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Fix nvcc CUDA 12.0/12.1 C++20 ranges parse error (#3907)

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The diagnostic matrix in this PR confirmed the affected range exactly:
nvcc 12.0.1 and 12.1.1 both fail with "expected initializer before
'<' token" on iteration_proxy.hpp's enable_borrowed_range variable
template specialization at -std=c++20; 12.2.2 and newer already build
cleanly. Guard JSON_HAS_RANGES off for that narrow nvcc version range,
matching the existing GCC-11/libstdc++ carve-outs in the same ifdef
chain, and regenerate single_include accordingly.

Broaden the CUDA smoke test to also exercise comparisons
(operator==/operator<=>, gated independently by
JSON_HAS_THREE_WAY_COMPARISON) and range-based iteration, not just
dump()/erase(), so the fix's actual scope is evidenced by CI rather
than assumed from the single reported symptom.

Have tests/cuda_example/CMakeLists.txt pick the newest C++ standard
the detected nvcc version actually supports (20/17/11) instead of
hard-requiring C++20, so older toolkits build at a lower standard
instead of failing CMake configure outright. This is test-project-local
only; the JSON_HAS_RANGES guard is what protects real client code,
since a header can't control what -std= flag it's compiled with.

Right-size the CI matrix from the 8-version diagnostic sweep down to
11.8.0 (C++17 fallback path) / 12.1.1 (permanent #3907 regression
guard) / 12.6.3 (recent coverage), and update the compiler-version
table in the quality assurance docs to match.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-07-09 07:12:01 +02:00
parent f3d48e4f2f
commit 8917c42bbc
6 changed files with 45 additions and 6 deletions
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include/nlohmann/detail/macro_scope.hpp
+5
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@@ -146,6 +146,11 @@
#define JSON_HAS_RANGES 0
#elif defined(_LIBCPP_VERSION) && _LIBCPP_VERSION < 160000
#define JSON_HAS_RANGES 0
// nvcc CUDA 12.0/12.1 chokes on the enable_borrowed_range variable-template
// syntax when compiling as CUDA source; fixed in CUDA 12.2 (issue #3907)
#elif defined(__CUDACC__) && defined(__CUDACC_VER_MAJOR__) && __CUDACC_VER_MAJOR__ == 12 \
&& defined(__CUDACC_VER_MINOR__) && (__CUDACC_VER_MINOR__ == 0 || __CUDACC_VER_MINOR__ == 1)
#define JSON_HAS_RANGES 0
#elif defined(__cpp_lib_ranges)
#define JSON_HAS_RANGES 1
#else