Refactor a bit more.

src/Processors/QueryPlan/Optimizations/optimizeUseProjections.cpp

@@ -22,6 +22,131 @@
 namespace DB::QueryPlanOptimizations
 {
 
+static QueryPlan::Node * findReadingStep(QueryPlan::Node & node)
+{
+    IQueryPlanStep * step = node.step.get();
+    if (auto * reading = typeid_cast<ReadFromMergeTree *>(step))
+        return &node;
+
+    if (node.children.size() != 1)
+        return nullptr;
+
+    if (typeid_cast<ExpressionStep *>(step) || typeid_cast<FilterStep *>(step))
+        return findReadingStep(*node.children.front());
+
+    return nullptr;
+}
+
+/// This is a common DAG which is a merge of DAGs from Filter and Expression steps chain.
+/// Additionally, for all the Filter steps, we collect filter conditions into filter_nodes.
+/// Flag remove_last_filter_node is set in case if the last step is a Filter step and it should remove filter column.
+struct QueryDAG
+{
+    ActionsDAGPtr dag;
+    ActionsDAG::NodeRawConstPtrs filter_nodes;
+    bool remove_last_filter_node = false;
+
+    bool build(QueryPlan::Node & node);
+
+private:
+    void appendExpression(const ActionsDAGPtr & expression)
+    {
+        if (dag)
+            dag->mergeInplace(std::move(*expression->clone()));
+        else
+            dag = expression->clone();
+    }
+};
+
+bool QueryDAG::build(QueryPlan::Node & node)
+{
+    IQueryPlanStep * step = node.step.get();
+    if (auto * reading = typeid_cast<ReadFromMergeTree *>(step))
+    {
+        if (const auto * prewhere_info = reading->getPrewhereInfo())
+        {
+            if (prewhere_info->row_level_filter)
+            {
+                remove_last_filter_node = false;
+                appendExpression(prewhere_info->row_level_filter);
+                if (const auto * filter_node = dag->tryFindInOutputs(prewhere_info->row_level_column_name))
+                    filter_nodes.push_back(filter_node);
+                else
+                    return false;
+            }
+
+            if (prewhere_info->prewhere_actions)
+            {
+                remove_last_filter_node = prewhere_info->remove_prewhere_column;
+                appendExpression(prewhere_info->prewhere_actions);
+                if (const auto * filter_node = dag->tryFindInOutputs(prewhere_info->prewhere_column_name))
+                    filter_nodes.push_back(filter_node);
+                else
+                    return false;
+            }
+        }
+        return true;
+    }
+
+    if (node.children.size() != 1)
+        return false;
+
+    if (!build(*node.children.front()))
+        return false;
+
+    if (auto * expression = typeid_cast<ExpressionStep *>(step))
+    {
+        const auto & actions = expression->getExpression();
+        if (actions->hasArrayJoin())
+            return false;
+
+        appendExpression(actions);
+        remove_last_filter_node = false;
+        return true;
+    }
+
+    if (auto * filter = typeid_cast<FilterStep *>(step))
+    {
+        const auto & actions = filter->getExpression();
+        if (actions->hasArrayJoin())
+            return false;
+
+        appendExpression(actions);
+        remove_last_filter_node = filter->removesFilterColumn();
+        const auto * filter_expression = dag->tryFindInOutputs(filter->getFilterColumnName());
+        if (!filter_expression)
+            return false;
+
+        filter_nodes.push_back(filter_expression);
+        return true;
+    }
+
+    return false;
+}
+
+bool canUseProjectionForReadingStep(ReadFromMergeTree * reading)
+{
+    /// Probably some projection already was applied.
+    if (reading->hasAnalyzedResult())
+        return false;
+
+    if (reading->isQueryWithFinal())
+        return false;
+
+    if (reading->isQueryWithSampling())
+        return false;
+
+    if (reading->isParallelReadingEnabled())
+        return false;
+
+    // Currently projection don't support deduplication when moving parts between shards.
+    if (reading->getContext()->getSettingsRef().allow_experimental_query_deduplication)
+        return false;
+
+    return true;
+}
+
+
 /// Required analysis info from aggregate projection.
 struct AggregateProjectionInfo
 {
@@ -255,17 +380,120 @@ bool areAggregatesMatch(
     return true;
 }
 
+struct AggregateQueryDAG
+{
+    ActionsDAGPtr dag;
+    const ActionsDAG::Node * filter_node = nullptr;
+
+    bool build(QueryPlan::Node & node)
+    {
+        QueryDAG query;
+        if (!query.build(node))
+            return false;
+
+        dag = std::move(query.dag);
+        auto filter_nodes = std::move(query.filter_nodes);
+
+        if (!filter_nodes.empty())
+        {
+            filter_node = filter_nodes.front();
+            if (filter_nodes.size() > 1)
+            {
+                FunctionOverloadResolverPtr func_builder_and =
+                    std::make_unique<FunctionToOverloadResolverAdaptor>(
+                        std::make_shared<FunctionAnd>());
+
+                filter_node = &dag->addFunction(func_builder_and, std::move(filter_nodes), {});
+            }
+
+            dag->getOutputs().push_back(filter_node);
+        }
+
+        return true;
+    }
+};
+
+struct NormalQueryDAG
+{
+    ActionsDAGPtr dag;
+    bool need_remove_column = false;
+    const ActionsDAG::Node * filter_node = nullptr;
+
+    bool build(QueryPlan::Node & node)
+    {
+        QueryDAG query;
+        if (!query.build(node))
+            return false;
+
+        dag = std::move(query.dag);
+        auto filter_nodes = std::move(query.filter_nodes);
+        need_remove_column = query.remove_last_filter_node;
+
+        if (!filter_nodes.empty())
+        {
+            auto & outputs = dag->getOutputs();
+            filter_node = filter_nodes.back();
+
+            if (filter_nodes.size() > 1)
+            {
+                /// Add a conjunction of all the filters.
+                if (need_remove_column)
+                {
+                    /// Last filter column is not needed; remove it right here
+                    size_t pos = 0;
+                    while (pos < outputs.size() && outputs[pos] != filter_node)
+                        ++pos;
+
+                    if (pos < outputs.size())
+                        outputs.erase(outputs.begin() + pos);
+                }
+                else
+                {
+                    /// Last filter is needed; we must replace it to constant 1,
+                    /// As well as FilterStep does to make a compatible header.
+                    for (auto & output : outputs)
+                    {
+                        if (output == filter_node)
+                        {
+                            ColumnWithTypeAndName col;
+                            col.name = filter_node->result_name;
+                            col.type = filter_node->result_type;
+                            col.column = col.type->createColumnConst(1, 1);
+                            output = &dag->addColumn(std::move(col));
+                        }
+                    }
+                }
+
+                FunctionOverloadResolverPtr func_builder_and =
+                    std::make_unique<FunctionToOverloadResolverAdaptor>(
+                        std::make_shared<FunctionAnd>());
+
+                filter_node = &dag->addFunction(func_builder_and, std::move(filter_nodes), {});
+                outputs.insert(outputs.begin(), filter_node);
+                need_remove_column = true;
+            }
+        }
+
+        if (dag)
+        {
+            dag->removeUnusedActions();
+            // LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Header {}, Query DAG: {}", header.dumpStructure(), dag->dumpDAG());
+        }
+
+        return true;
+    }
+};
+
 ActionsDAGPtr analyzeAggregateProjection(
     const AggregateProjectionInfo & info,
-    const ActionsDAG & query_dag,
-    const ActionsDAG::Node * filter_node,
+    const AggregateQueryDAG & query,
     const Names & keys,
     const AggregateDescriptions & aggregates)
 {
-    auto query_index = buildDAGIndex(query_dag);
+    auto query_index = buildDAGIndex(*query.dag);
     auto proj_index = buildDAGIndex(*info.before_aggregation);
 
-    MatchedTrees::Matches matches = matchTrees(*info.before_aggregation, query_dag);
+    MatchedTrees::Matches matches = matchTrees(*info.before_aggregation, *query.dag);
 
     // for (const auto & [node, match] : matches)
     // {
@@ -298,8 +526,8 @@ ActionsDAGPtr analyzeAggregateProjection(
         /// We need to add filter column to keys set.
         /// It should be computable from projection keys.
         /// It will be removed in FilterStep.
-        if (filter_node)
-            query_key_nodes.push_back(filter_node);
+        if (query.filter_node)
+            query_key_nodes.push_back(query.filter_node);
 
         for (const auto & key : keys)
         {
@@ -362,7 +590,7 @@ ActionsDAGPtr analyzeAggregateProjection(
             /// Not a match and there is no matched child.
             if (frame.node->type == ActionsDAG::ActionType::INPUT)
             {
-                LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Cannot find match for {}", frame.node->result_name);
+                // LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Cannot find match for {}", frame.node->result_name);
                 return {};
             }
 
@@ -374,7 +602,7 @@ ActionsDAGPtr analyzeAggregateProjection(
 
     // LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Folding actions by projection");
 
-    auto proj_dag = query_dag.foldActionsByProjection(new_inputs, query_key_nodes);
+    auto proj_dag = query.dag->foldActionsByProjection(new_inputs, query_key_nodes);
 
     /// Just add all the aggregates to dag inputs.
     auto & proj_dag_outputs =  proj_dag->getOutputs();
@@ -384,125 +612,6 @@ ActionsDAGPtr analyzeAggregateProjection(
     return proj_dag;
 }
 
-static QueryPlan::Node * findReadingStep(QueryPlan::Node & node)
-{
-    IQueryPlanStep * step = node.step.get();
-    if (auto * reading = typeid_cast<ReadFromMergeTree *>(step))
-        return &node;
-
-    if (node.children.size() != 1)
-        return nullptr;
-
-    if (typeid_cast<ExpressionStep *>(step) || typeid_cast<FilterStep *>(step))
-        return findReadingStep(*node.children.front());
-
-    return nullptr;
-}
-
-static void appendExpression(ActionsDAGPtr & dag, const ActionsDAGPtr & expression)
-{
-    if (dag)
-        dag->mergeInplace(std::move(*expression->clone()));
-    else
-        dag = expression->clone();
-}
-
-
-/// This function builds a common DAG which is a merge of DAGs from Filter and Expression steps chain.
-/// Additionally, for all the Filter steps, we collect filter conditions into filter_nodes.
-/// Flag need_remove_column is set in case if the last step is a Filter step and it should remove filter column.
-static bool buildQueryDAG(
-    QueryPlan::Node & node,
-    ActionsDAGPtr & dag,
-    ActionsDAG::NodeRawConstPtrs & filter_nodes,
-    bool & need_remove_column)
-{
-    IQueryPlanStep * step = node.step.get();
-    if (auto * reading = typeid_cast<ReadFromMergeTree *>(step))
-    {
-        if (const auto * prewhere_info = reading->getPrewhereInfo())
-        {
-            if (prewhere_info->row_level_filter)
-            {
-                need_remove_column = false;
-                appendExpression(dag, prewhere_info->row_level_filter);
-                if (const auto * filter_node = dag->tryFindInOutputs(prewhere_info->row_level_column_name))
-                    filter_nodes.push_back(filter_node);
-                else
-                    return false;
-            }
-
-            if (prewhere_info->prewhere_actions)
-            {
-                need_remove_column = prewhere_info->remove_prewhere_column;
-                appendExpression(dag, prewhere_info->prewhere_actions);
-                if (const auto * filter_node = dag->tryFindInOutputs(prewhere_info->prewhere_column_name))
-                    filter_nodes.push_back(filter_node);
-                else
-                    return false;
-            }
-        }
-        return true;
-    }
-
-    if (node.children.size() != 1)
-        return false;
-
-    if (!buildQueryDAG(*node.children.front(), dag, filter_nodes, need_remove_column))
-        return false;
-
-    if (auto * expression = typeid_cast<ExpressionStep *>(step))
-    {
-        const auto & actions = expression->getExpression();
-        if (actions->hasArrayJoin())
-            return false;
-
-        appendExpression(dag, actions);
-        need_remove_column = false;
-        return true;
-    }
-
-    if (auto * filter = typeid_cast<FilterStep *>(step))
-    {
-        const auto & actions = filter->getExpression();
-        if (actions->hasArrayJoin())
-            return false;
-
-        appendExpression(dag, actions);
-        need_remove_column = filter->removesFilterColumn();
-        const auto * filter_expression = dag->tryFindInOutputs(filter->getFilterColumnName());
-        if (!filter_expression)
-            return false;
-
-        filter_nodes.push_back(filter_expression);
-        return true;
-    }
-
-    return false;
-}
-
-bool canUseProjectionForReadingStep(ReadFromMergeTree * reading)
-{
-    /// Probably some projection already was applied.
-    if (reading->hasAnalyzedResult())
-        return false;
-
-    if (reading->isQueryWithFinal())
-        return false;
-
-    if (reading->isQueryWithSampling())
-        return false;
-
-    if (reading->isParallelReadingEnabled())
-        return false;
-
-    // Currently projection don't support deduplication when moving parts between shards.
-    if (reading->getContext()->getSettingsRef().allow_experimental_query_deduplication)
-        return false;
-
-    return true;
-}
-
 struct MinMaxProjectionCandidate
 {
     AggregateProjectionCandidate candidate;
@@ -514,6 +623,8 @@ struct AggregateProjectionCandidates
 {
     std::vector<AggregateProjectionCandidate> real;
     std::optional<MinMaxProjectionCandidate> minmax_projection;
+
+    /// This flag means that DAG for projection candidate should be used in FilterStep.
     bool has_filter = false;
 };
 
@@ -548,30 +659,13 @@ AggregateProjectionCandidates getAggregateProjectionCandidates(
 
     // LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Has agg projection");
 
-    ActionsDAGPtr dag;
-    bool need_remove_column = false; // not used here
-    ActionsDAG::NodeRawConstPtrs filter_nodes;
-    if (!buildQueryDAG(*node.children.front(), dag, filter_nodes, need_remove_column))
+    AggregateQueryDAG dag;
+    if (!dag.build(*node.children.front()))
         return candidates;
 
-    // LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Query DAG: {}", dag->dumpDAG());
+    LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Query DAG: {}", dag.dag->dumpDAG());
 
-    const ActionsDAG::Node * filter_node = nullptr;
-    if (!filter_nodes.empty())
-    {
-        filter_node = filter_nodes.front();
-        if (filter_nodes.size() > 1)
-        {
-            FunctionOverloadResolverPtr func_builder_and =
-                std::make_unique<FunctionToOverloadResolverAdaptor>(
-                    std::make_shared<FunctionAnd>());
-
-            filter_node = &dag->addFunction(func_builder_and, std::move(filter_nodes), {});
-        }
-
-        dag->getOutputs().push_back(filter_node);
-    }
-    candidates.has_filter = filter_node;
+    candidates.has_filter = dag.filter_node;
 
     if (can_use_minmax_projection)
     {
@@ -579,7 +673,7 @@ AggregateProjectionCandidates getAggregateProjectionCandidates(
         // LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Try projection {}", projection->name);
         auto info = getAggregatingProjectionInfo(*projection, context, metadata, key_virtual_columns);
         // LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Projection DAG {}", info.before_aggregation->dumpDAG());
-        if (auto proj_dag = analyzeAggregateProjection(info, *dag, filter_node, keys, aggregates))
+        if (auto proj_dag = analyzeAggregateProjection(info, dag, keys, aggregates))
         {
             // LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Projection analyzed DAG {}", proj_dag->dumpDAG());
             AggregateProjectionCandidate candidate{.info = std::move(info), .dag = std::move(proj_dag)};
@@ -588,7 +682,7 @@ AggregateProjectionCandidates getAggregateProjectionCandidates(
             auto block = reading.getMergeTreeData().getMinMaxCountProjectionBlock(
                 metadata,
                 candidate.dag->getRequiredColumnsNames(),
-                filter_node != nullptr,
+                dag.filter_node != nullptr,
                 query_info,
                 parts,
                 minmax_projection_normal_parts,
@@ -615,7 +709,7 @@ AggregateProjectionCandidates getAggregateProjectionCandidates(
             // LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Try projection {}", projection->name);
             auto info = getAggregatingProjectionInfo(*projection, context, metadata, key_virtual_columns);
             // LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Projection DAG {}", info.before_aggregation->dumpDAG());
-            if (auto proj_dag = analyzeAggregateProjection(info, *dag, filter_node, keys, aggregates))
+            if (auto proj_dag = analyzeAggregateProjection(info, dag, keys, aggregates))
             {
                 // LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Projection analyzed DAG {}", proj_dag->dumpDAG());
                 AggregateProjectionCandidate candidate{.info = std::move(info), .dag = std::move(proj_dag)};
@@ -823,6 +917,40 @@ bool optimizeUseAggProjections(QueryPlan::Node & node, QueryPlan::Nodes & nodes)
     return true;
 }
 
+ActionsDAGPtr makeMaterializingDAG(const Block & proj_header, const Block main_header)
+{
+    /// Materialize constants in case we don't have it in output header.
+    /// This may happen e.g. if we have PREWHERE.
+
+    size_t num_columns = main_header.columns();
+    /// This is a error; will have block structure mismatch later.
+    if (proj_header.columns() != num_columns)
+        return nullptr;
+
+    std::vector<size_t> const_positions;
+    for (size_t i = 0; i < num_columns; ++i)
+    {
+        auto col_proj = proj_header.getByPosition(i).column;
+        auto col_main = main_header.getByPosition(i).column;
+        bool is_proj_const = col_proj && isColumnConst(*col_proj);
+        bool is_main_proj = col_main && isColumnConst(*col_main);
+        if (is_proj_const && !is_main_proj)
+            const_positions.push_back(i);
+    }
+
+    if (const_positions.empty())
+        return nullptr;
+
+    ActionsDAGPtr dag = std::make_unique<ActionsDAG>(proj_header.getColumnsWithTypeAndName());
+    for (auto pos : const_positions)
+    {
+        auto & output = dag->getOutputs()[pos];
+        output = &dag->materializeNode(*output);
+    }
+
+    return dag;
+}
+
 
 bool optimizeUseNormalProjections(Stack & stack, QueryPlan::Nodes & nodes)
 {
@@ -863,66 +991,15 @@ bool optimizeUseNormalProjections(Stack & stack, QueryPlan::Nodes & nodes)
     if (normal_projections.empty())
         return false;
 
-    ActionsDAGPtr dag;
-    ActionsDAG::NodeRawConstPtrs filter_nodes;
-    bool need_remove_column = false;
-    if (!buildQueryDAG(*iter->node->children.front(), dag, filter_nodes, need_remove_column))
-        return false;
-
-    const ActionsDAG::Node * filter_node = nullptr;
-    if (!filter_nodes.empty())
+    NormalQueryDAG query;
     {
-        auto & outputs = dag->getOutputs();
-        filter_node = filter_nodes.back();
-
-        if (filter_nodes.size() > 1)
-        {
-            if (need_remove_column)
-            {
-                size_t pos = 0;
-                while (pos < outputs.size() && outputs[pos] != filter_node)
-                    ++pos;
-
-                if (pos < outputs.size())
-                    outputs.erase(outputs.begin() + pos);
-            }
-            else
-            {
-                for (auto & output : outputs)
-                {
-                    if (output == filter_node)
-                    {
-                        ColumnWithTypeAndName col;
-                        col.name = filter_node->result_name;
-                        col.type = filter_node->result_type;
-                        col.column = col.type->createColumnConst(1, 1);
-                        output = &dag->addColumn(std::move(col));
-                    }
-                }
-            }
-
-            FunctionOverloadResolverPtr func_builder_and =
-                std::make_unique<FunctionToOverloadResolverAdaptor>(
-                    std::make_shared<FunctionAnd>());
-
-            filter_node = &dag->addFunction(func_builder_and, std::move(filter_nodes), {});
-            outputs.insert(outputs.begin(), filter_node);
-            need_remove_column = true;
-        }
-        // else if (!need_remove_column)
-        //     outputs.insert(outputs.begin(), filter_node);
-    }
-
-    if (dag)
-    {
-        dag->removeUnusedActions();
-        LOG_TRACE(&Poco::Logger::get("optimizeUseProjections"), "Query DAG: {}", dag->dumpDAG());
+        if (!query.build(*iter->node->children.front()))
+            return false;
     }
 
     std::list<NormalProjectionCandidate> candidates;
     NormalProjectionCandidate * best_candidate = nullptr;
 
-    //const Block & header = frame.node->step->getOutputStream().header;
     const Names & required_columns = reading->getRealColumnNames();
     const auto & parts = reading->getParts();
     const auto & query_info = reading->getQueryInfo();
@@ -972,8 +1049,8 @@ bool optimizeUseNormalProjections(Stack & stack, QueryPlan::Nodes & nodes)
             continue;
 
         ActionDAGNodes added_filter_nodes;
-        if (filter_node)
-            added_filter_nodes.nodes.push_back(filter_node);
+        if (query.filter_node)
+            added_filter_nodes.nodes.push_back(query.filter_node);
 
         auto projection_result_ptr = reader.estimateNumMarksToRead(
             std::move(projection_parts),
@@ -1059,25 +1136,22 @@ bool optimizeUseNormalProjections(Stack & stack, QueryPlan::Nodes & nodes)
     auto & projection_reading_node = nodes.emplace_back(QueryPlan::Node{.step = std::move(projection_reading)});
     auto * next_node = &projection_reading_node;
 
-    if (dag)
+    if (query.dag)
     {
         auto & expr_or_filter_node = nodes.emplace_back();
 
-        if (filter_node)
+        if (query.filter_node)
         {
-            //std::cerr << "======== " << projection_reading_node.step->getOutputStream().header.dumpStructure();
             expr_or_filter_node.step = std::make_unique<FilterStep>(
                 projection_reading_node.step->getOutputStream(),
-                dag,
-                filter_node->result_name,
-                need_remove_column);
-
-            //std::cerr << "======2= " << expr_or_filter_node.step->getOutputStream().header.dumpStructure();
+                query.dag,
+                query.filter_node->result_name,
+                query.need_remove_column);
         }
         else
             expr_or_filter_node.step = std::make_unique<ExpressionStep>(
                 projection_reading_node.step->getOutputStream(),
-                dag);
+                query.dag);
 
         expr_or_filter_node.children.push_back(&projection_reading_node);
         next_node = &expr_or_filter_node;
@@ -1087,31 +1161,26 @@ bool optimizeUseNormalProjections(Stack & stack, QueryPlan::Nodes & nodes)
     {
         /// All parts are taken from projection
         iter->node->children.front() = next_node;
-
-        //optimizeAggregationInOrder(node, nodes);
     }
     else
     {
         const auto & main_stream = iter->node->children.front()->step->getOutputStream();
         const auto * proj_stream = &next_node->step->getOutputStream();
 
-        if (!blocksHaveEqualStructure(proj_stream->header, main_stream.header))
+        if (auto materializing = makeMaterializingDAG(proj_stream->header, main_stream.header))
         {
+            // auto convert_actions_dag = ActionsDAG::makeConvertingActions(
+            //     proj_stream->header.getColumnsWithTypeAndName(),
+            //     main_stream.header.getColumnsWithTypeAndName(),
+            //     ActionsDAG::MatchColumnsMode::Name,
+            //     true);
 
-            //std::cerr << "======3= " << next_node->step->getOutputStream().header.dumpStructure();
-            auto convert_actions_dag = ActionsDAG::makeConvertingActions(
-                proj_stream->header.getColumnsWithTypeAndName(),
-                main_stream.header.getColumnsWithTypeAndName(),
-                ActionsDAG::MatchColumnsMode::Name,
-                true);
-
-            auto converting = std::make_unique<ExpressionStep>(*proj_stream, convert_actions_dag);
+            auto converting = std::make_unique<ExpressionStep>(*proj_stream, materializing);
             proj_stream = &converting->getOutputStream();
             auto & expr_node = nodes.emplace_back();
             expr_node.step = std::move(converting);
             expr_node.children.push_back(next_node);
             next_node = &expr_node;
-            //std::cerr << "======4= " << next_node->step->getOutputStream().header.dumpStructure();
         }
 
         auto & union_node = nodes.emplace_back();