Improve error message (#3267)

* Improve error message

* Support pathlib to gmsh

cpp/dolfinx/fem/DirichletBC.cpp

@@ -41,14 +41,16 @@ find_local_entity_index(const mesh::Topology& topology,
   if (!e_to_c)
   {
     throw std::runtime_error(
-        "Entity-to-cell connectivity has not been computed.");
+        "Entity-to-cell connectivity has not been computed. Missing dims "
+        + std::to_string(dim) + "->" + std::to_string(tdim));
   }
 
   auto c_to_e = topology.connectivity(tdim, dim);
   if (!c_to_e)
   {
     throw std::runtime_error(
-        "Cell-to-entity connectivity has not been computed.");
+        "Cell-to-entity connectivity has not been computed. Missing dims "
+        + std::to_string(tdim) + "->" + std::to_string(dim));
   }
 
   std::vector<std::pair<std::int32_t, int>> entity_indices;

python/dolfinx/io/gmshio.py

@@ -6,6 +6,7 @@
 """Tools to extract data from Gmsh models."""
 
 import typing
+from pathlib import Path
 
 from mpi4py import MPI as _MPI
 
@@ -332,7 +333,7 @@ def model_to_mesh(
 
 
 def read_from_msh(
-    filename: str,
+    filename: typing.Union[str, Path],
     comm: _MPI.Comm,
     rank: int = 0,
     gdim: int = 3,
@@ -369,7 +370,7 @@ def read_from_msh(
     if comm.rank == rank:
         gmsh.initialize()
         gmsh.model.add("Mesh from file")
-        gmsh.merge(filename)
+        gmsh.merge(str(filename))
         msh = model_to_mesh(gmsh.model, comm, rank, gdim=gdim, partitioner=partitioner)
         gmsh.finalize()
         return msh