Don't touch Equals

Author: astefan

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/comparison/Equals.java

@@ -27,6 +27,7 @@
 import org.elasticsearch.xpack.esql.querydsl.query.SingleValueQuery;
 
 import java.time.ZoneId;
+import java.util.Collection;
 import java.util.Map;
 
 public class Equals extends EsqlBinaryComparison implements Negatable<EsqlBinaryComparison> {
@@ -139,6 +140,12 @@ public Equals(Source source, Expression left, Expression right, ZoneId zoneId) {
     @Override
     public Translatable translatable(LucenePushdownPredicates pushdownPredicates) {
         if (right() instanceof Literal lit) {
+            // Multi-valued literals are not supported going further. This also makes sure that we are handling multi-valued literals with
+            // a "warning" header, as well (see EqualsKeywordsEvaluator, for example, where lhs and rhs are both dealt with equally when
+            // it comes to multi-value handling).
+            if (lit.value() instanceof Collection<?>) {
+                return Translatable.NO;
+            }
             if (left().dataType() == DataType.TEXT && left() instanceof FieldAttribute fa) {
                 if (pushdownPredicates.canUseEqualityOnSyntheticSourceDelegate(fa, ((BytesRef) lit.value()).utf8ToString())) {
                     return Translatable.YES_BUT_RECHECK_NEGATED;