add basic cluster string validation

Author: idegtiarenko

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

@@ -13,6 +13,7 @@
 import org.elasticsearch.cluster.metadata.MetadataCreateIndexService;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.indices.InvalidIndexNameException;
+import org.elasticsearch.transport.RemoteClusterService;
 import org.elasticsearch.xpack.esql.core.util.Holder;
 import org.elasticsearch.xpack.esql.parser.EsqlBaseParser.IdentifierContext;
 import org.elasticsearch.xpack.esql.parser.EsqlBaseParser.IndexStringContext;
@@ -82,12 +83,20 @@ public String visitIndexPattern(List<EsqlBaseParser.IndexPatternContext> ctx) {
             if (clusterString == null) {
                 hasSeenStar.set(indexPattern.contains(WILDCARD) || hasSeenStar.get());
                 validateIndexPattern(indexPattern, c, hasSeenStar.get());
+            } else {
+                validateClusterString(clusterString, c);
             }
             patterns.add(clusterString != null ? clusterString + REMOTE_CLUSTER_INDEX_SEPARATOR + indexPattern : indexPattern);
         });
         return Strings.collectionToDelimitedString(patterns, ",");
     }
 
+    protected static void validateClusterString(String clusterString, EsqlBaseParser.IndexPatternContext ctx) {
+        if (clusterString.indexOf(RemoteClusterService.REMOTE_CLUSTER_INDEX_SEPARATOR) != -1) {
+            throw new ParsingException(source(ctx), "cluster string [{}] must not contain ':'", clusterString);
+        }
+    }
+
     private static void validateIndexPattern(String indexPattern, EsqlBaseParser.IndexPatternContext ctx, boolean hasSeenStar) {
         // multiple index names can be in the same double quote, e.g. indexPattern = "idx1, *, -idx2"
         String[] indices = indexPattern.split(",");

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/parser/StatementParserTests.java

@@ -615,7 +615,7 @@ private void clustersAndIndices(String command, String indexString1, String inde
         );
     }
 
-    public void testValidQuotingFromIndexPattern() {
+    public void testValidFromIndexPattern() {
         var patterns = randomList(1, 5, () -> {
             String pattern = randomIndexIdentifier();// index or alias
             if (randomBoolean()) {// pattern
@@ -664,6 +664,11 @@ private static char randomCharacterFrom(String str) {
         return str.charAt(randomInt(str.length() - 1));
     }
 
+    public void testInvalidFromIndexPattern() {
+        expectError("FROM \"remote:\":index", "line 1:6: cluster string [remote:] must not contain ':'");
+        expectError("FROM \"remote:invalid\":index", "line 1:6: cluster string [remote:invalid] must not contain ':'");
+    }
+
     public void testInvalidQuotingAsFromIndexPattern() {
         expectError("FROM \"foo", ": token recognition error at: '\"foo'");
         expectError("FROM \"foo | LIMIT 1", ": token recognition error at: '\"foo | LIMIT 1'");