Add ToDouble conversion and projection for AcrossSeriesAggregate output (#138655)

Author: felixbarny

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

@@ -38,6 +38,7 @@
 import org.elasticsearch.xpack.esql.plan.logical.Eval;
 import org.elasticsearch.xpack.esql.plan.logical.Filter;
 import org.elasticsearch.xpack.esql.plan.logical.LogicalPlan;
+import org.elasticsearch.xpack.esql.plan.logical.Project;
 import org.elasticsearch.xpack.esql.plan.logical.TimeSeriesAggregate;
 import org.elasticsearch.xpack.esql.plan.logical.promql.AcrossSeriesAggregate;
 import org.elasticsearch.xpack.esql.plan.logical.promql.PlaceholderRelation;
@@ -185,7 +186,26 @@ private static MapResult mapFunction(PromqlCommand promqlCommand, PromqlFunction
 
             LogicalPlan p = childResult.plan;
             p = new Eval(stepBucket.source(), p, List.of(stepBucket));
-            p = new TimeSeriesAggregate(acrossAggregate.source(), p, groupings, aggs, null);
+            TimeSeriesAggregate tsAggregate = new TimeSeriesAggregate(acrossAggregate.source(), p, groupings, aggs, null);
+            p = tsAggregate;
+            // ToDouble conversion of the metric using an eval to ensure a consistent output type
+            Alias convertedValue = new Alias(
+                acrossAggregate.source(),
+                acrossAggregate.sourceText(),
+                new ToDouble(acrossAggregate.source(), p.output().getFirst().toAttribute()),
+                acrossAggregate.valueId()
+            );
+            p = new Eval(acrossAggregate.source(), p, List.of(convertedValue));
+            // Project to maintain the correct output order, as declared in AcrossSeriesAggregate#output:
+            // [value, step, ...groupings]
+            List<NamedExpression> projections = new ArrayList<>();
+            projections.add(convertedValue.toAttribute());
+            List<Attribute> output = tsAggregate.output();
+            for (int i = 1; i < output.size(); i++) {
+                projections.add(output.get(i));
+            }
+            p = new Project(acrossAggregate.source(), p, projections);
+
             result = new MapResult(p, extras);
         } else {
             throw new QlIllegalArgumentException("Unsupported PromQL function call: {}", functionCall);
@@ -205,13 +225,11 @@ private static void initAggregatesAndGroupings(
         Function esqlFunction = PromqlFunctionRegistry.INSTANCE.buildEsqlFunction(
             acrossAggregate.functionName(),
             acrossAggregate.source(),
-            // to double conversion of the metric to ensure a consistent output type
-            // TODO it's probably more efficient to wrap the function in the ToDouble
-            // but for some reason this doesn't work if you have an inner and outer aggregation
-            List.of(new ToDouble(target.source(), target))
+            List.of(target)
         );
 
-        aggs.add(new Alias(acrossAggregate.source(), acrossAggregate.sourceText(), esqlFunction, acrossAggregate.valueId()));
+        Alias value = new Alias(acrossAggregate.source(), acrossAggregate.sourceText(), esqlFunction);
+        aggs.add(value);
 
         // timestamp/step
         aggs.add(stepBucket);