Commit c3889a1a authored by Kenneth Moreland's avatar Kenneth Moreland

Give better error reporting when an Invoke parameter is wrong

When one of the parameters to DispatcherBase::Invoke is incorrect, you
get an error in a strange place. It is deep in a call stack using some
heavily templated types rather than where the Invoke is actually called.

Formerly, the code was structured to give a very obfuscated error
message. Try to make this easier on users by first adding helpful hints
in the code around where the error is to explain why the error occured
and helpful advice on how to track down the problem. Second, reconfigure
the static_assert so that the compiler gives a readable error message.
Third, add some auxiliary error messages that provide additional
information about the types and classes involved in the error.
parent 6b5cbe31
......@@ -76,12 +76,18 @@ inline void PrintFailureMessage(int index)
throw vtkm::cont::ErrorBadType(message.str());
template <bool, typename T, typename TypeCheckTag>
struct ParameterTypeCorrect;
template <typename T, typename TypeCheckTag>
struct ParameterTypeCorrect<true, T, TypeCheckTag>
template <typename T, bool noError>
struct ReportTypeOnError;
template <typename T>
struct ReportTypeOnError<T, true> : std::true_type
template <int Value, bool noError>
struct ReportValueOnError;
template <int Value>
struct ReportValueOnError<Value, true> : std::true_type
static VTKM_CONSTEXPR bool value = true;
// Is designed as a brigand fold operation.
......@@ -97,20 +103,51 @@ struct DetermineIfHasDynamicParameter
// Is designed as a brigand fold operation.
template <typename T, typename State, typename SigTypes>
struct DetermineHasInCorrectParameters
template <typename WorkletType>
struct DetermineHasCorrectParameters
//T is the type of the Param at the current index
//State if the index to use to fetch the control signature tag
using ControlSignatureTag = typename brigand::at_c<SigTypes, State::value>;
using TypeCheckTag = typename ControlSignatureTag::TypeCheckTag;
using isCorrect =
ParameterTypeCorrect<vtkm::cont::arg::TypeCheck<TypeCheckTag, T>::value, TypeCheckTag, T>;
"The type check failed since the parameter passed in doesn't pass the TypeCheck");
using type = std::integral_constant<std::size_t, State::value + 1>;
template <typename T, typename State, typename SigTypes>
struct Functor
//T is the type of the Param at the current index
//State if the index to use to fetch the control signature tag
using ControlSignatureTag = typename brigand::at_c<SigTypes, State::value>;
using TypeCheckTag = typename ControlSignatureTag::TypeCheckTag;
static VTKM_CONSTEXPR bool isCorrect = vtkm::cont::arg::TypeCheck<TypeCheckTag, T>::value;
// If you get an error on the line below, that means that your code has called the
// Invoke method on a dispatcher, and one of the arguments of the Invoke is the wrong
// type. Each argument of Invoke corresponds to a tag in the arguments of the
// ControlSignature of the worklet. If there is a mismatch, then you get an error here
// (instead of where you called the dispatcher). For example, if the worklet has a
// control signature as ControlSignature(CellSetIn, ...) and the first argument passed
// to Invoke is an ArrayHandle, you will get an error here because you cannot use an
// ArrayHandle in place of a CellSetIn argument. (You need to use a CellSet.) See a few
// lines later for some diagnostics to help you trace where the error occured.
// If you are getting the error described above, the following lines will give you some
// diagnostics (in the form of compile errors). Each one will result in a compile error
// reporting an undefined type for ReportTypeOnError (or ReportValueOnError). What we are
// really reporting is the first template argument, which is one of the types or values that
// should help pinpoint where the error is. The comment for static_assert provides the
// type/value being reported. (Note that some compilers report better types than others. If
// your compiler is giving unhelpful types like "T" or "WorkletType", you may need to try a
// different compiler.)
static_assert(ReportTypeOnError<T, isCorrect>::value, "Type passed to Invoke");
static_assert(ReportTypeOnError<WorkletType, isCorrect>::value, "Worklet being invoked.");
static_assert(ReportValueOnError<State::value, isCorrect>::value, "Index of Invoke parameter");
static_assert(ReportTypeOnError<TypeCheckTag, isCorrect>::value, "Type check tag used");
// This final static_assert gives a human-readable error message. Ideally, this would be
// placed first, but some compilers will suppress further errors when a static_assert
// fails, so you would not see the other diagnostic error messages.
"The type of one of the arguments to the dispatcher's Invoke method is "
"incompatible with the corresponding tag in the worklet's ControlSignature.");
using type = std::integral_constant<std::size_t, State::value + 1>;
// Checks that an argument in a ControlSignature is a valid control signature
......@@ -389,12 +426,11 @@ private:
typename WorkletType::ControlSignature>::Parameters;
//isAllValid will throw a compile error if everything doesn't match
using isAllValid =
std::integral_constant<std::size_t, 0>,
using isAllValid = brigand::fold<
std::integral_constant<std::size_t, 0>,
typename detail::DetermineHasCorrectParameters<WorkletType>::
template Functor<brigand::_element, brigand::_state, brigand::pin<ContSigTypes>>>;
//this warning exists so that we don't get a warning from not using isAllValid
using expectedLen = std::integral_constant<std::size_t, sizeof...(Args)>;
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