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Constrain tuple_of_iterator_references -> tuple conversion on element convertibility (fixes GCC 9 build break) #9284

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Constrain tuple_of_iterator_references -> tuple conversion on element convertibility (fixes GCC 9 build break) #9284

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22 changes: 21 additions & 1 deletion libcudacxx/include/cuda/std/__tuple_dir/tuple.h
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,22 @@

_CCCL_BEGIN_NAMESPACE_CUDA_STD

// Determines whether each element of a tuple_of_iterator_references can actually construct the
// corresponding tuple element. The tuple_of_iterator_references converting constructor below is
// otherwise unconstrained on element convertibility, so is_constructible would report true even for
// ill-formed conversions (e.g. tuple_of_iterator_references<const int&> -> tuple<int&>) and then
// hard-error when the delegating constructor body is instantiated -- which happens during a
// contiguous_iterator concept check on a thrust zip_iterator under GCC 9.
template <class _TupleTypes, class _TupleOfIteratorReferences, class _Indices>
inline constexpr bool __tuple_of_iterator_references_constructible_v = false;

template <class... _Tp, class _TupleOfIteratorReferences, size_t... _Indices>
inline constexpr bool __tuple_of_iterator_references_constructible_v<__tuple_types<_Tp...>,
_TupleOfIteratorReferences,
__tuple_indices<_Indices...>> =
(is_constructible_v<_Tp, decltype(::cuda::std::get<_Indices>(::cuda::std::declval<_TupleOfIteratorReferences>()))>
&& ...);
Comment on lines +56 to +64

@coderabbitai coderabbitai Bot Jun 6, 2026

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⚠️ Potential issue | 🟡 Minor

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail
file="libcudacxx/include/cuda/std/__tuple_dir/tuple.h"
# Show the include block and the trait segment around the reported lines
sed -n '1,120p' "$file"

Repository: NVIDIA/cccl

Length of output: 5434

🏁 Script executed:

#!/bin/bash
set -euo pipefail

# Check whether forward.h (or other directly-included headers) provides declval
rg -n "declval" libcudacxx/include/cuda/std/__utility/forward.h libcudacxx/include/cuda/std/__utility/move.h libcudacxx/include/cuda/std/__utility/pair.h libcudacxx/include/cuda/std/__utility/swap.h || true

# Show the actual declval declaration/definition location
rg -n "template\s*<.*>\s*.*declval|struct\s*declval|declval\(" libcudacxx/include/cuda/std/__utility/declval.h || true

Repository: NVIDIA/cccl

Length of output: 219

🏁 Script executed:

#!/bin/bash
set -euo pipefail
file="libcudacxx/include/cuda/std/__utility/forward.h"
sed -n '1,140p' "$file"

Repository: NVIDIA/cccl

Length of output: 3404

🏁 Script executed:

#!/bin/bash
set -euo pipefail
file="libcudacxx/include/cuda/std/__tuple_dir/tuple.h"

rg -n "declval\.h" "$file" || true
rg -n "__utility/declval\.h" "$file" || true
rg -n "declval<" "$file" || true

Repository: NVIDIA/cccl

Length of output: 175

🏁 Script executed:

#!/bin/bash
set -euo pipefail

# Where is declval.h included from?
rg -n --max-count 50 "cuda/std/__utility/declval\.h" libcudacxx/include/cuda/std || true

# Where is the underlying __declval declared/defined?
rg -n --max-count 50 "__declval" libcudacxx/include/cuda/std/__utility libcudacxx/include/cuda/std || true

Repository: NVIDIA/cccl

Length of output: 6378

suggestion: Add a direct include for declval in libcudacxx/include/cuda/std/__tuple_dir/tuple.h since __tuple_of_iterator_references_constructible_v uses ::cuda::std::declval; the current build relies on a transitive include via tuple_constraints.h.

diff 
 `#include` <cuda/std/__utility/forward.h>
+#include <cuda/std/__utility/declval.h>
 `#include` <cuda/std/__utility/move.h>

Source: Coding guidelines


template <class... _Tp>
class _CCCL_TYPE_VISIBILITY_DEFAULT tuple
{
Expand Down Expand Up @@ -225,7 +241,11 @@ class _CCCL_TYPE_VISIBILITY_DEFAULT tuple
// NOLINTBEGIN(modernize-type-traits)
enable_if_t<__is_tuple_of_iterator_references_v<_TupleOfIteratorReferences>, int> = 0,
// NOLINTEND(modernize-type-traits)
enable_if_t<(tuple_size<_TupleOfIteratorReferences>::value == sizeof...(_Tp)), int> = 0>
enable_if_t<(tuple_size<_TupleOfIteratorReferences>::value == sizeof...(_Tp)), int> = 0,
enable_if_t<__tuple_of_iterator_references_constructible_v<__tuple_types<_Tp...>,
_TupleOfIteratorReferences,
__make_tuple_indices_t<sizeof...(_Tp)>>,
int> = 0>
_CCCL_API constexpr tuple(_TupleOfIteratorReferences&& __t)
: tuple(::cuda::std::forward<_TupleOfIteratorReferences>(__t), __make_tuple_indices_t<sizeof...(_Tp)>{})
{}
Expand Down
7 changes: 6 additions & 1 deletion thrust/thrust/iterator/detail/tuple_of_iterator_references.h
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Original file line number Diff line number Diff line change
Expand Up @@ -168,7 +168,12 @@ class tuple_of_iterator_references : public ::cuda::std::tuple<Ts...>

template <
class... Us,
::cuda::std::enable_if_t<is_compatible_tuple_v<::cuda::std::tuple<Us...>, ::cuda::std::tuple<Ts...>>, int> = 0>
::cuda::std::enable_if_t<is_compatible_tuple_v<::cuda::std::tuple<Us...>, ::cuda::std::tuple<Ts...>>, int> = 0,
// Structure compatibility alone is not enough: each held reference must actually convert to the
// requested element, otherwise this operator is selected for ill-formed conversions such as
// tuple_of_iterator_references<const int&> -> tuple<int&>, which then hard-errors in the body
// (e.g. during a contiguous_iterator concept check on a zip_iterator under GCC 9).
::cuda::std::enable_if_t<(::cuda::std::is_convertible_v<Ts, Us> && ...), int> = 0>
_CCCL_HOST_DEVICE constexpr operator ::cuda::std::tuple<Us...>() const
Comment on lines 169 to 177

@coderabbitai coderabbitai Bot Jun 6, 2026

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⚠️ Potential issue | 🟡 Minor

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail

FILE="thrust/thrust/iterator/detail/tuple_of_iterator_references.h"

echo "== Includes in $FILE =="
sed -n '1,120p' "$FILE" | nl -ba | sed -n '1,120p'

echo
echo "== Search for is_convertible_v =="
rg -n "::cuda::std::is_convertible_v" "$FILE"

echo
echo "== Show surrounding code for the operator constraints =="
sed -n '140,220p' "$FILE" | nl -ba

Repository: NVIDIA/cccl

Length of output: 195

🏁 Script executed:

#!/bin/bash
set -euo pipefail

FILE="thrust/thrust/iterator/detail/tuple_of_iterator_references.h"

echo "== Top of file (includes) =="
sed -n '1,80p' "$FILE" | cat -n

echo
echo "== Search for is_convertible_v =="
rg -n "::cuda::std::is_convertible_v" "$FILE" || true

echo
echo "== Surrounding code (lines ~140-220) =="
sed -n '140,220p' "$FILE" | cat -n

Repository: NVIDIA/cccl

Length of output: 6797

🏁 Script executed:

#!/bin/bash
set -euo pipefail

# 1) Confirm where is_convertible_v is defined
rg -n "is_convertible_v" libcudacxx cuda 2>/dev/null | head -n 50

# 2) Find the specific header that defines it (search by filename + symbol)
fd "is_convertible" -a . 2>/dev/null | head -n 50

# 3) Inspect that header's contents around the definition
H=$(fd "is_convertible.h" -a . 2>/dev/null | head -n 1 || true)
echo "First match for is_convertible.h: $H"
if [ -n "${H:-}" ]; then
  sed -n '1,120p' "$H" | cat -n
  rg -n "is_convertible_v" "$H" || true
fi

# 4) Check whether already-included headers include is_convertible.h
INCLUDES=(
  "cuda/std/__type_traits/common_reference.h"
  "cuda/std/__type_traits/enable_if.h"
)
for inc in "${INCLUDES[@]}"; do
  f=$(fd "$(basename "$inc")" cuda libcudacxx 2>/dev/null | head -n 1 || true)
  echo "Resolved $inc -> $f"
  if [ -n "${f:-}" ]; then
    rg -n "`#include` <cuda/std/__type_traits/is_convertible.h>" "$f" || true
    rg -n "is_convertible" "$f" | head -n 20 || true
  fi
done

Repository: NVIDIA/cccl

Length of output: 7578

🏁 Script executed:

#!/bin/bash
set -euo pipefail

# Inspect common_reference.h and enable_if.h for is_convertible includes
for f in \
  "libcudacxx/include/cuda/std/__type_traits/common_reference.h" \
  "libcudacxx/include/cuda/std/__type_traits/enable_if.h" \
  "libcudacxx/include/cuda/std/__tuple_dir/tuple_constraints.h" \
  "libcudacxx/include/cuda/std/__tuple_dir/tuple_element.h" \
  "libcudacxx/include/cuda/std/tuple"; do
  if [ -f "$f" ]; then
    echo "==== $f (top includes) ===="
    sed -n '1,120p' "$f" | cat -n
    echo
    rg -n "`#include` <cuda/std/__type_traits/is_convertible.h>" "$f" || true
    echo
  fi
done

Repository: NVIDIA/cccl

Length of output: 18739

suggestion: tuple_of_iterator_references.h uses ::cuda::std::is_convertible_v in the tuple-conversion SFINAE; add an explicit #include <cuda/std/__type_traits/is_convertible.h> instead of relying on transitive inclusion (currently comes via cuda/std/__type_traits/common_reference.h).

Proposed diff 
 `#include` <cuda/std/__type_traits/common_reference.h>
 `#include` <cuda/std/__type_traits/enable_if.h>
+#include <cuda/std/__type_traits/is_convertible.h>
 `#include` <cuda/std/__utility/move.h>

Source: Coding guidelines

{
return __to_tuple<Us...>(typename ::cuda::std::__make_tuple_indices<sizeof...(Ts)>::type{});
Expand Down
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