Allow c++17 as cxxstd

.gitlab-ci.yml

@@ -67,12 +67,17 @@ default:
 juggler:local:
   image: eicweb.phy.anl.gov:4567/containers/eic_container/jug_xl:nightly
   stage: build
+  parallel:
+    matrix:
+    - CMAKE_CXX_STANDARD:
+      - 17
+      - 20
   script:
     ## first install EICD to ensure the latest version, then build juggler
     - |
       git clone https://eicweb.phy.anl.gov/eic/eicd.git /tmp/eicd
       cd /tmp/eicd && git checkout $JUGGLER_EICD_VERSION && cd -
-      cmake -B /tmp/build -S /tmp/eicd -DCMAKE_INSTALL_PREFIX=/usr/local
+      cmake -B /tmp/build -S /tmp/eicd -DCMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD} -DCMAKE_INSTALL_PREFIX=/usr/local
       cmake --build /tmp/build -j40 -- install
       rm -rf /tmp/build /tmp/eicd
     - |

CMakeLists.txt

@@ -5,7 +5,12 @@ cmake_policy(SET CMP0074 NEW)
 
 project(Juggler VERSION 4.3.0)
 
-set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD 20 CACHE STRING "")
+if(NOT CMAKE_CXX_STANDARD MATCHES "17|20")
+  message(FATAL_ERROR "Unsupported C++ standard: ${CMAKE_CXX_STANDARD}")
+endif()
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)
 
 # Export compile commands as json for run-clang-tidy
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)