Allow detecting duplicate nodes in ways when creating geometry

When linestrings or polygons are created from ways, duplicate nodes are
removed automatically. Generally this is what you want. But sometimes
it makes sense to be able to detect this situation, for instance when
creating some debug output.

The information is available on the C++ side anyway, this change exposes
this information in the Lua code as a second return parameter of the
as_linestring and as_polygon functions which can be ignored during
normal use.

Author: joto

src/geom-from-osm.cpp

@@ -85,13 +85,15 @@ void fill_polygon(polygon_t *polygon, osmium::Area const &area,
 
 } // anonymous namespace
 
-void create_linestring(geometry_t *geom, osmium::Way const &way)
+bool create_linestring(geometry_t *geom, osmium::Way const &way)
 {
     auto &line = geom->set<linestring_t>();
 
     if (!fill_point_list(&line, way.nodes())) {
         geom->reset();
     }
+
+    return way.nodes().size() == line.size();
 }
 
 geometry_t create_linestring(osmium::Way const &way)
@@ -101,28 +103,30 @@ geometry_t create_linestring(osmium::Way const &way)
     return geom;
 }
 
-void create_polygon(geometry_t *geom, osmium::Way const &way,
+bool create_polygon(geometry_t *geom, osmium::Way const &way,
                     osmium::memory::Buffer *area_buffer)
 {
     auto &polygon = geom->set<polygon_t>();
 
     // A closed way with less than 4 nodes can never be a valid polygon
     if (way.nodes().size() < 4U) {
         geom->reset();
-        return;
+        return false;
     }
 
     geom::area_assembler_t assembler{area_buffer};
 
     if (!assembler(way)) {
         geom->reset();
-        return;
+        return false;
     }
 
     auto const &area = assembler.get_area();
     auto const &ring = *area.cbegin<osmium::OuterRing>();
 
     fill_point_list(&polygon.outer(), ring);
+
+    return assembler.stats().duplicate_nodes == 0;
 }
 
 geometry_t create_polygon(osmium::Way const &way,

src/geom-from-osm.hpp

@@ -63,7 +63,7 @@ void create_point(geometry_t *geom, osmium::Node const &node);
  * \param geom Pointer to an existing geometry which will be used as output.
  * \param way The input way.
  */
-void create_linestring(geometry_t *geom, osmium::Way const &way);
+bool create_linestring(geometry_t *geom, osmium::Way const &way);
 
 /**
  * Create a linestring geometry from a way. Nodes without location are ignored.
@@ -87,7 +87,7 @@ void create_linestring(geometry_t *geom, osmium::Way const &way);
  * \param way The input way.
  * \param area_buffer Temporary buffer used to create area.
  */
-void create_polygon(geometry_t *geom, osmium::Way const &way,
+bool create_polygon(geometry_t *geom, osmium::Way const &way,
                     osmium::memory::Buffer *area_buffer);
 
 /**

src/output-flex.cpp

@@ -504,9 +504,14 @@ int output_flex_t::app_as_linestring()
     m_way_cache.add_nodes(middle());
 
     auto *geom = create_lua_geometry_object(lua_state());
-    geom::create_linestring(geom, m_way_cache.get());
+    bool const okay = geom::create_linestring(geom, m_way_cache.get());
 
-    return 1;
+    if (geom->is_null()) {
+        return 1;
+    }
+
+    lua_pushboolean(lua_state(), okay);
+    return 2;
 }
 
 int output_flex_t::app_as_polygon()
@@ -517,9 +522,15 @@ int output_flex_t::app_as_polygon()
     m_way_cache.add_nodes(middle());
 
     auto *geom = create_lua_geometry_object(lua_state());
-    geom::create_polygon(geom, m_way_cache.get(), &m_area_buffer);
+    bool const okay =
+        geom::create_polygon(geom, m_way_cache.get(), &m_area_buffer);
 
-    return 1;
+    if (geom->is_null()) {
+        return 1;
+    }
+
+    lua_pushboolean(lua_state(), okay);
+    return 2;
 }
 
 int output_flex_t::app_as_multipoint()

tests/bdd/flex/geometry-linestring.feature

@@ -66,3 +66,46 @@ Feature: Creating linestring features from way
             Geometry data for geometry column 'geom' has the wrong type (LINESTRING).
             """
 
+    Scenario:
+        Given the grid
+            | 1 | 2 |   |
+            |   |   | 3 |
+        And the OSM data
+            """
+            w20 Thighway=motorway Nn1,n2,n3,n1
+            w21 Thighway=motorway Nn1,n2,n2,n3,n1
+            w22 Thighway=motorway Nn1,n2,n3,n1,n1
+            w23 Thighway=motorway Nn1,n2,n3
+            w24 Thighway=motorway Nn2,n2
+            """
+        And the lua style
+            """
+            local lines = osm2pgsql.define_way_table('osm2pgsql_test_lines', {
+                { column = 'lgeom', type = 'linestring', projection = 4326 },
+                { column = 'pgeom', type = 'polygon', projection = 4326 },
+                { column = 'lclean', type = 'bool' },
+                { column = 'pclean', type = 'bool' },
+            })
+
+            function osm2pgsql.process_way(object)
+                lgeom, lclean = object:as_linestring()
+                pgeom, pclean = object:as_polygon()
+                lines:insert({
+                    lgeom = lgeom,
+                    pgeom = pgeom,
+                    lclean = lclean,
+                    pclean = pclean,
+                })
+            end
+
+            """
+        When running osm2pgsql flex
+
+        Then table osm2pgsql_test_lines contains exactly
+            | way_id | lgeom!geo  | lclean | pgeom!geo    | pclean |
+            | 20     | 1, 2, 3, 1 | True   | (1, 2, 3, 1) | True   |
+            | 21     | 1, 2, 3, 1 | False  | (1, 2, 3, 1) | False  |
+            | 22     | 1, 2, 3, 1 | False  | (1, 2, 3, 1) | False  |
+            | 23     | 1, 2, 3    | True   | NULL         | NULL   |
+            | 24     | NULL       | NULL   | NULL         | NULL   |
+