Disallow CCS with lookup join

docs/changelog/120277.yaml

@@ -0,0 +1,5 @@
+pr: 120277
+summary: Disallow CCS with lookup join
+area: ES|QL
+type: enhancement
+issues: []

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/analysis/Analyzer.java

@@ -11,7 +11,6 @@
 import org.elasticsearch.compute.data.Block;
 import org.elasticsearch.index.IndexMode;
 import org.elasticsearch.logging.Logger;
-import org.elasticsearch.transport.RemoteClusterAware;
 import org.elasticsearch.xpack.core.enrich.EnrichPolicy;
 import org.elasticsearch.xpack.esql.Column;
 import org.elasticsearch.xpack.esql.EsqlIllegalArgumentException;
@@ -660,28 +659,6 @@ private Join resolveLookupJoin(LookupJoin join) {
                     return join;
                 }
 
-                // joining with remote cluster is not supported yet
-                if (join.left() instanceof EsRelation esr) {
-                    for (var index : esr.index().concreteIndices()) {
-                        if (index.indexOf(RemoteClusterAware.REMOTE_CLUSTER_INDEX_SEPARATOR) != -1) {
-                            return join.withConfig(
-                                new JoinConfig(
-                                    type,
-                                    List.of(
-                                        new UnresolvedAttribute(
-                                            join.source(),
-                                            "unsupported",
-                                            "LOOKUP JOIN does not support joining with remote cluster indices [" + esr.index().name() + "]"
-                                        )
-                                    ),
-                                    List.of(),
-                                    List.of()
-                                )
-                            );
-                        }
-                    }
-                }
-
                 JoinType coreJoin = using.coreJoin();
                 // verify the join type
                 if (coreJoin != JoinTypes.LEFT) {

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/parser/LogicalPlanBuilder.java

@@ -15,6 +15,7 @@
 import org.elasticsearch.dissect.DissectException;
 import org.elasticsearch.dissect.DissectParser;
 import org.elasticsearch.index.IndexMode;
+import org.elasticsearch.transport.RemoteClusterAware;
 import org.elasticsearch.xpack.esql.VerificationException;
 import org.elasticsearch.xpack.esql.common.Failure;
 import org.elasticsearch.xpack.esql.core.expression.Alias;
@@ -523,9 +524,15 @@ public PlanFactory visitJoinCommand(EsqlBaseParser.JoinCommandContext ctx) {
         }
 
         var target = ctx.joinTarget();
+        var rightPattern = visitIdentifier(target.index);
+
+        if (RemoteClusterAware.isRemoteIndexName(rightPattern)) {
+            throw new ParsingException(source(target), "LOOKUP JOIN does not support remote cluster indices [{}]", rightPattern);
+        }
+
         UnresolvedRelation right = new UnresolvedRelation(
             source(target),
-            new TableIdentifier(source(target.index), null, visitIdentifier(target.index)),
+            new TableIdentifier(source(target.index), null, rightPattern),
             false,
             emptyList(),
             IndexMode.LOOKUP,
@@ -552,6 +559,18 @@ public PlanFactory visitJoinCommand(EsqlBaseParser.JoinCommandContext ctx) {
             throw new ParsingException(source, "JOIN ON clause only supports one field at the moment, found [{}]", matchFieldsCount);
         }
 
-        return p -> new LookupJoin(source, p, right, joinFields);
+        return p -> {
+            p.forEachUp(UnresolvedRelation.class, r -> {
+                if (RemoteClusterAware.isRemoteIndexName(r.table().index())) {
+                    throw new ParsingException(
+                        source(target),
+                        "LOOKUP JOIN does not support remote cluster indices [{}]",
+                        r.table().index()
+                    );
+                }
+            });
+
+            return new LookupJoin(source, p, right, joinFields);
+        };
     }
 }

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/analysis/AnalyzerTests.java

@@ -2253,24 +2253,6 @@ public void testLookupJoinIndexMode() {
         assertThat(e.getMessage(), containsString("1:25: invalid [test] resolution in lookup mode to an index in [standard] mode"));
     }
 
-    public void testLookupJoinRemoteClusterUnsupported() {
-        assumeTrue("requires LOOKUP JOIN capability", EsqlCapabilities.Cap.JOIN_LOOKUP_V11.isEnabled());
-
-        var remoteIndexResolution = loadMapping("mapping-default.json", "remote:my-index");
-        var lookupResolution = AnalyzerTestUtils.defaultLookupResolution();
-        VerificationException e = expectThrows(
-            VerificationException.class,
-            () -> analyze(
-                "FROM remote:my-index | LOOKUP JOIN languages_lookup ON language_code",
-                AnalyzerTestUtils.analyzer(remoteIndexResolution, lookupResolution)
-            )
-        );
-        assertThat(
-            e.getMessage(),
-            containsString("1:24: LOOKUP JOIN does not support joining with remote cluster indices [remote:my-index]")
-        );
-    }
-
     public void testImplicitCasting() {
         var e = expectThrows(VerificationException.class, () -> analyze("""
              from test | eval x = concat("2024", "-04", "-01") + 1 day