CCE dox and HDF5 error improvements

docs/Tutorials/CCE.md

@@ -205,6 +205,21 @@ values are the complex modes in m-varies-fastest format. That is,
 "Lapse_Re(2,0)", "Lapse_Im(2,0)", "Lapse_Re(2,-1)", "Lapse_Im(2,-1)",
 "Lapse_Re(2,-2)", "Lapse_Im(2,-2)"
 ```
+Each dataset in the file must also have an attribute named "Legend" which
+is an ASCII-encoded null-terminated variable-length string. That is, the HDF5
+type is:
+```
+DATATYPE  H5T_STRING {
+  STRSIZE H5T_VARIABLE;
+  STRPAD H5T_STR_NULLTERM;
+  CSET H5T_CSET_ASCII;
+  CTYPE H5T_C_S1;
+}
+```
+This can be checked for a dataset by running
+```
+h5dump -a DrLapse.dat/Legend CceR0150.h5
+```
 
 The second format is Bondi-Sachs metric component data.
 This format is far more space-efficient (by around a factor of 4), and SpECTRE

src/Evolution/Systems/Cce/BoundaryData.cpp

@@ -15,6 +15,7 @@
 #include "DataStructures/Variables.hpp"
 #include "NumericalAlgorithms/Spectral/SwshCollocation.hpp"
 #include "NumericalAlgorithms/Spectral/SwshDerivatives.hpp"
+#include "Utilities/ErrorHandling/CaptureForError.hpp"
 #include "Utilities/Math.hpp"
 #include "Utilities/SetNumberOfGridPoints.hpp"
 
@@ -484,6 +485,10 @@ void null_vector_l_and_derivatives(
     const tnsr::I<DataVector, 3>& shift,
     const tnsr::I<DataVector, 3>& worldtube_normal) {
   const size_t size = get(lapse).size();
+  CAPTURE_FOR_ERROR(lapse);
+  CAPTURE_FOR_ERROR(dt_lapse);
+  CAPTURE_FOR_ERROR(shift);
+  CAPTURE_FOR_ERROR(dt_shift);
 
   // Allocation
   Variables<tmpl::list<::Tags::TempScalar<0>, ::Tags::TempScalar<1>,
@@ -507,6 +512,7 @@ void null_vector_l_and_derivatives(
     denominator -= spacetime_metric.get(i + 1, i + 1) * shift.get(i) *
                    worldtube_normal.get(i);
   }
+  CAPTURE_FOR_ERROR(denominator);
   // buffer re-use because we won't need the uninverted denominator after this.
   DataVector& one_divided_by_denominator =
       get(get<::Tags::TempScalar<0>>(aggregated_buffer));

src/IO/H5/Helpers.cpp

@@ -10,6 +10,7 @@
 #include <ostream>
 #include <string>
 #include <type_traits>
+#include <typeinfo>
 
 #include "DataStructures/BoostMultiArray.hpp"
 #include "DataStructures/DataVector.hpp"
@@ -473,8 +474,25 @@ std::vector<std::string> read_rank1_attribute<std::string>(
   // Read the strings as arrays of characters
   std::vector<char*> temp(legend_dims[0]);
   const hid_t memtype = h5_type<std::string>();
-  CHECK_H5(H5Aread(attribute_id, memtype, static_cast<void*>(temp.data())),
-           "Failed to read attribute");
+  const hid_t type_in_file = H5Aget_type(attribute_id);
+  CHECK_H5(type_in_file,
+           "Failed to read attribute type from file. Attribute name is '"
+               << name << "'");
+  if (H5Tis_variable_str(type_in_file) < 0) {
+    char* type_name_ptr = H5Tget_tag(type_in_file);
+    const std::string type_name{type_name_ptr};
+    ERROR("The attribute type should be a variable string but got "
+          << type_name);
+    free(type_name_ptr);  // NOLINT
+  }
+  if (H5Tget_cset(type_in_file) != H5T_CSET_ASCII) {
+    ERROR("Expected ASCII-encoded string but got H5T_cset_t of value "
+          << H5Tget_cset(type_in_file)
+          << ". Likely the string is UTF8 encoded.");
+  }
+  CHECK_H5(
+      H5Aread(attribute_id, memtype, static_cast<void*>(temp.data())),
+      "Failed to read attribute: " << name << " with size " << legend_dims);
 
   std::vector<std::string> result(temp.size());
   std::transform(temp.begin(), temp.end(), result.begin(),

src/IO/H5/Type.hpp

@@ -86,6 +86,10 @@ SPECTRE_ALWAYS_INLINE hid_t h5_type<std::string>() {
 #pragma GCC diagnostic ignored "-Wold-style-cast"
   CHECK_H5(H5Tset_size(datatype, H5T_VARIABLE),
            "Failed to set size of string.");
+  CHECK_H5(H5Tset_cset(datatype, H5T_CSET_ASCII),
+           "Failed to set string to ASCII encoding.");
+  CHECK_H5(H5Tset_strpad(datatype, H5T_STR_NULLTERM),
+           "Failed to set string to null terminate");
 #pragma GCC diagnostic pop
   return datatype;
 }