[build] Support clang-cl for Windows builds (best effort) (#36831)

Usage: `bazel build --config=clang-cl --build_tag_filters=-no_windows :all`

The highlight, for me anyway: thread safety annotation checking can now be done on Windows-only code.

clang-cl's interpretation of `-Wall` differs from that of clang on linux. This PR uses the set of warnings enabled on linux, and whittles down the list until all builds pass. I left comments in `copts.bzl` describing the warnings, many of which can be removed with targeted code cleanups.

Closes #36831

PiperOrigin-RevId: 641009783

BUILD

@@ -19,6 +19,7 @@ load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
 load(
     "//bazel:grpc_build_system.bzl",
     "grpc_cc_library",
+    "grpc_clang_cl_settings",
     "grpc_filegroup",
     "grpc_generate_one_off_targets",
     "grpc_upb_proto_library",
@@ -66,6 +67,8 @@ bool_flag(
     build_setting_default = False,
 )
 
+grpc_clang_cl_settings()
+
 config_setting(
     name = "grpc_no_rls_flag",
     flag_values = {":disable_grpc_rls": "true"},
@@ -216,6 +219,11 @@ config_setting(
     values = {"define": "use_strict_warning=true"},
 )
 
+config_setting(
+    name = "use_strict_warning_windows",
+    values = {"define": "use_strict_warning_windows=true"},
+)
+
 python_config_settings()
 
 # This should be updated along with build_handwritten.yaml

bazel/copts.bzl

@@ -57,7 +57,104 @@ GRPC_LLVM_WARNING_FLAGS = [
     "-Wno-unused-function",
 ]
 
+GRPC_LLVM_WINDOWS_WARNING_FLAGS = GRPC_LLVM_WARNING_FLAGS + [
+    ### Some checks that are missing with clang-cl
+    "-Wthread-safety",
+    "-Wreorder-ctor",
+
+    ### Avoid some checks that are default on clang-cl
+    "-Wno-c++98-compat-pedantic",
+    "-Wno-missing-prototypes",
+    "-Wno-thread-safety-precise",  # too many aliases
+
+    # abseil offenses
+    "-Wno-comma",
+    "-Wno-deprecated-redundant-constexpr-static-def",
+    "-Wno-deprecated",  # remove when the above works in all clang versions we test with
+    "-Wno-float-equal",
+    "-Wno-gcc-compat",
+    "-Wno-reserved-identifier",
+    "-Wno-thread-safety-negative",
+    "-Wno-sign-compare",
+
+    # re2 offenses
+    "-Wno-zero-as-null-pointer-constant",
+
+    # ares offenses
+    "-Wno-macro-redefined",
+
+    # protobuf offenses
+    "-Wno-cast-align",
+    "-Wno-inconsistent-missing-destructor-override",
+
+    # xxhash offenses
+    "-Wno-disabled-macro-expansion",
+
+    # benchmark offenses
+    "-Wno-shift-sign-overflow",
+
+    # Evidently nodiscard is inappropriately pinned as a C++17 feature
+    "-Wno-c++17-attribute-extensions",
+
+    # declarations are not used in many places
+    "-Wno-missing-variable-declarations",
+
+    # TODO: delete iomgr
+    "-Wno-old-style-cast",
+    "-Wno-cast-qual",
+    "-Wno-unused-member-function",
+    "-Wno-unused-template",
+
+    # TODO(hork): see if the TraceFlag offense can be removed
+    "-Wno-global-constructors",
+    # TODO(hork): clean up EE offenses
+    "-Wno-missing-field-initializers",
+    "-Wno-non-virtual-dtor",
+
+    # TODO(ctiller): offense: dump_args. signed to unsigned
+    "-Wno-sign-conversion",
+    "-Wno-shorten-64-to-32",
+
+    # TODO: general cleanup required. Maybe new developer or rainy day projects.
+    "-Wno-unreachable-code-break",
+    "-Wno-unreachable-code-return",
+    "-Wno-unreachable-code",
+    "-Wno-used-but-marked-unused",
+    "-Wno-newline-eof",
+    "-Wno-unused-const-variable",
+    "-Wno-extra-semi",
+    "-Wno-extra-semi-stmt",
+    "-Wno-suggest-destructor-override",
+    "-Wno-shadow",
+    "-Wno-missing-noreturn",
+    "-Wno-nested-anon-types",
+    "-Wno-gnu-anonymous-struct",
+    "-Wno-nonportable-system-include-path",
+    "-Wno-microsoft-cast",
+    "-Wno-exit-time-destructors",
+    "-Wno-undef",  # #if <MACRO_NAME> to #ifdef <MACRO_NAME>
+    "-Wno-unused-macros",
+    "-Wno-redundant-parens",
+    "-Wno-undefined-func-template",
+    "-Wno-gnu-zero-variadic-macro-arguments",
+    "-Wno-double-promotion",
+    "-Wno-implicit-float-conversion",
+    "-Wno-implicit-int-conversion",
+    "-Wno-float-conversion",
+    "-Wno-unused-parameter",
+    "-Wno-suggest-override",
+    "-Wno-documentation",
+    "-Wno-documentation-unknown-command",
+
+    ### possibly bad warnings for this codebase
+    "-Wno-covered-switch-default",
+    "-Wno-switch-enum",
+    "-Wno-c99-extensions",
+    "-Wno-unused-private-field",  # GRPC_UNUSED does not appear to work for private fields
+]
+
 GRPC_DEFAULT_COPTS = select({
     "//:use_strict_warning": GRPC_LLVM_WARNING_FLAGS + ["-DUSE_STRICT_WARNING=1"],
+    "//:use_strict_warning_windows": GRPC_LLVM_WINDOWS_WARNING_FLAGS + ["-DUSE_STRICT_WARNING=1"],
     "//conditions:default": [],
 })

bazel/grpc_build_system.bzl

@@ -45,6 +45,7 @@ def if_not_windows(a):
     return select({
         "//:windows": [],
         "//:windows_msvc": [],
+        "//:windows_clang": [],
         "//conditions:default": a,
     })
 
@@ -52,6 +53,7 @@ def if_windows(a):
     return select({
         "//:windows": a,
         "//:windows_msvc": a,
+        "//:windows_clang": a,
         "//conditions:default": [],
     })
 
@@ -802,3 +804,22 @@ def python_config_settings():
         name = "python3",
         flag_values = {"@bazel_tools//tools/python:python_version": "PY3"},
     )
+
+# buildifier: disable=unnamed-macro
+def grpc_clang_cl_settings():
+    native.platform(
+        name = "x64_windows-clang-cl",
+        constraint_values = [
+            "@platforms//cpu:x86_64",
+            "@platforms//os:windows",
+            "@bazel_tools//tools/cpp:clang-cl",
+        ],
+    )
+    native.config_setting(
+        name = "windows_clang",
+        constraint_values = [
+            "@platforms//cpu:x86_64",
+            "@platforms//os:windows",
+            "@bazel_tools//tools/cpp:clang-cl",
+        ],
+    )

bazel/grpc_deps.bzl

@@ -222,6 +222,7 @@ def grpc_deps():
             ],
             patches = [
                 "@com_github_grpc_grpc//third_party:protobuf.patch",
+                "@com_github_grpc_grpc//third_party:protobuf.10007.patch",
             ],
             patch_args = ["-p1"],
         )

src/core/BUILD

@@ -2733,6 +2733,7 @@ grpc_cc_library(
         {
             "//:windows": ["windows_event_engine"],
             "//:windows_msvc": ["windows_event_engine"],
+            "//:windows_clang": ["windows_event_engine"],
             "//:windows_other": ["windows_event_engine"],
             "//:mac": [
                 "posix_event_engine",

third_party/protobuf.10007.patch

@@ -0,0 +1,30 @@
+diff --git a/build_defs/BUILD.bazel b/build_defs/BUILD.bazel
+index 1c72eba68..176ab5a91 100644
+--- a/build_defs/BUILD.bazel
++++ b/build_defs/BUILD.bazel
+@@ -14,10 +14,24 @@ package(
+ )
+ 
+ create_compiler_config_setting(
+-    name = "config_msvc",
++    name = "config_msvc_cl",
+     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",
++)
++
++selects.config_setting_group(
++    name = "config_msvc",
++    match_any = [
++        ":config_clang_cl",
++        ":config_msvc_cl",
++    ],
++)
++
+ config_setting(
+     name = "aarch64",
+     values = {"cpu": "linux-aarch_64"},

tools/bazel.rc

@@ -44,6 +44,12 @@ build:macos --dynamic_mode=off
 build:windows_opt --compilation_mode=opt
 build:windows_dbg --compilation_mode=dbg
 
+build:clang-cl --extra_toolchains=@local_config_cc//:cc-toolchain-x64_windows-clang-cl
+build:clang-cl --extra_execution_platforms=//:x64_windows-clang-cl
+build:clang-cl --incompatible_enable_cc_toolchain_resolution
+build:clang-cl --define=use_strict_warning_windows=true
+build:clang-cl --compiler=clang-cl
+
 build:asan --strip=never
 build:asan --copt=-fsanitize=address
 build:asan --copt=-O0