Require C++20 for building tests since that's what mettle requires

.github/workflows/build.yml

@@ -24,10 +24,6 @@ jobs:
       matrix:
         include:
           # GCC builds
-          - {os: ubuntu-20.04,  compiler: gcc, version:  '8',
-             flags: '-Wsuggest-override', options: '--with-boost-filesystem'}
-          - {os: ubuntu-latest, compiler: gcc, version:  '9',
-             flags: '-Wsuggest-override'}
           - {os: ubuntu-latest, compiler: gcc, version: '10',
              flags: '-Wsuggest-override'}
           - {os: ubuntu-latest, compiler: gcc, version: '11',
@@ -36,35 +32,34 @@ jobs:
              flags: '-Wsuggest-override'}
           - {os: ubuntu-latest, compiler: gcc, version: '13',
              flags: '-Wsuggest-override'}
+          - {os: ubuntu-24.04,  compiler: gcc, version: '14',
+             flags: '-Wsuggest-override'}
 
           # Clang builds
-          - {os: ubuntu-20.04,  compiler: clang, version:  '9'}
           - {os: ubuntu-20.04,  compiler: clang, version: '10'}
           - {os: ubuntu-20.04,  compiler: clang, version: '11'}
           - {os: ubuntu-20.04,  compiler: clang, version: '12'}
           - {os: ubuntu-latest, compiler: clang, version: '13'}
           - {os: ubuntu-latest, compiler: clang, version: '14'}
           - {os: ubuntu-latest, compiler: clang, version: '15'}
           - {os: ubuntu-latest, compiler: clang, version: '16'}
+          - {os: ubuntu-latest, compiler: clang, version: '17'}
+          - {os: ubuntu-latest, compiler: clang, version: '18'}
 
           # Windows builds
-          - {os: windows-2019,   compiler: msvc, version: '14.1',  # VS 2017
-             boost-version: '1.80.0'}
-          - {os: windows-2019,   compiler: msvc, version: '14.2',  # VS 2019
-             boost-version: '1.80.0'}
           - {os: windows-latest, compiler: msvc, version: '14.4',  # VS 2022
              boost-version: '1.80.0'}
 
           # macOS builds
           - {os: macos-latest, compiler: clang}
 
-          # C++20 builds
-          - {os: ubuntu-latest, compiler: gcc, version: '13',
-             common-options: '--std=c++20', flags: '-Wsuggest-override',
-             boost-version: '1.78.0', extra-desc: 'c++20'}
-          - {os: ubuntu-latest, compiler: clang, version: '16',
-             common-options: '--std=c++20', boost-version: '1.78.0',
-             extra-desc: 'c++20'}
+          # C++23 builds
+          - {os: ubuntu-24.04, compiler: gcc, version: '14',
+             common-options: '--std=c++23', flags: '-Wsuggest-override',
+             boost-version: '1.85.0', extra-desc: 'c++20'}
+          - {os: ubuntu-latest, compiler: clang, version: '18',
+             common-options: '--std=c++20', boost-version: '1.85.0',
+             extra-desc: 'c++23'}
       fail-fast: false
 
     steps:

options.bfg

@@ -1,4 +1,4 @@
 # -*- mode: python; mode: bfg9000-options -*-
 
-argument('std', default='c++17', help='set the C++ standard to compile with')
+argument('std', default='c++20', help='set the C++ standard to compile with')
 argument('boost-filesystem', action='with', help='use boost::filesystem')