Fix ci_cuda_example CUDA 11.8 build after C++17 fallback (#3907)

The 11.8.0 leg's graceful C++17 fallback (added in the previous commit)
worked correctly, but the broadened smoke test used the <=> operator
unconditionally, which isn't valid syntax pre-C++20 — nvcc rejected it
with "expected an expression" once the CMake logic picked cuda_std_17
for the older toolkit. Gate those two lines behind
JSON_HAS_THREE_WAY_COMPARISON like the library itself does internally.

Sanity-compiled the file as plain C++ at both -std=c++17 (skips the
guarded block) and -std=c++20 (includes it) locally; the actual nvcc
build is verified via CI on PR #5248.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

.github/dependabot.yml

@@ -4,6 +4,8 @@ updates:
     directory: /
     schedule:
       interval: daily
+    cooldown:
+      default-days: 7
     groups:
       codeql-action:
         patterns:
@@ -13,23 +15,33 @@ updates:
     directory: /docs/mkdocs
     schedule:
       interval: daily
+    cooldown:
+      default-days: 7
 
   - package-ecosystem: pip
     directory: /tools/astyle
     schedule:
       interval: daily
+    cooldown:
+      default-days: 7
 
   - package-ecosystem: pip
     directory: /tools/generate_natvis
     schedule:
       interval: daily
+    cooldown:
+      default-days: 7
 
   - package-ecosystem: pip
     directory: /tools/serve_header
     schedule:
       interval: daily
+    cooldown:
+      default-days: 7
 
   - package-ecosystem: pip
     directory: /cmake/requirements
     schedule:
       interval: daily
+    cooldown:
+      default-days: 7

.github/workflows/semgrep.yml

@@ -49,7 +49,7 @@ jobs:
       # SEMGREP_APP_TOKEN is still passed through so registry auth works if a
       # token is ever added.
       - name: Install Semgrep
-        run: python3 -m pip install --user semgrep
+        run: python3 -m pip install --user semgrep==1.168.0
 
       # `semgrep scan --sarif` always exits 0 even with findings; continue-on-error
       # is a safety net so the SARIF upload still runs if the scan itself errors.

.github/workflows/ubuntu.yml

@@ -234,11 +234,22 @@ jobs:
 
   ci_cuda_example:
     runs-on: ubuntu-latest
-    container: ghcr.io/nlohmann/json-ci:v2.4.0
+    strategy:
+      fail-fast: false
+      matrix:
+        # 11.8.0: newest pre-C++20 CUDA release, exercises the C++17 fallback
+        # path (tests/cuda_example/CMakeLists.txt picks the standard per nvcc
+        # version); 12.1.1: permanent regression guard for #3907 (nvcc 12.0/12.1
+        # choke on enable_borrowed_range at C++20, fixed in 12.2); 12.6.3: recent
+        # CUDA/C++20 coverage.
+        cuda: ['11.8.0', '12.1.1', '12.6.3']
+    container: nvidia/cuda:${{ matrix.cuda }}-devel-ubuntu22.04
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
+      - name: Get latest CMake and ninja
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build

.github/workflows/windows.yml

@@ -90,11 +90,13 @@ jobs:
       - name: Get latest CMake and ninja
         uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Set extra CXX_FLAGS for latest std_version
+        # /wd5285 silences C5285 emitted by the bundled third-party doctest.h, which
+        # specializes std::tuple (newly diagnosed by the VS2026 v145 toolset)
         run: |
           if [ "${{ matrix.std_version }}" = "latest" ]; then
-            echo "flags=/permissive- /std:c++latest /utf-8 /W4 /WX" >> $GITHUB_ENV
+            echo "flags=/permissive- /std:c++latest /utf-8 /W4 /WX /wd5285" >> $GITHUB_ENV
           else
-            echo "flags=/W4 /WX" >> $GITHUB_ENV
+            echo "flags=/W4 /WX /wd5285" >> $GITHUB_ENV
           fi
         shell: bash
       - name: Run CMake (Release)

cmake/ci.cmake

@@ -669,7 +669,6 @@ add_custom_target(ci_test_compiler_default
 add_custom_target(ci_cuda_example
     COMMAND ${CMAKE_COMMAND}
         -DCMAKE_BUILD_TYPE=Debug -GNinja
-        -DCMAKE_CUDA_HOST_COMPILER=g++-8
         -S${PROJECT_SOURCE_DIR}/tests/cuda_example -B${PROJECT_BINARY_DIR}/build_cuda_example
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_cuda_example
 )

cmake/clang_flags.cmake

@@ -5,7 +5,7 @@
 # -Wno-extra-semi-stmt            The library uses assert which triggers this warning.
 # -Wno-padded                     We do not care about padding warnings.
 # -Wno-covered-switch-default     All switches list all cases and a default case.
-# -Wno-unsafe-buffer-usage        Otherwise library code (strlen) would not compile.
+# -Wno-unsafe-buffer-usage        Otherwise Doctest would not compile.
 # -Wno-missing-noreturn           We found no way to silence this warning otherwise, see PR #4871
 
 set(CLANG_CXXFLAGS

cmake/gcc_flags.cmake

@@ -4,6 +4,7 @@
 # -Wno-aggregate-return  The library uses aggregate returns.
 # -Wno-long-long         The library uses the long long type to interface with system functions.
 # -Wno-namespaces        The library uses namespaces.
+# -Wno-nrvo              Doctest triggers this warning.
 # -Wno-padded            We do not care about padding warnings.
 # -Wno-system-headers    We do not care about warnings in system headers.
 # -Wno-templates         The library uses templates.
@@ -231,6 +232,7 @@ set(GCC_CXXFLAGS
     -Wnonnull
     -Wnonnull-compare
     -Wnormalized=nfkc
+    -Wno-nrvo
     -Wnull-dereference
     -Wodr
     -Wold-style-cast

docs/mkdocs/docs/community/quality_assurance.md

@@ -62,7 +62,9 @@ violations will result in a failed build.
         | Clang 20.1.1                                 | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
         | Clang 20.1.8 with GNU-like command-line      | x86_64       | Windows Server 2022 (Build 20348) | GitHub    |
         | Clang 21.1.8                                 | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
-        | CUDA 11.0.221 (nvcc)                         | x86_64       | Ubuntu 20.04 LTS                  | GitHub    |
+        | CUDA 11.8.0 (nvcc)                           | x86_64       | Ubuntu 22.04 LTS                  | GitHub    |
+        | CUDA 12.1.1 (nvcc)                           | x86_64       | Ubuntu 22.04 LTS                  | GitHub    |
+        | CUDA 12.6.3 (nvcc)                           | x86_64       | Ubuntu 22.04 LTS                  | GitHub    |
         | Emscripten 4.0.6                             | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
         | GNU 4.8.5                                    | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
         | GNU 4.9.3                                    | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |

include/nlohmann/detail/macro_scope.hpp

@@ -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

single_include/nlohmann/json.hpp

@@ -2520,6 +2520,11 @@ JSON_HEDLEY_DIAGNOSTIC_POP
         #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

tests/cuda_example/CMakeLists.txt

@@ -3,7 +3,18 @@ project(json_cuda LANGUAGES CUDA)
 
 add_executable(json_cuda json_cuda.cu)
 target_include_directories(json_cuda PRIVATE ../../include)
-target_compile_features(json_cuda PUBLIC cuda_std_11)
+
+# nvcc added C++20 support in CUDA 12.0 and C++17 in CUDA 11.0; pick the
+# newest standard the detected compiler actually supports (see #3907)
+# instead of hard-requiring one standard for every CUDA version.
+if(CMAKE_CUDA_COMPILER_VERSION VERSION_GREATER_EQUAL 12.0)
+    set(json_cuda_std 20)
+elseif(CMAKE_CUDA_COMPILER_VERSION VERSION_GREATER_EQUAL 11.0)
+    set(json_cuda_std 17)
+else()
+    set(json_cuda_std 11)
+endif()
+target_compile_features(json_cuda PUBLIC cuda_std_${json_cuda_std})
 set_target_properties(json_cuda PROPERTIES
     CUDA_EXTENSIONS OFF
     CUDA_STANDARD_REQUIRED ON

tests/cuda_example/json_cuda.cu

@@ -16,4 +16,20 @@ int main()
     // regression for #3013 (ordered_json::reset() compile error with nvcc)
     nlohmann::ordered_json metadata;
     metadata.erase("key");
+
+    // exercise comparisons (operator==/operator<=>, gated by
+    // JSON_HAS_THREE_WAY_COMPARISON, independent of JSON_HAS_RANGES) and
+    // range-based iteration (exercises iteration_proxy/ranges machinery
+    // beyond just the enable_borrowed_range specialization) — see #3907
+    nlohmann::json a = {1, 2, 3};
+    nlohmann::json b = {1, 2, 3};
+    static_cast<void>(a == b);
+#if JSON_HAS_THREE_WAY_COMPARISON
+    static_cast<void>(a <=> b); // *NOPAD*
+    static_cast<void>(a <=> 1); // *NOPAD*
+#endif
+    for (const auto& element : a)
+    {
+        static_cast<void>(element);
+    }
 }

tests/src/unit-algorithms.cpp

@@ -232,6 +232,9 @@ TEST_CASE("algorithms")
             // only the first four elements are expected to be sorted, the rest are
             // unspecified by the standard
             const json expected({nullptr, false, true, 3});
+            // std::equal below only bounds-checks the first range; assert the
+            // second range is at least as long to rule out an over-read (CWE-126)
+            CHECK(std::distance(begin(expected), end(expected)) >= 4);
             CHECK(std::equal(j.begin(), j.begin() + 4, begin(expected)));
         }
     }