Add support for C++26 (#5397)

Description of changes:
- remove array comparison deprecated in C++20 and removed in C++26 (P2865R6)
- support C++26's new `std::to_string` implementation
- bump Caliper version
- update CI runner images and C++ compiler toolchains and simplify CI/CD workflows

Author: jngrad

.github/actions/build_and_check/action.yml

@@ -9,7 +9,7 @@ permissions:
 
 jobs:
   deploy_docs:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     if: ${{ github.repository == 'espressomd/espresso' }}
     environment: deploy_documentation
     steps:

.github/workflows/deploy.yml

@@ -24,35 +24,42 @@ jobs:
       - name: Install dependencies
         run: |
          echo '' > Brewfile
-         for dep in boost boost-mpi libomp fftw gsl ccache ninja; do echo "brew \"${dep}\"" >> Brewfile; done
+         for dep in boost boost-mpi libomp fftw gsl ccache ninja hdf5-mpi; do echo "brew \"${dep}\"" >> Brewfile; done
          brew bundle check >/dev/null 2>&1 || brew bundle --verbose --no-upgrade
          # set up Xcode compiler
          echo "::group::List available Xcode compilers"
          ls /Applications | grep Xcode
          echo "::endgroup::"
-         sudo xcode-select -switch /Applications/Xcode_26.2.0.app
+         sudo xcode-select -switch /Applications/Xcode_26.6.0.app
          # Python dependencies
          python -m venv venv
          . venv/bin/activate
          python -m pip install -c requirements.txt cython numpy scipy packaging
          deactivate
         shell: bash
       - name: Build and check
-        uses: ./.github/actions/build_and_check
+        run: |
+         if test -d venv; then . venv/bin/activate; fi
+         bash maintainer/CI/build_cmake.sh
         env:
           build_procs: 3
           check_procs: 3
           cmake_params: '-D ESPRESSO_TEST_NP=3'
+          myconfig: 'maxset'
           with_ccache: 'true'
+          with_cuda: 'false'
+          with_hdf5: 'true'
           with_fftw: 'true'
           with_gsl: 'true'
           with_walberla: 'true'
           with_walberla_avx: 'false'
+          check_skip_long: 'true'
+          test_timeout: 800
 
   debian:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     container:
-      image: ghcr.io/espressomd/docker/debian:ab5bc64f5c3cc7330952f8b3bf321270ca53960c-base-layer
+      image: ghcr.io/espressomd/docker/debian:c6ad9809eed1d0e9f26f4968559b234ea3b8bf82-base-layer
       credentials:
          username: ${{ github.actor }}
          password: ${{ secrets.github_token }}
@@ -70,7 +77,9 @@ jobs:
       - name: Get runner specifications
         run: lscpu | egrep 'Model name|Socket|Thread|NUMA|CPU\(s\)'
       - name: Build and check
-        uses: ./.github/actions/build_and_check
+        run: |
+         if test -d venv; then . venv/bin/activate; fi
+         bash maintainer/CI/build_cmake.sh
         env:
           build_procs: 4
           check_procs: 4
@@ -90,10 +99,10 @@ jobs:
           OMPI_ALLOW_RUN_AS_ROOT_CONFIRM: 1
 
   ubuntu:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     if: ${{ github.repository == 'espressomd/espresso' }}
     container:
-      image: ghcr.io/espressomd/docker/ubuntu-wo-dependencies:ab5bc64f5c3cc7330952f8b3bf321270ca53960c-base-layer
+      image: ghcr.io/espressomd/docker/ubuntu-wo-dependencies:c6ad9809eed1d0e9f26f4968559b234ea3b8bf82-base-layer
       credentials:
          username: ${{ github.actor }}
          password: ${{ secrets.github_token }}
@@ -111,12 +120,14 @@ jobs:
       - name: Get runner specifications
         run: lscpu | egrep 'Model name|Socket|Thread|NUMA|CPU\(s\)'
       - name: Build and check
-        uses: ./.github/actions/build_and_check
+        run: |
+         if test -d venv; then . venv/bin/activate; fi
+         bash maintainer/CI/build_cmake.sh
         env:
           build_procs: 4
           check_procs: 4
-          CC: 'gcc-13'
-          CXX: 'g++-13'
+          CC: 'gcc-16'
+          CXX: 'g++-16'
           myconfig: 'maxset'
           with_ccache: 'true'
           with_cuda: 'false'
@@ -132,10 +143,10 @@ jobs:
           OMPI_ALLOW_RUN_AS_ROOT_CONFIRM: 1
 
   fedora:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     if: ${{ github.repository == 'espressomd/espresso' }}
     container:
-      image: ghcr.io/espressomd/docker/fedora:ab5bc64f5c3cc7330952f8b3bf321270ca53960c-base-layer
+      image: ghcr.io/espressomd/docker/fedora:c6ad9809eed1d0e9f26f4968559b234ea3b8bf82-base-layer
       credentials:
          username: ${{ github.actor }}
          password: ${{ secrets.github_token }}
@@ -153,7 +164,9 @@ jobs:
       - name: Get runner specifications
         run: lscpu | egrep 'Model name|Socket|Thread|NUMA|CPU\(s\)'
       - name: Build and check
-        uses: ./.github/actions/build_and_check
+        run: |
+         if test -d venv; then . venv/bin/activate; fi
+         bash maintainer/CI/build_cmake.sh
         env:
           build_procs: 4
           check_procs: 4
@@ -170,4 +183,6 @@ jobs:
           with_walberla: 'true'
           with_walberla_avx: 'false'
           with_stokesian_dynamics: 'true'
-          cmake_params: '-D CMAKE_CXX_STANDARD=23 -D CMAKE_INCLUDE_PATH=/usr/include/mpich-x86_64 -D CMAKE_PREFIX_PATH=/usr/lib64/mpich/lib/ -D ESPRESSO_TEST_NT=1'
+          check_skip_long: 'true'
+          test_timeout: 800
+          cmake_params: '-D CMAKE_CXX_STANDARD=26 -D CMAKE_INCLUDE_PATH=/usr/include/mpich-x86_64 -D CMAKE_PREFIX_PATH=/usr/lib64/mpich/lib/ -D ESPRESSO_TEST_NT=1'

.github/workflows/push_pull.yml

@@ -1,4 +1,4 @@
-image: ghcr.io/espressomd/docker/ubuntu:ab5bc64f5c3cc7330952f8b3bf321270ca53960c
+image: ghcr.io/espressomd/docker/ubuntu:c6ad9809eed1d0e9f26f4968559b234ea3b8bf82
 
 stages:
   - prepare
@@ -16,7 +16,7 @@ stages:
 
 .notification_job_template: &notification_job_definition
   <<: *global_job_definition
-  image: ghcr.io/espressomd/docker/alpine:ab5bc64f5c3cc7330952f8b3bf321270ca53960c
+  image: ghcr.io/espressomd/docker/alpine:c6ad9809eed1d0e9f26f4968559b234ea3b8bf82
   variables:
     GET_SOURCES_ATTEMPTS: 3
   dependencies: []

.gitlab-ci.yml

@@ -1035,7 +1035,7 @@ if(ESPRESSO_BUILD_WITH_WALBERLA)
     # cmake-format: off
     FetchContent_Declare(
       walberla
-      GIT_REPOSITORY https://i10git.cs.fau.de/walberla/walberla.git
+      GIT_REPOSITORY https://github.com/lssfau/walberla.git
       GIT_TAG        3247aa73 # v7.2 with patches
     )
     # cmake-format: on
@@ -1108,7 +1108,7 @@ if(ESPRESSO_BUILD_WITH_CALIPER)
   FetchContent_Declare(
     caliper
     GIT_REPOSITORY https://github.com/LLNL/Caliper.git
-    GIT_TAG        v2.14.0
+    GIT_TAG        v2.15.0
   )
   # cmake-format: on
   set(CALIPER_OPTION_PREFIX on CACHE BOOL "")

CMakeLists.txt

@@ -22,6 +22,8 @@
 
 #include "script_interface/auto_parameters/AutoParameters.hpp"
 
+#include <algorithm>
+#include <string_view>
 #include <variant>
 
 using ScriptInterface::AutoParameters;
@@ -34,13 +36,14 @@ struct A : AutoParameters<A> {
 };
 
 BOOST_AUTO_TEST_CASE(basic) {
+  using namespace std::literals;
   A a{0, 42};
 
   auto const &parameters = a.valid_parameters();
 
   BOOST_CHECK(parameters.size() == 2u);
-  BOOST_CHECK(std::ranges::find(parameters, "i") != parameters.end());
-  BOOST_CHECK(std::ranges::find(parameters, "j") != parameters.end());
+  BOOST_CHECK(std::ranges::find(parameters, "i"sv) != parameters.end());
+  BOOST_CHECK(std::ranges::find(parameters, "j"sv) != parameters.end());
 
   BOOST_CHECK(0 == std::get<int>(a.get_parameter("i")));
   BOOST_CHECK(42 == std::get<int>(a.get_parameter("j")));

src/script_interface/tests/AutoParameters_test.cpp

@@ -73,7 +73,7 @@ def test_runtime_report(self):
             if not line.startswith("WARNING:"):
                 lines = lines[i:]
                 break
-        header = "Path\tMin time/rank\tMax time/rank\tAvg time/rank\tTime %"
+        header = "Path\tMin time/rank\tAvg time/rank\tMax time/rank\tTime %"
         self.assertEqual(lines[0].split(), header.split(),
                          msg=f"Caliper summary should start with '{header}'")
         labels = [line[:36].rstrip() for line in lines[1:]]

testsuite/python/caliper.py

@@ -273,7 +273,7 @@ def test_temperature_change(self):
         self.system.thermostat.set_langevin(kT=1., gamma=1., seed=42)
         self.system.thermostat.set_langevin(kT=2., gamma=1., seed=42)
         self.system.thermostat.set_brownian(kT=2., gamma=1., seed=42)
-        with self.assertRaisesRegex(RuntimeError, "Cannot set parameter 'kT' to 1.0*: there are currently active thermostats with kT=2.0*"):
+        with self.assertRaisesRegex(RuntimeError, "Cannot set parameter 'kT' to 1[.0]*: there are currently active thermostats with kT=2[.0]*"):
             self.system.thermostat.set_brownian(kT=1., gamma=1., seed=42)
         with self.assertRaisesRegex(RuntimeError, f"Parameter 'kT' is read-only"):
             self.system.thermostat.kT = 2.

testsuite/python/integrator_exceptions.py

@@ -508,7 +508,7 @@ def test_temperature_mismatch(self):
         self.system.thermostat.set_langevin(kT=2., seed=23, gamma=2.)
         lbf = self.lb_class(kT=1., seed=42, **self.params, **self.lb_params)
         self.system.lb = lbf
-        with self.assertRaisesRegex(RuntimeError, "Cannot set parameter 'kT' to 1.0*: there are currently active thermostats with kT=2.0*"):
+        with self.assertRaisesRegex(RuntimeError, r"Cannot set parameter 'kT' to (1[.0]*|0\.99[0-9]+): there are currently active thermostats with kT=(2[.0]*|1\.99[0-9]+)"):
             self.system.thermostat.set_lb(LB_fluid=lbf, seed=23, gamma=2.)
         self.assertFalse(self.system.thermostat.lb.is_active)
         self.assertTrue(self.system.thermostat.langevin.is_active)
@@ -869,9 +869,9 @@ def params_with_tau(tau):
             self.lb_class(**params_with_tau(self.system.time_step),
                           **self.lb_params)
 
-        with self.assertRaisesRegex(ValueError, r"LB tau \(0\.0100[0-9]+\) must be >= MD time_step \(0\.0200[0-9]+\)"):
+        with self.assertRaisesRegex(ValueError, r"LB tau \(0\.01(?:0*|00[0-9]+)\) must be >= MD time_step \(0\.02(?:0*|00[0-9]+)\)"):
             self.system.time_step = 2.0 * lbf.get_params()["tau"]
-        with self.assertRaisesRegex(ValueError, r"LB tau \(0\.0100[0-9]+\) must be an integer multiple of the MD time_step \(0\.0080[0-9]+\)"):
+        with self.assertRaisesRegex(ValueError, r"LB tau \(0\.01(?:0*|00[0-9]+)\) must be an integer multiple of the MD time_step \(0\.008(?:0*|0[0-9]+)\)"):
             self.system.time_step = 0.8 * lbf.get_params()["tau"]
 
         self.system.lb = None

testsuite/python/lb.py

@@ -349,15 +349,15 @@ def test_exceptions(self):
         with self.assertRaisesRegex(ValueError, "Invalid value for 'exclusion_range'"):
             espressomd.reaction_methods.ReactionEnsemble(
                 kT=1., seed=12, exclusion_range=-1.)
-        with self.assertRaisesRegex(ValueError, "Invalid excluded_radius value for type 1: radius -0.10"):
+        with self.assertRaisesRegex(ValueError, r"Invalid excluded_radius value for type 1: radius -0\.1[0]*"):
             espressomd.reaction_methods.ReactionEnsemble(
                 kT=1., seed=12, exclusion_range=1., exclusion_radius_per_type={1: -0.1})
         with self.assertRaisesRegex(ValueError, "Unknown search algorithm 'unknown'"):
             espressomd.reaction_methods.ReactionEnsemble(
                 kT=1., seed=12, exclusion_range=1., search_algorithm="unknown")
         method = espressomd.reaction_methods.ReactionEnsemble(
             kT=1., exclusion_range=1., seed=12, exclusion_radius_per_type={1: 0.1})
-        with self.assertRaisesRegex(ValueError, "Invalid excluded_radius value for type 2: radius -0.10"):
+        with self.assertRaisesRegex(ValueError, r"Invalid excluded_radius value for type 2: radius -0\.1[0]*"):
             method.exclusion_radius_per_type = {2: -0.1}
         self.assertEqual(list(method.exclusion_radius_per_type.keys()), [1])