Breaking change: prohibit using Bazel+MSVC to build protobuf

An opt-out flag `--define=protobuf_allow_msvc=true` will be available until our 2026 breaking release 34.0. See #20085 for more details.

#test-continuous

PiperOrigin-RevId: 718525948

.github/workflows/test_cpp.yml

@@ -414,9 +414,17 @@ jobs:
             # Current github runners are all Intel based, so just build/compile
             # for Apple Silicon to detect issues there.
             bazel: build --cpu=darwin_arm64 //src/... //third_party/utf8_range/... //conformance:conformance_framework_tests
-          - name: Windows Bazel
+          - name: Windows Bazel (failing)
             os: windows-2022
             cache_key: windows-2022-bazel7
+            bazel: test //src/...  @com_google_protobuf_examples//... --config=msvc-cl --test_tag_filters=-conformance --build_tag_filters=-conformance
+          - name: Windows Bazel
+            os: windows-2022
+            cache_key: windows-2022-msvc-cl
+            bazel: test //src/...  @com_google_protobuf_examples//... --config=msvc-cl --test_tag_filters=-conformance --build_tag_filters=-conformance --define=protobuf_allow_msvc=true
+          - name: Windows Bazel clang-cl
+            os: windows-2022
+            cache_key: windows-2022-clang-cl
             bazel: test //src/...  @com_google_protobuf_examples//... --test_tag_filters=-conformance --build_tag_filters=-conformance
     name: ${{ matrix.continuous-only && inputs.continuous-prefix || '' }} ${{ matrix.name }}
     runs-on: ${{ matrix.os }}
@@ -528,6 +536,7 @@ jobs:
         if: ${{ matrix.install-flags && (!matrix.continuous-only || inputs.continuous-run) }}
         uses: protocolbuffers/protobuf-ci/bash@v4
         with:
+          bazel-version: 7.1.2
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
           command: >-
             cmake . -DCMAKE_CXX_STANDARD=17 ${{ matrix.install-flags }}
@@ -554,6 +563,7 @@ jobs:
         uses: protocolbuffers/protobuf-ci/bash@v4
         with:
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
+          bazel-version: 7.1.2
           command: >-
             cmake . -DCMAKE_CXX_STANDARD=17 ${{ matrix.flags }}
             ${{ env.SCCACHE_CMAKE_FLAGS }} -Dprotobuf_ALLOW_CCACHE=ON

.github/workflows/test_csharp.yml

@@ -74,6 +74,7 @@ jobs:
       - name: Run tests
         uses: protocolbuffers/protobuf-ci/bash@v4
         with:
+          bazel-version: 7.1.2
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
           command: |
             dotnet build csharp/src/Google.Protobuf.sln

build_defs/BUILD.bazel

@@ -18,12 +18,27 @@ create_compiler_config_setting(
     value = "msvc-cl",
 )
 
-# Caveat: clang-cl support in protobuf is only best-effort / untested for now.
 create_compiler_config_setting(
     name = "config_clang_cl",
     value = "clang-cl",
 )
 
+platform(
+    name = "x64_windows-clang-cl",
+    constraint_values = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:windows",
+        "@bazel_tools//tools/cpp:clang-cl",
+    ],
+)
+
+config_setting(
+    name = "protobuf_allow_msvc",
+    values = {
+        "define": "protobuf_allow_msvc=true",
+    },
+)
+
 selects.config_setting_group(
     name = "config_msvc",
     match_any = [

ci/Windows.bazelrc

@@ -5,3 +5,6 @@ build --cxxopt=/std:c++17 --host_cxxopt=/std:c++17
 startup --output_user_root=C:/tmp --windows_enable_symlinks
 common --enable_runfiles
 
+build:clang-cl --extra_toolchains=@local_config_cc//:cc-toolchain-x64_windows-clang-cl --extra_execution_platforms=//build_defs:x64_windows-clang-cl --host_platform=//build_defs:x64_windows-clang-cl
+build:msvc-cl --extra_toolchains= --extra_execution_platforms=
+build --config=clang-cl

examples/.bazelrc

@@ -3,6 +3,7 @@ common --enable_platform_specific_config
 build:linux --cxxopt=-std=c++17 --host_cxxopt=-std=c++17
 build:macos --cxxopt=-std=c++17 --host_cxxopt=-std=c++17
 
+build:windows --extra_toolchains=@local_config_cc//:cc-toolchain-x64_windows-clang-cl --extra_execution_platforms=//:x64_windows-clang-cl
 common:windows --cxxopt=/std:c++17 --host_cxxopt=/std:c++17 --enable_runfiles
 
 build --experimental_remote_cache_eviction_retries=5

examples/BUILD.bazel

@@ -185,3 +185,12 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//visibility:public"],
 )
+
+platform(
+    name = "x64_windows-clang-cl",
+    constraint_values = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:windows",
+        "@bazel_tools//tools/cpp:clang-cl",
+    ],
+)

src/google/protobuf/stubs/BUILD.bazel

@@ -22,6 +22,12 @@ cc_library(
         "status_macros.h",
     ],
     copts = COPTS,
+    defines = ["GOOGLE_PROTOBUF_USING_BAZEL=1"] + select({
+        "//build_defs:protobuf_allow_msvc": [
+            "GOOGLE_PROTOBUF_MSVC_BAZEL_OVERRIDE=1",
+        ],
+        "//conditions:default": [],
+    }),
     linkopts = LINK_OPTS,
     strip_include_prefix = "/src",
     deps = [

src/google/protobuf/stubs/port.h

@@ -31,6 +31,13 @@
 #include <byteswap.h>  // IWYU pragma: export
 #endif
 
+#if defined(_MSC_VER) && !defined(__clang__) && \
+    defined(GOOGLE_PROTOBUF_USING_BAZEL) &&     \
+    !defined(GOOGLE_PROTOBUF_MSVC_BAZEL_OVERRIDE)
+#error \
+    "Protobuf will be dropping support for MSVC + Bazel in 34.0.  To continue using it until then, use the flag --define=protobuf_allow_msvc=true.  See github.com/protocolbuffers/protobuf/issues/20085 for more information."
+#endif
+
 // Legacy: some users reference these (internal-only) macros even though we
 // don't need them any more.
 #if defined(_MSC_VER) && defined(PROTOBUF_USE_DLLS)