rewritten mesh creator to support more general creation

Automatically create dune grids by different strategies.

1. If a macro file name is given, try to determine by file extension which reader to use and read the grid from file
2. else if the parameter mesh->structured is given, try to construct a structured grid
3. else try to create the grid depending on the grid type

src/amdis/MeshCreator.hpp

@@ -109,8 +109,7 @@ namespace AMDiS
       auto ext = fn.extension();
 
       if (ext == ".msh") {
-        Dune::GmshReader<Grid> reader;
-        return std::unique_ptr<Grid>{reader.read(filename)};
+        return read_gmsh_file<Grid>(filename, Dune::PriorityTag<42>{});
       }
       else if (ext == ".1d" || ext == ".2d" || ext == ".3d" || ext == ".amc") {
         return read_alberta_file<Grid>(filename, Dune::PriorityTag<42>{});
@@ -124,6 +123,29 @@ namespace AMDiS
       }
     }
 
+    template <class GridType>
+    using SupportsGmshReader = decltype(std::declval<Dune::GridFactory<GridType>>().insertBoundarySegment(
+      std::declval<std::vector<unsigned int>>(),
+      std::declval<std::shared_ptr<Dune::BoundarySegment<GridType::dimension, GridType::dimensionworld> >>()) );
+
+    // use GmshReader if GridFactory supports insertBoundarySegments
+    template <class GridType = Grid,
+      REQUIRES(Dune::Std::is_detected<SupportsGmshReader, GridType>::value)>
+    static std::unique_ptr<GridType> read_gmsh_file(std::string const& filename, Dune::PriorityTag<2>)
+    {
+      Dune::GmshReader<GridType> reader;
+      return std::unique_ptr<GridType>{reader.read(filename)};
+    }
+
+    // fallback if GmshReader cannot be used
+    template <class GridType = Grid>
+    static std::unique_ptr<GridType> read_gmsh_file(std::string const& filename, Dune::PriorityTag<0>)
+    {
+      error_exit("Gmsh reader not supported for this grid type!");
+      return {};
+    }
+
+    // read from Alberta file
 
 #if HAVE_ALBERTA
     template <class GridType>
@@ -133,7 +155,7 @@ namespace AMDiS
     template <class GridType = Grid,
       REQUIRES(GridType::dimensionworld == WORLDDIM),
       REQUIRES(Dune::Std::is_detected<IsAlbertaGrid, GridType>::value)>
-    static std::unique_ptr<Grid> read_alberta_file(std::string const& filename, Dune::PriorityTag<3>)
+    static std::unique_ptr<GridType> read_alberta_file(std::string const& filename, Dune::PriorityTag<3>)
     {
       return std::make_unique<GridType>(filename);
     }
@@ -141,7 +163,7 @@ namespace AMDiS
     // use a gridfactory and the generic AlbertaReader
     template <class GridType = Grid,
       REQUIRES(GridType::dimensionworld == WORLDDIM)>
-    static std::unique_ptr<Grid> read_alberta_file(std::string const& filename, Dune::PriorityTag<2>)
+    static std::unique_ptr<GridType> read_alberta_file(std::string const& filename, Dune::PriorityTag<2>)
     {
       Dune::GridFactory<GridType> factory;
       Dune::AlbertaReader<GridType> reader;