01-01").query("FROM foo, test1")));
         assertEquals(404, e.getResponse().getStatusLine().getStatusCode());
         assertThat(e.getMessage(), containsString("index_not_found_exception"));

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

@@ -112,23 +112,20 @@ public void testResolvesExclusionPattern() {
             assertOk(response);
             assertResultConcreteIndices(response, "index-1");// excludes pattern from pattern
         }
-        expectThrows(
-            VerificationException.class,
-            containsString("Unknown index [index-*,-*]"),
-            () -> run(syncEsqlQueryRequest().query("FROM index-*,-* METADATA _index")) // exclude all resolves to empty
-        );
+        try (var response = run(syncEsqlQueryRequest().query("FROM index-*,-* METADATA _index"))) {
+            assertOk(response);
+            assertResultConcreteIndices(response);// exclude all resolves to empty
+        }
     }
 
-    public void testDoesNotResolveEmptyPattern() {
+    public void testResolveEmptyPattern() {
         assertAcked(client().admin().indices().prepareCreate("data"));
         indexRandom(true, "data", 1);
 
-        expectThrows(
-            VerificationException.class,
-            containsString("Unknown index [index-*]"),
-            () -> run(syncEsqlQueryRequest().query("FROM index-* METADATA _index"))
-        );
-
+        try (var response = run(syncEsqlQueryRequest().query("FROM index-* METADATA _index"))) {
+            assertOk(response);
+            assertResultConcreteIndices(response);
+        }
         try (var response = run(syncEsqlQueryRequest().query("FROM data,index-* METADATA _index"))) {
             assertOk(response);
             assertResultConcreteIndices(response, "data");

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

@@ -41,6 +41,10 @@ public static IndexResolution invalid(String invalid) {
         return new IndexResolution(null, invalid, Set.of(), Map.of());
     }
 
+    public static IndexResolution empty(String indexPattern) {
+        return IndexResolution.valid(new EsIndex(indexPattern, Map.of(), Map.of()));
+    }
+
     public static IndexResolution notFound(String name) {
         Objects.requireNonNull(name, "name must not be null");
         return invalid("Unknown index [" + name + "]");

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

@@ -531,6 +531,10 @@ private PreAnalysisResult receiveLookupIndexResolution(
             // If the index resolution is invalid, don't bother with the rest of the analysis
             return result.addLookupIndexResolution(index, lookupIndexResolution);
         }
+        if (lookupIndexResolution.get().concreteIndices().isEmpty()) {
+            // require non empty lookup index
+            return result.addLookupIndexResolution(index, IndexResolution.notFound(lookupIndexResolution.get().name()));
+        }
         if (executionInfo.getClusters().isEmpty() || executionInfo.isCrossClusterSearch() == false) {
             // Local only case, still do some checks, since we moved analysis checks here
             if (lookupIndexResolution.get().indexNameWithModes().isEmpty()) {
@@ -696,9 +700,7 @@ 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