ES|QL: Check if cluster aliases and index patterns are valid before executing query

docs/changelog/122497.yaml

@@ -0,0 +1,5 @@
+pr: 122497
+summary: Check if index patterns conform to valid format before validation
+area: CCS
+type: bug
+issues: []

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

@@ -78,6 +78,15 @@ public String visitIndexPattern(List<EsqlBaseParser.IndexPatternContext> ctx) {
         ctx.forEach(c -> {
             String indexPattern = visitIndexString(c.indexString());
             String clusterString = visitClusterString(c.clusterString());
+            // 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.
+            // Should clusterString be non-null, validateClusterString() handles the required validation. So for now, look only at
+            // the indexPattern.
+            var maxSeparators = clusterString == null ? 1 : 0;
+            if (patternExceedsMaxIndexSeparators(indexPattern, maxSeparators)) {
+                throw new ParsingException(source(c), "Unexpected index separator 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) {
@@ -138,4 +147,20 @@ private static void validateIndexPattern(String indexPattern, EsqlBaseParser.Ind
     private static String removeExclusion(String indexPattern) {
         return indexPattern.charAt(0) == EXCLUSION.charAt(0) ? indexPattern.substring(1) : indexPattern;
     }
+
+    private static boolean patternExceedsMaxIndexSeparators(String pattern, int maxAllowedSeparators) {
+        int seperatorsCount = 0;
+        boolean inDateTime = false;
+        for (char ch : pattern.toCharArray()) {
+            if (ch == '<') {
+                inDateTime = true;
+            } else if (ch == '>') {
+                inDateTime = false;
+            } else if (ch == REMOTE_CLUSTER_INDEX_SEPARATOR && inDateTime == false) {
+                seperatorsCount++;
+            }
+        }
+
+        return seperatorsCount > maxAllowedSeparators;
+    }
 }

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\"", "Unexpected index separator in index patter");
+        expectError("FROM \"remote:foo:bar:baz\"", "Unexpected index separator in index patter");
     }
 
     public void testInvalidQuotingAsMetricsIndexPattern() {