ngcpp · mingxwa · Jun 20, 2026 · Jun 20, 2026
diff --git a/.bazelrc b/.bazelrc
@@ -5,6 +5,10 @@ common --enable_platform_specific_config
 # Default Build Options
 build --features=external_include_paths
 
+# Freestanding Configuration
+build:freestanding --cxxopt=-ffreestanding --cxxopt=-fno-exceptions --cxxopt=-fno-rtti
+build:freestanding --linkopt=-nodefaultlibs --linkopt=-lc
+
 # Platform-Specific Toolchain Overrides
 build:linux --repo_env=BAZEL_CXXOPTS=-std=c++20
 build:macos --repo_env=BAZEL_CXXOPTS=-std=c++20

diff --git a/.github/workflows/bvt-appleclang.yml b/.github/workflows/bvt-appleclang.yml
@@ -22,26 +22,37 @@ jobs:
 
     - name: Build and run test with AppleClang on cmake
       run: |
-        cmake -B build-cmake -GNinja -DCMAKE_CXX_STANDARD=23 -DCMAKE_BUILD_TYPE=Release -DPROXY_BUILD_MODULES=FALSE
-        cmake --build build-cmake -j
-        ctest --test-dir build-cmake -j
-        mkdir build-cmake/drop
-        bash ./tools/dump_build_env.sh c++ build-cmake/drop/env-info.json
+        cmake --preset default -DCMAKE_CXX_STANDARD=23 -DPROXY_BUILD_MODULES=FALSE
+        cmake --build --preset default -j
+        ctest --preset default -j
+        mkdir build/cmake/drop
+        bash ./tools/dump_build_env.sh c++ build/cmake/drop/env-info.json
+
+    - name: Build and run freestanding test with AppleClang on cmake
+      run: |
+        cmake --preset freestanding -DCMAKE_CXX_STANDARD=23 -DPROXY_BUILD_MODULES=FALSE
+        cmake --build --preset freestanding -j
+        ctest --preset freestanding -j
 
     - name: Build and run test with AppleClang on meson
       run: |
-        meson setup build-meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled
-        meson test -C build-meson
-        meson test -C build-meson --benchmark --test-args=--benchmark_list_tests=true
+        meson setup build/meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled
+        meson test -C build/meson
+        meson test -C build/meson --benchmark --test-args=--benchmark_list_tests=true
+
+    - name: Build and run freestanding test with AppleClang on meson
+      run: |
+        meson setup build/meson-freestanding --buildtype=release -Dfreestanding=true
+        meson test -C build/meson-freestanding
 
     - name: Build and Run test with AppleClang on bazel
       run: bazel test --lockfile_mode=error //tests:proxy_tests //benchmarks:proxy_benchmarks //docs/...
 
     - name: Run benchmarks
-      run: build-cmake/benchmarks/msft_proxy_benchmarks --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build-cmake/drop/benchmarking-results.json
+      run: build/cmake/benchmarks/msft_proxy_benchmarks --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build/cmake/drop/benchmarking-results.json
 
     - name: Archive benchmarking results
       uses: actions/upload-artifact@v7
       with:
         name: drop-appleclang
-        path: build-cmake/drop/
+        path: build/cmake/drop/
diff --git a/.github/workflows/bvt-clang.yml b/.github/workflows/bvt-clang.yml
@@ -34,26 +34,40 @@ jobs:
 
     - name: Build and run test with clang ${{ env.CLANG_VERSION }} on cmake
       run: |
-        cmake -B build-cmake -GNinja -DCMAKE_CXX_STANDARD=23 -DCMAKE_BUILD_TYPE=Release -DPROXY_BUILD_MODULES=TRUE
-        cmake --build build-cmake -j
-        ctest --test-dir build-cmake -j
-        mkdir build-cmake/drop
-        bash ./tools/dump_build_env.sh "$CXX" build-cmake/drop/env-info.json
+        cmake --preset default -DCMAKE_CXX_STANDARD=23 -DPROXY_BUILD_MODULES=TRUE
+        cmake --build --preset default -j
+        ctest --preset default -j
+        mkdir build/cmake/drop
+        bash ./tools/dump_build_env.sh "$CXX" build/cmake/drop/env-info.json
+
+    - name: Build and run freestanding test with clang ${{ env.CLANG_VERSION }} on cmake
+      run: |
+        cmake --preset freestanding -DCMAKE_CXX_STANDARD=23 -DPROXY_BUILD_MODULES=TRUE
+        cmake --build --preset freestanding -j
+        ctest --preset freestanding -j
 
     - name: Build and run test with clang ${{ env.CLANG_VERSION }} on meson
       run: |
-        meson setup build-meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled
-        meson test -C build-meson
-        meson test -C build-meson --benchmark --test-args=--benchmark_list_tests=true
+        meson setup build/meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled
+        meson test -C build/meson
+        meson test -C build/meson --benchmark --test-args=--benchmark_list_tests=true
+
+    - name: Build and run freestanding test with clang ${{ env.CLANG_VERSION }} on meson
+      run: |
+        meson setup build/meson-freestanding --buildtype=release -Dfreestanding=true
+        meson test -C build/meson-freestanding
 
     - name: Build and Run test with clang ${{ env.CLANG_VERSION }} on bazel
-      run: bazel test --lockfile_mode=error //tests:proxy_tests //tests:proxy_freestanding_tests //benchmarks:proxy_benchmarks //docs/...
+      run: bazel test --lockfile_mode=error //tests:proxy_tests //benchmarks:proxy_benchmarks //docs/...
+
+    - name: Build and run freestanding test with clang ${{ env.CLANG_VERSION }} on bazel
+      run: bazel test --config=freestanding --lockfile_mode=error //tests:proxy_freestanding_tests
 
     - name: Run benchmarks
-      run: build-cmake/benchmarks/msft_proxy_benchmarks --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build-cmake/drop/benchmarking-results.json
+      run: build/cmake/benchmarks/msft_proxy_benchmarks --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build/cmake/drop/benchmarking-results.json
 
     - name: Archive benchmarking results
       uses: actions/upload-artifact@v7
       with:
         name: drop-clang
-        path: build-cmake/drop/
+        path: build/cmake/drop/
diff --git a/.github/workflows/bvt-compatibility.yml b/.github/workflows/bvt-compatibility.yml
@@ -11,7 +11,7 @@ jobs:
       matrix:
         compiler:
           - {family: gcc, version: 13, modules: false, doc_tests: true}
-          - {family: gcc, version: 14, modules: true, doc_tests: true}
+          - {family: gcc, version: 14, modules: false, doc_tests: true}
           - {family: clang, version: 16, modules: false, doc_tests: false}
           - {family: clang, version: 17, modules: false, doc_tests: true}
           - {family: clang, version: 18, modules: false, doc_tests: true}
@@ -53,6 +53,12 @@ jobs:
 
     - name: Build and run test with cmake
       run: |
-        cmake -B build -GNinja -DCMAKE_BUILD_TYPE=Release '-DPROXY_BUILD_MODULES=${{ matrix.compiler.modules }}' '-DBUILD_DOC_TESTING=${{ matrix.compiler.doc_tests }}'
-        cmake --build build -j
-        ctest --test-dir build -j
+        cmake --preset default '-DPROXY_BUILD_MODULES=${{ matrix.compiler.modules }}' '-DBUILD_DOC_TESTING=${{ matrix.compiler.doc_tests }}'
+        cmake --build --preset default -j
+        ctest --preset default -j
+
+    - name: Build and run freestanding test with cmake
+      run: |
+        cmake --preset freestanding '-DPROXY_BUILD_MODULES=${{ matrix.compiler.modules }}' '-DBUILD_DOC_TESTING=${{ matrix.compiler.doc_tests }}'
+        cmake --build --preset freestanding -j
+        ctest --preset freestanding -j
diff --git a/.github/workflows/bvt-gcc.yml b/.github/workflows/bvt-gcc.yml
@@ -27,27 +27,41 @@ jobs:
 
     - name: Build and run test with gcc 15 on cmake
       run: |
-        cmake -B build-cmake -GNinja -DCMAKE_CXX_STANDARD=23 -DCMAKE_BUILD_TYPE=Release -DPROXY_BUILD_MODULES=TRUE
-        cmake --build build-cmake -j
-        ctest --test-dir build-cmake -j
-        mkdir build-cmake/drop
+        cmake --preset default -DCMAKE_CXX_STANDARD=23 -DPROXY_BUILD_MODULES=TRUE
+        cmake --build --preset default -j
+        ctest --preset default -j
+        mkdir build/cmake/drop
         chmod +x tools/dump_build_env.sh
-        ./tools/dump_build_env.sh g++ build-cmake/drop/env-info.json
+        ./tools/dump_build_env.sh g++ build/cmake/drop/env-info.json
+
+    - name: Build and run freestanding test with gcc 15 on cmake
+      run: |
+        cmake --preset freestanding -DCMAKE_CXX_STANDARD=23 -DPROXY_BUILD_MODULES=TRUE
+        cmake --build --preset freestanding -j
+        ctest --preset freestanding -j
 
     - name: Build and run test with gcc 15 on meson
       run: |
-        meson setup build-meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled
-        meson test -C build-meson
-        meson test -C build-meson --benchmark --test-args=--benchmark_list_tests=true
+        meson setup build/meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled
+        meson test -C build/meson
+        meson test -C build/meson --benchmark --test-args=--benchmark_list_tests=true
+
+    - name: Build and run freestanding test with gcc 15 on meson
+      run: |
+        meson setup build/meson-freestanding --buildtype=release -Dfreestanding=true
+        meson test -C build/meson-freestanding
 
     - name: Build and Run test with gcc 15 on bazel
-      run: bazel test --lockfile_mode=error //tests:proxy_tests //tests:proxy_freestanding_tests //benchmarks:proxy_benchmarks //docs/...
+      run: bazel test --lockfile_mode=error //tests:proxy_tests //benchmarks:proxy_benchmarks //docs/...
+
+    - name: Build and run freestanding test with gcc 15 on bazel
+      run: bazel test --config=freestanding --lockfile_mode=error //tests:proxy_freestanding_tests
 
     - name: Run benchmarks
-      run: build-cmake/benchmarks/msft_proxy_benchmarks --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build-cmake/drop/benchmarking-results.json
+      run: build/cmake/benchmarks/msft_proxy_benchmarks --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build/cmake/drop/benchmarking-results.json
 
     - name: Archive benchmarking results
       uses: actions/upload-artifact@v7
       with:
         name: drop-gcc
-        path: build-cmake/drop/
+        path: build/cmake/drop/
diff --git a/.github/workflows/bvt-msvc.yml b/.github/workflows/bvt-msvc.yml
@@ -22,26 +22,26 @@ jobs:
 
     - name: Build and run test with MSVC on cmake
       run: |
-        cmake -B build-cmake -DCMAKE_CXX_STANDARD=23 -DPROXY_BUILD_MODULES=TRUE `
-          && cmake --build build-cmake --config Release -j `
-          && ctest --test-dir build-cmake -C Release -j `
-          && mkdir build-cmake\drop > $null `
-          && .\tools\dump_build_env_msvc.ps1 -OutputPath build-cmake\drop\env-info.json
+        cmake -B build/cmake -DCMAKE_CXX_STANDARD=23 -DPROXY_BUILD_MODULES=TRUE `
+          && cmake --build build/cmake --config Release -j `
+          && ctest --test-dir build/cmake -C Release -j `
+          && mkdir build/cmake/drop > $null `
+          && .\tools\dump_build_env_msvc.ps1 -OutputPath build/cmake/drop/env-info.json
 
     - name: Build and run test with MSVC on meson
       run: |
-        meson setup build-meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled --vsenv
-        meson test -C build-meson
-        meson test -C build-meson --benchmark --test-args=--benchmark_list_tests=true
+        meson setup build/meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled --vsenv
+        meson test -C build/meson
+        meson test -C build/meson --benchmark --test-args=--benchmark_list_tests=true
 
     - name: Build and Run test with MSVC on bazel
       run: bazel test --lockfile_mode=error //tests:proxy_tests //benchmarks:proxy_benchmarks //docs/...
 
     - name: Run benchmarks
-      run: build-cmake\benchmarks\Release\msft_proxy_benchmarks.exe --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build-cmake\drop\benchmarking-results.json
+      run: build/cmake/benchmarks/Release/msft_proxy_benchmarks.exe --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build/cmake/drop/benchmarking-results.json
 
     - name: Archive benchmarking results
       uses: actions/upload-artifact@v7
       with:
         name: drop-msvc
-        path: build-cmake/drop/
+        path: build/cmake/drop/
diff --git a/.github/workflows/bvt-nvhpc.yml b/.github/workflows/bvt-nvhpc.yml
@@ -37,24 +37,24 @@ jobs:
 
     - name: Build and run test with NVHPC ${{ env.NVHPC_VERSION }} on cmake
       run: |
-        cmake -B build-cmake -GNinja -DCMAKE_BUILD_TYPE=Release -DPROXY_BUILD_MODULES=FALSE
-        cmake --build build-cmake -j
-        ctest --test-dir build-cmake -j
-        mkdir build-cmake/drop
+        cmake --preset default -DPROXY_BUILD_MODULES=FALSE
+        cmake --build --preset default -j
+        ctest --preset default -j
+        mkdir build/cmake/drop
         chmod +x tools/dump_build_env.sh
-        ./tools/dump_build_env.sh "$CXX" build-cmake/drop/env-info.json
+        ./tools/dump_build_env.sh "$CXX" build/cmake/drop/env-info.json
 
     - name: Build and run test with NVHPC ${{ env.NVHPC_VERSION }} on meson
       run: |
-        meson setup build-meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled
-        meson test -C build-meson
-        meson test -C build-meson --benchmark --test-args=--benchmark_list_tests=true
+        meson setup build/meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled
+        meson test -C build/meson
+        meson test -C build/meson --benchmark --test-args=--benchmark_list_tests=true
 
     - name: Run benchmarks
-      run: build-cmake/benchmarks/msft_proxy_benchmarks --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build-cmake/drop/benchmarking-results.json
+      run: build/cmake/benchmarks/msft_proxy_benchmarks --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build/cmake/drop/benchmarking-results.json
 
     - name: Archive benchmarking results
       uses: actions/upload-artifact@v7
       with:
         name: drop-nvhpc
-        path: build-cmake/drop/
+        path: build/cmake/drop/
diff --git a/.github/workflows/bvt-oneapi.yml b/.github/workflows/bvt-oneapi.yml
@@ -42,26 +42,40 @@ jobs:
 
     - name: Build and run test with oneapi on cmake
       run: |
-        cmake -B build-cmake -GNinja -DCMAKE_CXX_STANDARD=23 -DCMAKE_BUILD_TYPE=Release
-        cmake --build build-cmake -j
-        ctest --test-dir build-cmake -j
-        mkdir build-cmake/drop
-        bash ./tools/dump_build_env.sh "$CXX" build-cmake/drop/env-info.json
+        cmake --preset default -DCMAKE_CXX_STANDARD=23
+        cmake --build --preset default -j
+        ctest --preset default -j
+        mkdir build/cmake/drop
+        bash ./tools/dump_build_env.sh "$CXX" build/cmake/drop/env-info.json
+
+    - name: Build and run freestanding test with oneapi on cmake
+      run: |
+        cmake --preset freestanding -DCMAKE_CXX_STANDARD=23
+        cmake --build --preset freestanding -j
+        ctest --preset freestanding -j
 
     - name: Build and run test with oneapi on meson
       run: |
-        meson setup build-meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled
-        meson test -C build-meson
-        meson test -C build-meson --benchmark --test-args=--benchmark_list_tests=true
+        meson setup build/meson --buildtype=release -Dtests=enabled -Dbenchmarks=enabled
+        meson test -C build/meson
+        meson test -C build/meson --benchmark --test-args=--benchmark_list_tests=true
+
+    - name: Build and run freestanding test with oneapi on meson
+      run: |
+        meson setup build/meson-freestanding --buildtype=release -Dfreestanding=true
+        meson test -C build/meson-freestanding
 
     - name: Build and Run test with oneapi on bazel
-      run: bazel test --lockfile_mode=error --cxxopt=-Wno-c++23-extensions --test_env=LD_LIBRARY_PATH //tests:proxy_tests //tests:proxy_freestanding_tests //benchmarks:proxy_benchmarks //docs/...
+      run: bazel test --lockfile_mode=error --cxxopt=-Wno-c++23-extensions --test_env=LD_LIBRARY_PATH //tests:proxy_tests //benchmarks:proxy_benchmarks //docs/...
+
+    - name: Build and run freestanding test with oneapi on bazel
+      run: bazel test --config=freestanding --lockfile_mode=error --cxxopt=-Wno-c++23-extensions --test_env=LD_LIBRARY_PATH //tests:proxy_freestanding_tests
 
     - name: Run benchmarks
-      run: build-cmake/benchmarks/msft_proxy_benchmarks --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build-cmake/drop/benchmarking-results.json
+      run: build/cmake/benchmarks/msft_proxy_benchmarks --benchmark_min_warmup_time=0.1 --benchmark_min_time=0.1s --benchmark_repetitions=30 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true --benchmark_format=json > build/cmake/drop/benchmarking-results.json
 
     - name: Archive benchmarking results
       uses: actions/upload-artifact@v7
       with:
         name: drop-oneapi
-        path: build-cmake/drop/
+        path: build/cmake/drop/
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -22,6 +22,16 @@ if(PROJECT_IS_TOP_LEVEL)
     "When this project is top level, build the docs and tests with C++ module support."
     OFF
   )
+  option(
+    PROXY_FREESTANDING
+    "When this project is top level, configure proxy and its tests for a freestanding environment. GCC/Clang only."
+    OFF
+  )
+endif()
+
+if(PROXY_FREESTANDING)
+  add_compile_options(-ffreestanding -fno-exceptions -fno-rtti)
+  add_link_options(-nodefaultlibs -lc)
 endif()
 
 file(GLOB_RECURSE proxy_public_headers CONFIGURE_DEPENDS
@@ -101,24 +111,6 @@ install(
 if(BUILD_TESTING)
   include(CTest)
 
-  include(cmake/read_dependencies.cmake)
-  proxy_read_dependencies("${CMAKE_CURRENT_SOURCE_DIR}/cmake/dependencies.json")
-
-  include(FetchContent)
-  # The policy uses the download time for timestamp, instead of the timestamp in the archive. This
-  # allows for proper rebuilds when a projects URL changes.
-  if(POLICY CMP0135)
-    cmake_policy(SET CMP0135 NEW)
-  endif()
-
-  FetchContent_Declare(
-    fmt
-    URL ${PROXY_FMT_URL}
-    URL_HASH SHA256=${PROXY_FMT_SHA256}
-    SYSTEM
-  )
-  FetchContent_MakeAvailable(fmt)
-
   if(MSVC)
     set(PROXY_BUILD_FLAGS /utf-8 /W4)
     set(PROXY_STRICT_WARNING_FLAGS ${PROXY_BUILD_FLAGS} /WX)
@@ -133,10 +125,32 @@ if(BUILD_TESTING)
     set(PROXY_STRICT_WARNING_FLAGS ${PROXY_BUILD_FLAGS} -Werror)
   endif()
 
-  add_subdirectory(tests)
-  add_subdirectory(benchmarks)
+  if(PROXY_FREESTANDING)
+    add_subdirectory(tests/freestanding)
+  else()
+    include(cmake/read_dependencies.cmake)
+    proxy_read_dependencies("${CMAKE_CURRENT_SOURCE_DIR}/cmake/dependencies.json")
+
+    include(FetchContent)
+    # The policy uses the download time for timestamp, instead of the timestamp in the archive. This
+    # allows for proper rebuilds when a projects URL changes.
+    if(POLICY CMP0135)
+      cmake_policy(SET CMP0135 NEW)
+    endif()
+
+    FetchContent_Declare(
+      fmt
+      URL ${PROXY_FMT_URL}
+      URL_HASH SHA256=${PROXY_FMT_SHA256}
+      SYSTEM
+    )
+    FetchContent_MakeAvailable(fmt)
+
+    add_subdirectory(tests)
+    add_subdirectory(benchmarks)
 
-  if(BUILD_DOC_TESTING)
-    add_subdirectory(docs)
+    if(BUILD_DOC_TESTING)
+      add_subdirectory(docs)
+    endif()
   endif()
 endif()