Check if index patterns conform to valid format before validation

Author: pawankartik-elastic

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

@@ -78,6 +78,13 @@ public String visitIndexPattern(List<EsqlBaseParser.IndexPatternContext> ctx) {
         ctx.forEach(c -> {
             String indexPattern = visitIndexString(c.indexString());
             String clusterString = visitClusterString(c.clusterString());
+            String assembledName = clusterString != null ? clusterString + REMOTE_CLUSTER_INDEX_SEPARATOR + indexPattern : indexPattern;
+            // At this point, we run 2 kinds of checks. The first check is to ensure that this string adheres to the valid
+            // pattern format. The second check is to ensure that the parts of this string, i.e. the remote name, cluster name, and
+            // other aspects of them are valid. There's no point in running the second check if the first one fails.
+            if (assembledName.codePoints().filter(ch -> ch == REMOTE_CLUSTER_INDEX_SEPARATOR).count() > 1) {
+                throw new ParsingException(source(c), "More than 1 occurrence of index separator found in index pattern");
+            }
             // skip validating index on remote cluster, because the behavior of remote cluster is not consistent with local cluster
             // For example, invalid#index is an invalid index name, however FROM *:invalid#index does not return an error
             if (clusterString == null) {
@@ -86,7 +93,7 @@ public String visitIndexPattern(List<EsqlBaseParser.IndexPatternContext> ctx) {
             } else {
                 validateClusterString(clusterString, c);
             }
-            patterns.add(clusterString != null ? clusterString + REMOTE_CLUSTER_INDEX_SEPARATOR + indexPattern : indexPattern);
+            patterns.add(assembledName);
         });
         return Strings.collectionToDelimitedString(patterns, ",");
     }

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

@@ -644,6 +644,8 @@ public void testInvalidQuotingAsFromIndexPattern() {
 
         expectError("FROM \"\"\"foo\"\"\"bar\"\"\"", ": mismatched input 'bar' expecting {<EOF>, '|', ',', 'metadata'}");
         expectError("FROM \"\"\"foo\"\"\"\"\"\"bar\"\"\"", ": mismatched input '\"bar\"' expecting {<EOF>, '|', ',', 'metadata'}");
+        expectError("FROM remote:\"foo:bar\"", "More than 1 occurrence of index separator found in index pattern");
+        expectError("FROM \"remote:foo:bar:baz\"", "More than 1 occurrence of index separator found in index pattern");
     }
 
     public void testInvalidQuotingAsMetricsIndexPattern() {