Check GEOS version is <= 3.5.

The current code only works with GEOS up to 3.5, because there were
changes in the C++ API of GEOS that we are using. Using the C++ API was
probably a bad idea anyway, because the GEOS project doesn't consider
the C++ API to be a stable external API. It would be better to use the
stable C API of GEOS, but until somebody needs that and is willing
to implement it, we will not have that.

include/osmium/geom/geos.hpp

@@ -33,12 +33,22 @@ DEALINGS IN THE SOFTWARE.
 
 */
 
+#include <geos/version.h>
+#if defined(GEOS_VERSION_MAJOR) && defined(GEOS_VERSION_MINOR) && (GEOS_VERSION_MAJOR < 3 || (GEOS_VERSION_MAJOR == 3 && GEOS_VERSION_MINOR <= 5))
+
+#define OSMIUM_WITH_GEOS
+
 /**
  * @file
  *
- * This file contains code for conversion of OSM geometries into GDAL
+ * This file contains code for conversion of OSM geometries into GEOS
  * geometries.
  *
+ * Note that everything in this file is deprecated and only works up to
+ * GEOS 3.5. It uses the GEOS C++ API which the GEOS project does not consider
+ * to be a stable, external API. We probably should have used the GEOS C API
+ * instead.
+ *
  * @attention If you include this file, you'll need to link with `libgeos`.
  */
 
@@ -88,6 +98,7 @@ namespace osmium {
 
         namespace detail {
 
+            /// @deprecated
             class GEOSFactoryImpl {
 
                 std::unique_ptr<const geos::geom::PrecisionModel> m_precision_model;
@@ -245,6 +256,7 @@ namespace osmium {
 
         } // namespace detail
 
+        /// @deprecated
         template <typename TProjection = IdentityProjection>
         using GEOSFactory = GeometryFactory<osmium::geom::detail::GEOSFactoryImpl, TProjection>;
 
@@ -254,4 +266,6 @@ namespace osmium {
 
 #undef THROW
 
+#endif
+
 #endif // OSMIUM_GEOM_GEOS_HPP

test/t/geom/test_geos.cpp

@@ -1,6 +1,10 @@
-#include "catch.hpp"
 
 #include <osmium/geom/geos.hpp>
+
+#ifdef OSMIUM_WITH_GEOS
+
+#include "catch.hpp"
+
 #include <osmium/geom/mercator_projection.hpp>
 
 #include "area_helper.hpp"
@@ -144,3 +148,5 @@ TEST_CASE("GEOS geometry factory - create area with two outer and two inner ring
     REQUIRE(5 == l1e->getNumPoints());
 }
 
+#endif
+