build: Fallback to libc++ if clang does not support tuples as map keys

Workaround to avoid issue in clang 17
https://discourse.llvm.org/t/pack-expansion-bug/64910

Author: Gabrielcarvfer

build-support/cmake-format.yaml

@@ -64,6 +64,19 @@ additional_commands:
             PUBLIC_HEADER_FILES: '*'
             DEPRECATED_HEADER_FILES: '*'
             PRIVATE_HEADER_FILES: '*'
+    try_compile:
+        pargs:
+            nargs: 3
+        kwargs:
+            OUTPUT_VARIABLE: '1'
+            CXX_STANDARD: '1'
+            CXX_STANDARD_REQUIRED: '1'
+            CXX_EXTENSIONS: '1'
+            SOURCES: '*'
+            CMAKE_FLAGS: '*'
+            COMPILE_DEFINITIONS: '*'
+            LINK_OPTIONS: '*'
+            LINK_LIBRARIES: '*'
 
 format:
   tab_size: 2

build-support/custom-modules/ns3-compiler-workarounds.cmake

@@ -6,11 +6,52 @@
 
 include(CheckCXXSourceCompiles)
 
+# Some versions of clang (17) have issues with stdlibc++, so we check if we can
+# fallback to libc++ instead
+if(CLANG)
+  try_compile(
+    CLANG_STDLIBCPP_WORKS
+    SOURCES ${PROJECT_SOURCE_DIR}/build-support/test-clang17-stdlibcpp-map.cc
+    COMPILE_DEFINITIONS -stdlib=libstdc++
+    LINK_OPTIONS -stdlib=libstdc++
+    CXX_STANDARD 23
+    CXX_STANDARD_REQUIRED TRUE
+    CXX_EXTENSIONS FALSE
+  )
+
+  try_compile(
+    CLANG_LIBCPP_WORKS
+    SOURCES ${PROJECT_SOURCE_DIR}/build-support/test-clang17-stdlibcpp-map.cc
+    COMPILE_DEFINITIONS -stdlib=libc++
+    LINK_OPTIONS -stdlib=libc++
+    CXX_STANDARD 23
+    CXX_STANDARD_REQUIRED TRUE
+    CXX_EXTENSIONS FALSE
+  )
+  if((NOT ${CLANG_STDLIBCPP_WORKS}) AND (NOT ${CLANG_LIBCPP_WORKS}))
+    message(
+      FATAL_ERROR
+        "This clang version ${CMAKE_CXX_COMPILER_VERSION} is not compatible with using std::tuple as std::map keys"
+    )
+  elseif(${CLANG_STDLIBCPP_WORKS})
+    message(
+      STATUS
+        "This clang version ${CMAKE_CXX_COMPILER_VERSION} is compatible with using std::tuple as std::map keys"
+    )
+  else()
+    message(
+      ${HIGHLIGHTED_STATUS}
+      "This clang version ${CMAKE_CXX_COMPILER_VERSION} requires libc++ to use std::tuple as std::map keys"
+    )
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -stdlib=libc++")
+  endif()
+endif()
+
 # Some compilers (e.g. GCC <= 15) do not link std::stacktrace by default. If the
 # sample program can be linked, it means it is indeed linked by default.
 # Otherwise, we link it manually.
 # https://en.cppreference.com/w/cpp/header/stacktrace
-set(CMAKE_REQUIRED_FLAGS -std=c++23)
+set(CMAKE_REQUIRED_FLAGS ${CMAKE_CXX_FLAGS} -std=c++23)
 check_cxx_source_compiles(
   "
   #if __has_include(<stacktrace>)

build-support/test-clang17-stdlibcpp-map.cc

@@ -0,0 +1,12 @@
+#include <iostream>
+#include <map>
+#include <tuple>
+
+int
+main()
+{
+    std::map<std::tuple<int, int>, int> testMap;
+    testMap[{1, 1}] = 2;
+    std::cout << testMap.at({1, 1}) << std::endl;
+    return 0;
+}

utils/tests/gitlab-ci-clang.yml

@@ -18,6 +18,7 @@
     - apt upgrade -y
     - DEBIAN_FRONTEND=noninteractive apt install -y
       clang-$CLANG cmake ninja-build ccache build-essential
+      lld-$CLANG libc++-$CLANG-dev libc++abi-$CLANG-dev
       libboost-all-dev
       libeigen3-dev
       libgtk-3-0 libgtk-3-dev