Fix alias id when drop all aggregates

docs/changelog/135247.yaml

@@ -0,0 +1,5 @@
+pr: 135247
+summary: Fix alias id when drop all aggregates
+area: ES|QL
+type: bug
+issues: []

x-pack/plugin/esql/qa/testFixtures/src/main/resources/eval.csv-spec

@@ -788,3 +788,20 @@ from firewall_logs,threat_list,airports
 dsjbDWegyVkg:boolean    | name:integer  | nhIWDevxEtU:null  | iPIbTFddDK:integer    | rUvqtgSl:integer
 false                   | 1             | null              | 1                     | 1
 ;
+
+evalAfterGroupingUsingSameName6
+required_capability: fix_alias_id_when_drop_all_aggregates
+from employees
+| stats sum=sum(salary) by last_name, year = bucket(birth_date, 1 year)
+| DROP sum
+| DROP last_name
+| eval year = 12
+| LIMIT 4
+;
+
+year:integer
+12
+12
+12
+12
+;

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -1538,6 +1538,8 @@ public enum Cap {
          */
         TS_COMMAND_V0(),
 
+        FIX_ALIAS_ID_WHEN_DROP_ALL_AGGREGATES
+
         ;
 
         private final boolean enabled;

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/logical/PruneColumns.java

@@ -115,7 +115,7 @@ private static LogicalPlan pruneColumnsInAggregate(Aggregate aggregate, Attribut
                 // Aggs cannot produce pages with 0 columns, so retain one grouping.
                 Attribute attribute = Expressions.attribute(aggregate.groupings().getFirst());
                 NamedExpression firstAggregate = aggregate.aggregates().getFirst();
-                remaining = List.of(new Alias(firstAggregate.source(), firstAggregate.name(), attribute, firstAggregate.id()));
+                remaining = List.of(new Alias(firstAggregate.source(), firstAggregate.name(), attribute, attribute.id()));
                 p = aggregate.with(aggregate.groupings(), remaining);
             }
         } else {

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/optimizer/LogicalPlanOptimizerTests.java

@@ -291,6 +291,7 @@ public void testEmptyProjectInStatWithGroupAndEval() {
 
         assertThat(Expressions.names(agg.groupings()), contains("emp_no"));
         assertThat(Expressions.names(agg.aggregates()), contains("c"));
+        assertThat(agg.aggregates().get(0).id(), equalTo(Expressions.attribute(agg.groupings().get(0)).id()));
 
         var exprs = eval.fields();
         assertThat(exprs.size(), equalTo(1));