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Ensure that we properly warn about device lambdas that need to query the return type #6765

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Merged
bernhardmgruber merged 2 commits into from
Nov 25, 2025
Merged

Ensure that we properly warn about device lambdas that need to query the return type #6765

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5d363b5
Ensure that we properly check if a device lambda is wrapped
miscco Nov 24, 2025
65e0606
Ensure that `thrust::transform_iterator` properly checks for device l…
miscco Nov 24, 2025
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8 changes: 5 additions & 3 deletions libcudacxx/include/cuda/std/__functional/invoke.h
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@
#include <cuda/std/__type_traits/is_same.h>
#include <cuda/std/__type_traits/is_void.h>
#include <cuda/std/__type_traits/nat.h>
#include <cuda/std/__type_traits/remove_cvref.h>
#include <cuda/std/__utility/declval.h>
#include <cuda/std/__utility/forward.h>

Expand Down Expand Up @@ -192,15 +193,16 @@ struct _CCCL_TYPE_VISIBILITY_DEFAULT invoke_result //
{
#if _CCCL_CUDA_COMPILER(NVCC) && defined(__CUDACC_EXTENDED_LAMBDA__) && !_CCCL_DEVICE_COMPILATION()
# if _CCCL_CUDACC_BELOW(12, 3)
static_assert(!__nv_is_extended_device_lambda_closure_type(_Fp),
static_assert(!__nv_is_extended_device_lambda_closure_type(remove_cvref_t<_Fp>),
"Attempt to use an extended __device__ lambda in a context "
"that requires querying its return type in host code. Use a "
"named function object, an extended __host__ __device__ lambda, or "
"cuda::proclaim_return_type instead.");
# else // ^^^ _CCCL_CUDACC_BELOW(12, 3) ^^^ / vvv _CCCL_CUDACC_AT_LEAST(12, 3) vvv
static_assert(
!__nv_is_extended_device_lambda_closure_type(_Fp) || __nv_is_extended_host_device_lambda_closure_type(_Fp)
|| __nv_is_extended_device_lambda_with_preserved_return_type(_Fp),
!__nv_is_extended_device_lambda_closure_type(remove_cvref_t<_Fp>)
|| __nv_is_extended_host_device_lambda_closure_type(remove_cvref_t<_Fp>)
|| __nv_is_extended_device_lambda_with_preserved_return_type(remove_cvref_t<_Fp>),
"Attempt to use an extended __device__ lambda in a context "
"that requires querying its return type in host code. Use a "
"named function object, an extended __host__ __device__ lambda, "
Expand Down
8 changes: 4 additions & 4 deletions thrust/thrust/iterator/transform_iterator.h
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Original file line number Diff line number Diff line change
Expand Up @@ -48,12 +48,12 @@
#include <thrust/iterator/iterator_traits.h>

#include <cuda/std/__functional/identity.h>
#include <cuda/std/__functional/invoke.h>
#include <cuda/std/__memory/construct_at.h>
#include <cuda/std/__type_traits/is_copy_assignable.h>
#include <cuda/std/__type_traits/is_copy_constructible.h>
#include <cuda/std/__type_traits/remove_cvref.h>
#include <cuda/std/__type_traits/remove_reference.h>
#include <cuda/std/__utility/declval.h>

THRUST_NAMESPACE_BEGIN

Expand All @@ -66,7 +66,7 @@ template <class UnaryFunc, class Iterator>
struct transform_iterator_reference
{
// by default, dereferencing the iterator yields the same as the function.
using type = decltype(::cuda::std::declval<UnaryFunc>()(::cuda::std::declval<it_value_t<Iterator>>()));
using type = ::cuda::std::invoke_result_t<UnaryFunc&, it_value_t<Iterator>>;
};

// for certain function objects, we need to tweak the reference type. Notably, identity functions must decay to values.
Expand All @@ -79,8 +79,8 @@ struct transform_iterator_reference<::cuda::std::identity, Iterator>
template <typename Eval, class Iterator>
struct transform_iterator_reference<functional::actor<Eval>, Iterator>
{
using type = ::cuda::std::remove_reference_t<decltype(::cuda::std::declval<functional::actor<Eval>>()(
::cuda::std::declval<it_value_t<Iterator>>()))>;
using type =
::cuda::std::remove_reference_t<::cuda::std::invoke_result_t<functional::actor<Eval>&, it_value_t<Iterator>>>;
};

// Type function to compute the iterator_adaptor instantiation to be used for transform_iterator
Expand Down
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