Implement policy for Python, C++, and CMake versions (#3035)

.github/workflows/ci.yml

@@ -35,12 +35,6 @@ jobs:
         vectfit: [n]
 
         include:
-          - python-version: "3.8"
-            omp: n
-            mpi: n
-          - python-version: "3.9"
-            omp: n
-            mpi: n
           - python-version: "3.11"
             omp: n
             mpi: n

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.16 FATAL_ERROR)
 project(openmc C CXX)
 
 # Set version numbers
@@ -16,11 +16,6 @@ set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
 # Set module path
 set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules)
 
-# Allow user to specify <project>_ROOT variables
-if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.12)
-  cmake_policy(SET CMP0074 NEW)
-endif()
-
 # Enable correct usage of CXX_EXTENSIONS
 if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.22)
   cmake_policy(SET CMP0128 NEW)
@@ -272,11 +267,6 @@ endif()
 # xtensor header-only library
 #===============================================================================
 
-# CMake 3.13+ will complain about policy CMP0079 unless it is set explicitly
-if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.13)
-  cmake_policy(SET CMP0079 NEW)
-endif()
-
 find_package_write_status(xtensor)
 if (NOT xtensor_FOUND)
   add_subdirectory(vendor/xtl)
@@ -580,9 +570,9 @@ target_compile_options(openmc PRIVATE ${cxxflags})
 target_include_directories(openmc PRIVATE ${CMAKE_BINARY_DIR}/include)
 target_link_libraries(openmc libopenmc)
 
-# Ensure C++14 standard is used and turn off GNU extensions
-target_compile_features(openmc PUBLIC cxx_std_14)
-target_compile_features(libopenmc PUBLIC cxx_std_14)
+# Ensure C++17 standard is used and turn off GNU extensions
+target_compile_features(openmc PUBLIC cxx_std_17)
+target_compile_features(libopenmc PUBLIC cxx_std_17)
 set_target_properties(openmc libopenmc PROPERTIES CXX_EXTENSIONS OFF)
 
 #===============================================================================

docs/source/devguide/index.rst

@@ -15,6 +15,7 @@ other related topics.
     contributing
     workflow
     styleguide
+    policies
     tests
     user-input
     docbuild

docs/source/devguide/policies.rst

@@ -0,0 +1,35 @@
+.. _devguide_policies:
+
+========
+Policies
+========
+
+---------------------
+Python Version Policy
+---------------------
+
+OpenMC follows the Scientific Python Ecosystem Coordination guidelines `SPEC 0
+<https://scientific-python.org/specs/spec-0000/>`_ on minimum supported
+versions, which recommends that support for Python versions be dropped 3 years
+after their initial release.
+
+-------------------
+C++ Standard Policy
+-------------------
+
+C++ code in OpenMC must conform to the most recent C++ standard that is fully
+supported in the `version of the gcc compiler
+<https://gcc.gnu.org/projects/cxx-status.html>`_ that is distributed with the
+oldest version of Ubuntu that is still within its `standard support period
+<https://ubuntu.com/about/release-cycle>`_. Ubuntu 20.04 LTS will be supported
+through April 2025 and is distributed with gcc 9.3.0, which fully supports the
+C++17 standard.
+
+--------------------
+CMake Version Policy
+--------------------
+
+Similar to the C++ standard policy, the minimum supported version of CMake
+corresponds to whatever version is distributed with the oldest version of Ubuntu
+still within its standard support period. Ubuntu 20.04 LTS is distributed with
+CMake 3.16.

docs/source/devguide/styleguide.rst

@@ -40,7 +40,7 @@ Follow the `C++ Core Guidelines`_ except when they conflict with another
 guideline listed here. For convenience, many important guidelines from that
 list are repeated here.
 
-Conform to the C++14 standard.
+Conform to the C++17 standard.
 
 Always use C++-style comments (``//``) as opposed to C-style (``/**/``). (It
 is more difficult to comment out a large section of code that uses C-style

examples/custom_source/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.16 FATAL_ERROR)
 project(openmc_sources CXX)
 add_library(source SHARED source_ring.cpp)
 find_package(OpenMC REQUIRED)

examples/parameterized_custom_source/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.16 FATAL_ERROR)
 project(openmc_sources CXX)
 add_library(parameterized_source SHARED parameterized_source_ring.cpp)
 find_package(OpenMC REQUIRED)

setup.py

@@ -53,15 +53,13 @@ kwargs = {
         'Topic :: Scientific/Engineering'
         'Programming Language :: C++',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.8',
-        'Programming Language :: Python :: 3.9',
         'Programming Language :: Python :: 3.10',
         'Programming Language :: Python :: 3.11',
         'Programming Language :: Python :: 3.12',
     ],
 
     # Dependencies
-    'python_requires': '>=3.8',
+    'python_requires': '>=3.10',
     'install_requires': [
         'numpy>=1.9', 'h5py', 'scipy', 'ipython', 'matplotlib',
         'pandas', 'lxml', 'uncertainties', 'setuptools'

tests/regression_tests/deplete_with_transfer_rates/test.py

@@ -46,7 +46,6 @@ def model():
 
     return openmc.Model(geometry, materials, settings)
 
-@pytest.mark.skipif(sys.version_info < (3, 9), reason="Requires Python 3.9+")
 @pytest.mark.parametrize("rate, dest_mat, power, ref_result", [
     (1e-5, None, 0.0, 'no_depletion_only_removal'),
     (-1e-5, None, 0.0, 'no_depletion_only_feed'),

tests/unit_tests/test_data_photon.py

@@ -121,8 +121,6 @@ def test_reactions(element, reaction):
         reactions[18]
 
 
-# TODO: Remove skip when support is Python 3.9+
-@pytest.mark.skipif(not hasattr(pd.options, 'future'), reason='pandas version too old')
 @pytest.mark.parametrize('element', ['Pu'], indirect=True)
 def test_export_to_hdf5(tmpdir, element):
     filename = str(tmpdir.join('tmp.h5'))