Allow FTFs in WHERE clauses but not in grouping clauses

Author: carlosdelest

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/fulltext/FullTextFunction.java

@@ -32,7 +32,6 @@
 import org.elasticsearch.xpack.esql.core.type.DataType;
 import org.elasticsearch.xpack.esql.core.type.DataTypeConverter;
 import org.elasticsearch.xpack.esql.evaluator.mapper.EvaluatorMapper;
-import org.elasticsearch.xpack.esql.expression.function.aggregate.FilteredExpression;
 import org.elasticsearch.xpack.esql.expression.predicate.logical.BinaryLogic;
 import org.elasticsearch.xpack.esql.expression.predicate.logical.Not;
 import org.elasticsearch.xpack.esql.optimizer.rules.physical.local.LucenePushdownPredicates;
@@ -228,7 +227,7 @@ private static void checkFullTextQueryFunctions(LogicalPlan plan, Failures failu
             );
             checkFullTextFunctionsParents(condition, failures);
         } else if (plan instanceof Aggregate agg) {
-            agg.forEachExpression(exp -> checkFullTextFunctionsInAggs(exp, failures));
+            checkFullTextFunctionsInAggs(agg, failures);
         } else {
             plan.forEachExpression(FullTextFunction.class, ftf -> {
                 failures.add(
@@ -238,19 +237,16 @@ private static void checkFullTextQueryFunctions(LogicalPlan plan, Failures failu
         }
     }
 
-    private static void checkFullTextFunctionsInAggs(Expression expression, Failures failures) {
-        if (expression instanceof FilteredExpression) {
-            return;
-        }
-        for (Expression child : expression.children()) {
-            if (child instanceof FullTextFunction ftf) {
-                failures.add(
-                    fail(ftf, "[{}] {} is only supported in WHERE and STATS ... WHERE commands", ftf.functionName(), ftf.functionType())
-                );
-                return;
-            }
-            checkFullTextFunctionsInAggs(child, failures);
-        }
+    private static void checkFullTextFunctionsInAggs(Aggregate agg, Failures failures) {
+        agg.groupings().forEach(exp -> {
+            exp.forEachDown(e -> {
+                if (e instanceof FullTextFunction ftf) {
+                    failures.add(
+                        fail(ftf, "[{}] {} is only supported in WHERE and STATS ... WHERE commands", ftf.functionName(), ftf.functionType())
+                    );
+                }
+            });
+        });
     }
 
     /**