Add infrastructure for asking outputs for their requirements

Outputs are now able to set the requirements they have based on their
configuration. The requirements are queried and communicated to the
middle which can change its configuration based on that.

Author: joto

src/middle.hpp

@@ -18,6 +18,7 @@
 #include "thread-pool.hpp"
 
 class options_t;
+struct output_requirements;
 
 /**
  * Interface for returning information about raw OSM input data from a cache.
@@ -107,6 +108,8 @@ struct middle_t
     virtual idlist_t get_rels_by_way(osmid_t) { return {}; }
 
     virtual std::shared_ptr<middle_query_t> get_query_instance() = 0;
+
+    virtual void set_requirements(output_requirements const &) {}
 };
 
 inline middle_t::~middle_t() = default;

src/options.hpp

@@ -43,6 +43,31 @@ struct database_options_t
     std::string conninfo() const;
 };
 
+/**
+ * Outputs can signal their requirements to the middle by setting these fields.
+ */
+struct output_requirements
+{
+    /**
+     * Need full node objects with tags, attributes (only if --extra-attributes
+     * is set) and locations. If false, only node locations are needed.
+     */
+    bool full_nodes = false;
+
+    /**
+     * Need full way objects with tags, attributes (only if --extra-attributes
+     * is set) and way nodes. If false, only way nodes are needed.
+     */
+    bool full_ways = false;
+
+    /**
+     * Need full relation objects with tags, attributes (only if
+     * --extra-attributes is set) and members. If false, no data from relations
+     * is needed.
+     */
+    bool full_relations = false;
+};
+
 /**
  * Structure for storing command-line and other options
  */

src/osm2pgsql.cpp

@@ -35,6 +35,8 @@ static void run(options_t const &options)
     auto output =
         output_t::create_output(middle->get_query_instance(), options);
 
+    middle->set_requirements(output->get_requirements());
+
     auto dependency_manager = std::unique_ptr<dependency_manager_t>(
         options.with_forward_dependencies
             ? new full_dependency_manager_t{middle}

src/output-flex.cpp

@@ -1402,6 +1402,13 @@ output_flex_t::output_flex_t(
 
     if (!is_clone) {
         init_lua(m_options.style);
+
+        // If the osm2pgsql.select_relation_members() Lua function is defined
+        // it means we need two-stage processing which in turn means we need
+        // the full ways stored in the middle.
+        if (m_select_relation_members) {
+            m_output_requirements.full_ways = true;
+        }
     }
 
     if (m_tables->empty()) {

src/output.hpp

@@ -77,9 +77,15 @@ class output_t
 
     virtual void merge_expire_trees(output_t *other);
 
+    struct output_requirements const &get_requirements() const noexcept
+    {
+        return m_output_requirements;
+    }
+
 protected:
     std::shared_ptr<middle_query_t> m_mid;
     const options_t m_options;
+    output_requirements m_output_requirements{};
 };
 
 #endif // OSM2PGSQL_OUTPUT_HPP

tests/common-import.hpp

@@ -148,6 +148,8 @@ class import_t
         auto output =
             output_t::create_output(middle->get_query_instance(), options);
 
+        middle->set_requirements(output->get_requirements());
+
         auto dependency_manager = std::unique_ptr<dependency_manager_t>(
             options.with_forward_dependencies
                 ? new full_dependency_manager_t{middle}
@@ -183,6 +185,8 @@ class import_t
         auto output =
             output_t::create_output(middle->get_query_instance(), options);
 
+        middle->set_requirements(output->get_requirements());
+
         auto dependency_manager = std::unique_ptr<dependency_manager_t>(
             new full_dependency_manager_t{middle});