Add CI build for next C++ version

.github/workflows/main.yml

@@ -147,3 +147,11 @@ jobs:
       - uses: actions/checkout@v3
       - name: 'Unsigned Char Tests'
         run: build-scripts/test-unsigned-char
+  CxxNext:
+    runs-on: ubuntu-latest
+    # Build after Fuzzers to save concurrent runners
+    needs: Fuzzers
+    steps:
+      - uses: actions/checkout@v3
+      - name: 'Build with Next C++ standard'
+        run: build-scripts/test-c++-next

CMakeLists.txt

@@ -106,6 +106,7 @@ option(INSTALL_CMAKE_PACKAGE "Install cmake package files" ON)
 option(INSTALL_EXAMPLES "Install example files" ON)
 
 option(FUTURE "Include ABI-breaking changes CONSIDERED for the next major release" OFF)
+option(CXX_NEXT "Build with next C++ standard version" OFF)
 
 # *** END OPTIONS ***
 
@@ -166,7 +167,11 @@ Please build with cmake in a subdirectory, e.g.
 Please remove CMakeCache.txt and the CMakeFiles directories.")
 endif()
 
-set(CMAKE_CXX_STANDARD 17)
+if(CXX_NEXT)
+  set(CMAKE_CXX_STANDARD 20)
+else()
+  set(CMAKE_CXX_STANDARD 17)
+endif()
 set(CMAKE_CXX_EXTENSIONS OFF)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_C_VISIBILITY_PRESET hidden)

build-scripts/test-c++-next

@@ -0,0 +1,14 @@
+#!/bin/bash
+set -e
+sudo apt-get update
+sudo apt-get -y install \
+   build-essential cmake \
+   zlib1g-dev libjpeg-dev libgnutls28-dev libssl-dev
+cmake -S . -B build \
+    -DCXX_NEXT=ON \
+    -DCI_MODE=1 -DBUILD_STATIC_LIBS=0 -DCMAKE_BUILD_TYPE=Release \
+    -DREQUIRE_CRYPTO_OPENSSL=1 -DREQUIRE_CRYPTO_GNUTLS=1 \
+    -DENABLE_QTC=1
+cmake --build build --verbose -j$(nproc) -- -k
+cd build
+ctest --verbose