Thread PYBIND11_NUMPY2_SUPPORT through things and try to adept test…

… matrix

.github/workflows/ci.yml

@@ -108,12 +108,14 @@ jobs:
       run: python -m pip install pytest-github-actions-annotate-failures
 
     # First build - C++11 mode and inplace
-    # More-or-less randomly adding -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON here.
+    # More-or-less randomly adding -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON here
+    # (same for PYBIND11_NUMPY2_SUPPORT).
     - name: Configure C++11 ${{ matrix.args }}
       run: >
         cmake -S . -B .
         -DPYBIND11_WERROR=ON
         -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON
+        -DPYBIND11_NUMPY2_SUPPORT=ON
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=11
@@ -138,11 +140,13 @@ jobs:
 
     # Second build - C++17 mode and in a build directory
     # More-or-less randomly adding -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF here.
+    # (same for PYBIND11_NUMPY2_SUPPORT, but requires a NumPy 1.x at runtime).
     - name: Configure C++17
       run: >
         cmake -S . -B build2
         -DPYBIND11_WERROR=ON
         -DPYBIND11_SIMPLE_GIL_MANAGEMENT=OFF
+        -DPYBIND11_NUMPY2_SUPPORT=OFF
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=17
@@ -895,8 +899,10 @@ jobs:
         python-version: ${{ matrix.python }}
 
     - name: Prepare env
+      # Ensure use of NumPy 2 (via NumPy nightlies but can be changed soon)
       run: |
-        python3 -m pip install -r tests/requirements.txt
+        python3 -m pip install -r tests/requirements.txt\
+        python3 -m pip install --upgrade --pre -i https://pypi.anaconda.org/scientific-python-nightly-wheels/simple numpy
 
     - name: Update CMake
       uses: jwlawson/actions-setup-cmake@v2.0
@@ -925,6 +931,7 @@ jobs:
       run: >
         cmake -S . -B build_partial
         -DPYBIND11_WERROR=ON
+        -DPYBIND11_
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=20

CMakeLists.txt

@@ -109,13 +109,17 @@ option(PYBIND11_TEST "Build pybind11 test suite?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_NOPYTHON "Disable search for Python" OFF)
 option(PYBIND11_SIMPLE_GIL_MANAGEMENT
        "Use simpler GIL management logic that does not support disassociation" OFF)
+option(PYBIND11_NUMPY2_SUPPORT "Enable compile in a NumPy 2 and 1 compatible way" OFF)
 set(PYBIND11_INTERNALS_VERSION
     ""
     CACHE STRING "Override the ABI version, may be used to enable the unstable ABI.")
 
 if(PYBIND11_SIMPLE_GIL_MANAGEMENT)
   add_compile_definitions(PYBIND11_SIMPLE_GIL_MANAGEMENT)
 endif()
+if(PYBIND11_NUMPY2_SUPPORT)
+  add_compile_definitions(PYBIND11_NUMPY2_SUPPORT)
+endif()
 
 cmake_dependent_option(
   USE_PYTHON_INCLUDE_DIR

include/pybind11/numpy.h

@@ -171,9 +171,9 @@ PYBIND11_NOINLINE module_ import_numpy_core_submodule(const char *submodule_name
 
 #ifndef PYBIND11_NUMPY2_SUPPORT
     if (major_version >= 2) {
-        throw std::runtime_error("module compiled without NumPy 2 support. Please "
-                                 "define PYBIND11_NUMPY2_SUPPORT before the `numpy2.h` "
-                                 "to enable it.");
+        throw std::runtime_error("module compiled without NumPy 2 support. Please define "
+                                 "PYBIND11_NUMPY2_SUPPORT before including `numpy2.h` "
+                                 "or define it during build to enable NumPy 2 support.");
     }
 #endif
     /* `numpy.core` was renamed to `numpy._core` in NumPy 2.0 as it officially

tests/conftest.py

@@ -218,4 +218,5 @@ def pytest_report_header(config):
         f" {pybind11_tests.cpp_std}"
         f" {pybind11_tests.PYBIND11_INTERNALS_ID}"
         f" PYBIND11_SIMPLE_GIL_MANAGEMENT={pybind11_tests.PYBIND11_SIMPLE_GIL_MANAGEMENT}"
+        f" PYBIND11_NUMPY2_SUPPORT={pybind11_tests.PYBIND11_NUMPY2_SUPPORT}"
     )

tests/pybind11_tests.cpp

@@ -95,6 +95,12 @@ PYBIND11_MODULE(pybind11_tests, m) {
 #else
         false;
 #endif
+    m.attr("PYBIND11_NUMPY2_SUPPORT") =
+#if defined(PYBIND11_NUMPY2_SUPPORT)
+        true;
+#else
+        false;
+#endif
 
     bind_ConstructorStats(m);
 

tests/test_numpy_dtypes.py

@@ -3,6 +3,7 @@
 import pytest
 
 import env  # noqa: F401
+from pybind11_tests import PYBIND11_NUMPY2_SUPPORT
 from pybind11_tests import numpy_dtypes as m
 
 np = pytest.importorskip("numpy")
@@ -178,7 +179,12 @@ def test_dtype(simple_dtype):
     assert m.test_dtype_num() == [np.dtype(ch).num for ch in expected_chars]
     assert m.test_dtype_byteorder() == [np.dtype(ch).byteorder for ch in expected_chars]
     assert m.test_dtype_alignment() == [np.dtype(ch).alignment for ch in expected_chars]
-    assert m.test_dtype_flags() == [np.dtype(ch).flags for ch in expected_chars]
+    if PYBIND11_NUMPY2_SUPPORT:
+        assert m.test_dtype_flags() == [np.dtype(ch).flags for ch in expected_chars]
+    else:
+        assert m.test_dtype_flags() == [
+            chr(np.dtype(ch).flags) for ch in expected_chars
+        ]
 
 
 def test_recarray(simple_dtype, packed_dtype):