Improve type reporting in UnknownArrayHandle

Added features with reporting types with `UnknownArrayHandle`. First,
added a method named `GetArrayTypeName` that returns a string containing
the type of the contained array. There were already methods
`GetValueType` and `GetStorageType`, but this provides a convenience to
get the whole name in one go.

Also improved the reporting when an `AsArrayHandle` call failed. Before,
the thrown method just reported that the `UnknownArrayHandle` could not
be converted to the given type. Now, it also reports the type actually
held by the `UnknownArrayHandle` so the user can better understand why
the conversion failed.

docs/changelog/better-unknown-type-reporting.md

@@ -0,0 +1,14 @@
+# Improve type reporting in `UnknownArrayHandle`
+
+Added features with reporting types with `UnknownArrayHandle`. First, added
+a method named `GetArrayTypeName` that returns a string containing the type
+of the contained array. There were already methods `GetValueType` and
+`GetStorageType`, but this provides a convenience to get the whole name in
+one go.
+
+Also improved the reporting when an `AsArrayHandle` call failed. Before,
+the thrown method just reported that the `UnknownArrayHandle` could not be
+converted to the given type. Now, it also reports the type actually held by
+the `UnknownArrayHandle` so the user can better understand why the
+conversion failed.
+

vtkm/cont/ArrayRangeCompute.cxx

@@ -237,7 +237,7 @@ vtkm::cont::ArrayHandle<vtkm::Range> ArrayRangeCompute(const vtkm::cont::Unknown
       return ArrayRangeCompute(array.AsArrayHandle<vtkm::cont::ArrayHandleIndex>(), device);
     }
   }
-  catch (vtkm::cont::ErrorBadValue&)
+  catch (vtkm::cont::ErrorBadType&)
   {
     // If a cast/call failed, try falling back to a more general implementation.
   }

vtkm/cont/UnknownArrayHandle.cxx

@@ -201,6 +201,19 @@ VTKM_CONT std::string UnknownArrayHandle::GetStorageTypeName() const
   }
 }
 
+VTKM_CONT std::string UnknownArrayHandle::GetArrayTypeName() const
+{
+  if (this->Container)
+  {
+    return "vtkm::cont::ArrayHandle<" + this->GetValueTypeName() + ", " +
+      this->GetStorageTypeName() + ">";
+  }
+  else
+  {
+    return "";
+  }
+}
+
 VTKM_CONT vtkm::Id UnknownArrayHandle::GetNumberOfValues() const
 {
   if (this->Container)
@@ -297,7 +310,7 @@ VTKM_CONT_EXPORT void ThrowCastAndCallException(const vtkm::cont::UnknownArrayHa
          "Array: ";
   ref.PrintSummary(out);
   out << "TypeList: " << vtkm::cont::TypeToString(type) << "\n";
-  throw vtkm::cont::ErrorBadValue(out.str());
+  throw vtkm::cont::ErrorBadType(out.str());
 }
 
 } // namespace detail

vtkm/cont/UnknownArrayHandle.h

@@ -447,6 +447,13 @@ public:
   /// Returns an empty string if no array is stored.
   VTKM_CONT std::string GetStorageTypeName() const;
 
+  /// \brief Returns a string representation of the underlying data type.
+  ///
+  /// The returned string will be of the form `vtkm::cont::ArrayHandle<T, S>` rather than the name
+  /// of an actual subclass. If no array is stored, an empty string is returned.
+  ///
+  VTKM_CONT std::string GetArrayTypeName() const;
+
   /// Returns true if this array matches the ValueType template argument.
   ///
   template <typename ValueType>
@@ -580,7 +587,7 @@ public:
     if (!this->IsType<ArrayType>())
     {
       VTKM_LOG_CAST_FAIL(*this, decltype(array));
-      throwFailedDynamicCast(vtkm::cont::TypeToString(*this), vtkm::cont::TypeToString(array));
+      throwFailedDynamicCast(this->GetArrayTypeName(), vtkm::cont::TypeToString(array));
     }
 
     array = *reinterpret_cast<ArrayType*>(this->Container->ArrayHandlePointer);

vtkm/cont/testing/UnitTestUnknownArrayHandle.cxx

@@ -90,8 +90,8 @@ struct CheckFunctor
   void operator()(const vtkm::cont::ArrayHandle<T, S>& array, bool& called) const
   {
     called = true;
-    std::cout << "  Checking for array type " << typeid(T).name() << " with storage "
-              << typeid(S).name() << std::endl;
+    std::cout << "  Checking for array type " << vtkm::cont::TypeToString<T>() << " with storage "
+              << vtkm::cont::TypeToString<S>() << std::endl;
 
     CheckArray(array);
   }
@@ -100,6 +100,8 @@ struct CheckFunctor
 void BasicUnknownArrayChecks(const vtkm::cont::UnknownArrayHandle& array,
                              vtkm::IdComponent numComponents)
 {
+  std::cout << "  Checking an UnknownArrayHandle containing " << array.GetArrayTypeName()
+            << std::endl;
   VTKM_TEST_ASSERT(array.GetNumberOfValues() == ARRAY_SIZE,
                    "Dynamic array reports unexpected size.");
   VTKM_TEST_ASSERT(array.GetNumberOfComponentsFlat() == numComponents,
@@ -388,6 +390,10 @@ struct TryBasicVTKmType
   {
     vtkm::cont::UnknownArrayHandle array = CreateArrayUnknown(T());
 
+    VTKM_TEST_ASSERT(array.GetValueTypeName() == vtkm::cont::TypeToString<T>());
+    VTKM_TEST_ASSERT(array.GetStorageTypeName() ==
+                     vtkm::cont::TypeToString<vtkm::cont::StorageTagBasic>());
+
     CheckUnknownArray<vtkm::TypeListAll, VTKM_DEFAULT_STORAGE_LIST>(
       array, vtkm::VecTraits<T>::NUM_COMPONENTS);
 
@@ -405,7 +411,7 @@ void TryUnusualType()
     CheckUnknownArray<VTKM_DEFAULT_TYPE_LIST, VTKM_DEFAULT_STORAGE_LIST>(array, 1);
     VTKM_TEST_FAIL("CastAndCall failed to error for unrecognized type.");
   }
-  catch (vtkm::cont::ErrorBadValue&)
+  catch (vtkm::cont::ErrorBadType&)
   {
     std::cout << "  Caught exception for unrecognized type." << std::endl;
   }

vtkm/cont/testing/UnitTestVariantArrayHandle.cxx

@@ -457,7 +457,7 @@ void TryUnusualType()
     CheckArrayVariant(array, 1, true);
     VTKM_TEST_FAIL("CastAndCall failed to error for unrecognized type.");
   }
-  catch (vtkm::cont::ErrorBadValue&)
+  catch (vtkm::cont::ErrorBadType&)
   {
     std::cout << "  Caught exception for unrecognized type." << std::endl;
   }