Restrict remote LOOKUP JOIN after FORK

Author: smalyshev

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/plan/logical/Enrich.java

@@ -314,6 +314,7 @@ private static void checkForPlansForbiddenBeforeRemoteEnrich(Enrich enrich, Fail
         boolean[] aggregate = { false };
         boolean[] coordinatorOnlyEnrich = { false };
         boolean[] lookupJoin = { false };
+        boolean[] fork = { false };
 
         enrich.forEachUp(LogicalPlan.class, u -> {
             if (u instanceof Aggregate) {
@@ -322,6 +323,8 @@ private static void checkForPlansForbiddenBeforeRemoteEnrich(Enrich enrich, Fail
                 coordinatorOnlyEnrich[0] = true;
             } else if (u instanceof LookupJoin) {
                 lookupJoin[0] = true;
+            } else if (u instanceof Fork) {
+                fork[0] = true;
             }
         });
 
@@ -334,5 +337,8 @@ private static void checkForPlansForbiddenBeforeRemoteEnrich(Enrich enrich, Fail
         if (lookupJoin[0]) {
             failures.add(fail(enrich, "ENRICH with remote policy can't be executed after LOOKUP JOIN"));
         }
+        if (fork[0]) {
+            failures.add(fail(enrich, "ENRICH with remote policy can't be executed after FORK"));
+        }
     }
 }

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

@@ -2457,6 +2457,14 @@ public void testRemoteEnrichAfterCoordinatorOnlyPlans() {
             | ENRICH _remote:languages ON language_code
             """, analyzer);
         assertThat(err, containsString("7:3: ENRICH with remote policy can't be executed after another ENRICH with coordinator policy"));
+
+        err = error("""
+            FROM test
+            | FORK (WHERE languages == 1) (WHERE languages == 2)
+            | EVAL language_code = languages
+            | ENRICH _remote:languages ON language_code
+            """, analyzer);
+        assertThat(err, containsString("4:3: ENRICH with remote policy can't be executed after FORK"));
     }
 
     private void checkFullTextFunctionsInStats(String functionInvocation) {