[RFC] Remove support for building C++ with `LLVM_ENABLE_PROJECTS`

This has been officially deprecated since D112724, meaning the
deprecation warning is present in released 14 and 15.

This makes me think that now, shortly after the 15 release is branched,
is a good time to pull the trigger.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D132324

clang/lib/Driver/ToolChains/Linux.cpp

@@ -307,13 +307,6 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
 
   Generic_GCC::AddMultiarchPaths(D, SysRoot, OSLibDir, Paths);
 
-  // The deprecated -DLLVM_ENABLE_PROJECTS=libcxx configuration installs
-  // libc++.so in D.Dir+"/../lib/". Detect this path.
-  // TODO Remove once LLVM_ENABLE_PROJECTS=libcxx is unsupported.
-  if (StringRef(D.Dir).startswith(SysRoot) &&
-      D.getVFS().exists(D.Dir + "/../lib/libc++.so"))
-    addPathIfExists(D, D.Dir + "/../lib", Paths);
-
   addPathIfExists(D, concat(SysRoot, "/lib"), Paths);
   addPathIfExists(D, concat(SysRoot, "/usr/lib"), Paths);
 }

compiler-rt/lib/sanitizer_common/symbolizer/scripts/build_symbolizer.sh

@@ -100,12 +100,12 @@ if [[ ! -d ${LIBCXX_BUILD} ]]; then
   mkdir -p ${LIBCXX_BUILD}
   cd ${LIBCXX_BUILD}
   LIBCXX_FLAGS="${FLAGS} -Wno-macro-redefined"
-  PROJECTS=
+  RUNTIMES=
   if [[ ! -d $LLVM_SRC/projects/libcxxabi ]] ; then
-    PROJECTS="-DLLVM_ENABLE_PROJECTS='libcxx;libcxxabi'"
+    RUNTIMES="-DLLVM_ENABLE_RUNTIMES='libcxx;libcxxabi'"
   fi
   cmake -GNinja \
-    ${PROJECTS} \
+    ${RUNTIMES} \
     -DCMAKE_BUILD_TYPE=Release \
     -DCMAKE_C_COMPILER=$CC \
     -DCMAKE_CXX_COMPILER=$CXX \

libcxx/utils/ci/buildkite-pipeline.yml

@@ -321,20 +321,6 @@ steps:
             limit: 2
       timeout_in_minutes: 120
 
-    - label: "Legacy LLVM_ENABLE_PROJECTS build"
-      command: "libcxx/utils/ci/run-buildbot legacy-project-build"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
   # Tests with various build configurations.
   - label: "Static libraries"
     command: "libcxx/utils/ci/run-buildbot generic-static"

libcxx/utils/ci/oss-fuzz.sh

@@ -13,7 +13,7 @@ INSTALL=cxx_install_dir
 
 mkdir ${BUILD}
 cmake -S ${PWD} -B ${BUILD} \
-      -DLLVM_ENABLE_PROJECTS="libcxx;libcxxabi" \
+      -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
       -DCMAKE_BUILD_TYPE=RelWithDebInfo \
       -DCMAKE_INSTALL_PREFIX="${INSTALL}"
 cmake --build ${BUILD} --target install-cxx-headers

libcxx/utils/ci/run-buildbot

@@ -510,21 +510,6 @@ legacy-test-config)
                    -DLIBUNWIND_TEST_CONFIG="${MONOREPO_ROOT}/libunwind/test/lit.site.cfg.in"
     check-runtimes
 ;;
-legacy-project-build)
-    clean
-
-    echo "--- Generating CMake"
-    ${CMAKE} \
-          -S "${MONOREPO_ROOT}/llvm" \
-          -B "${BUILD_DIR}" \
-          -DLLVM_ENABLE_PROJECTS="libcxx;libunwind;libcxxabi" \
-          -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
-          -DCMAKE_BUILD_TYPE=RelWithDebInfo \
-          -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
-          -DLLVM_LIT_ARGS="-sv --show-unsupported --xunit-xml-output test-results.xml --timeout=1500" \
-          -DLIBCXX_CXX_ABI=libcxxabi
-    check-runtimes
-;;
 aarch64)
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/AArch64.cmake"

llvm/CMakeLists.txt

@@ -123,8 +123,9 @@ foreach(proj ${LLVM_ENABLE_PROJECTS})
 endforeach()
 foreach(proj "libcxx" "libcxxabi" "libunwind")
   if (${proj} IN_LIST LLVM_ENABLE_PROJECTS)
-    message(WARNING "Using LLVM_ENABLE_PROJECTS=${proj} is deprecated now, please use -DLLVM_ENABLE_RUNTIMES=${proj} or "
-                    "see the instructions at https://libcxx.llvm.org/BuildingLibcxx.html for building the runtimes.")
+    message(FATAL_ERROR
+      "Using LLVM_ENABLE_PROJECTS=${proj} is incorrect. Please use -DLLVM_ENABLE_RUNTIMES=${proj} or "
+      "see the instructions at https://libcxx.llvm.org/BuildingLibcxx.html for building the runtimes.")
   endif()
 endforeach()