build: add experimental support for Zig C/C++ compiler.

.bazelrc

@@ -8,6 +8,18 @@ build:clang --action_env=BAZEL_COMPILER=clang
 build:clang --action_env=CC=clang
 build:clang --action_env=CXX=clang++
 
+# Use Zig C/C++ compiler.
+build:zig-cc --incompatible_enable_cc_toolchain_resolution
+build:zig-cc --extra_toolchains @zig_sdk//:aarch64-linux-gnu.2.28_toolchain
+build:zig-cc --extra_toolchains @zig_sdk//:x86_64-linux-gnu.2.28_toolchain
+build:zig-cc --host_copt=-fno-sanitize=undefined
+
+# Use Zig C/C++ compiler (cross-compile to Linux/aarch64).
+build:zig-cc-linux-aarch64 --config=zig-cc
+build:zig-cc-linux-aarch64 --platforms @zig_sdk//:linux_aarch64_platform
+build:zig-cc-linux-aarch64 --run_under=qemu-aarch64-static
+build:zig-cc-linux-aarch64 --test_env=QEMU_LD_PREFIX=/usr/aarch64-linux-gnu/
+
 build --enable_platform_specific_config
 
 build:linux --cxxopt=-std=c++17

.github/workflows/cpp.yml

@@ -121,6 +121,13 @@ jobs:
           arch: x86_64
           action: test
           flags: --config=clang --define=crypto=system
+        - name: 'V8 on Linux/aarch64'
+          runtime: 'v8'
+          repo: 'v8'
+          os: ubuntu-20.04
+          arch: aarch64
+          action: test
+          flags: --config=zig-cc-linux-aarch64 --@v8//bazel/config:v8_target_cpu=arm64
         - name: 'V8 on macOS/x86_64'
           runtime: 'v8'
           repo: 'v8'
@@ -181,7 +188,7 @@ jobs:
     - uses: actions/checkout@v2
 
     - name: Activate Docker/QEMU
-      if: startsWith(matrix.run_under, 'docker')
+      if: ${{ matrix.arch != 'x86_64' }}
       run: docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
 
     - name: Set cache key

bazel/dependencies.bzl

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+load("@bazel-zig-cc//toolchain:defs.bzl", zig_register_toolchains = "register_toolchains")
 load("@com_google_protobuf//:protobuf_deps.bzl", "protobuf_deps")
 load("@proxy_wasm_cpp_host//bazel/cargo/wasmsign:crates.bzl", "wasmsign_fetch_remote_crates")
 load("@proxy_wasm_cpp_host//bazel/cargo/wasmtime:crates.bzl", "wasmtime_fetch_remote_crates")
@@ -32,6 +33,8 @@ def proxy_wasm_cpp_host_dependencies():
         version = "1.58.1",
     )
 
+    zig_register_toolchains()
+
     # Core dependencies.
 
     protobuf_deps()

bazel/external/v8.patch

@@ -1,4 +1,5 @@
-# Disable pointer compression (limits the maximum number of WasmVMs).
+# 1. Disable pointer compression (limits the maximum number of WasmVMs).
+# 2. Don't override v8_target_cpu (https://crrev.com/c/3445204).
 
 diff --git a/BUILD.bazel b/BUILD.bazel
 index 1cc0121e60..4947c1dba2 100644
@@ -13,3 +14,29 @@ index 1cc0121e60..4947c1dba2 100644
  )
 
  # Default setting for v8_enable_pointer_compression.
+diff --git a/bazel/defs.bzl b/bazel/defs.bzl
+index fe27db305b..dee5e69cc4 100644
+--- a/bazel/defs.bzl
++++ b/bazel/defs.bzl
+@@ -372,6 +372,12 @@ def v8_torque(name, noicu_srcs, icu_srcs, args, extras):
+     )
+
+ def _v8_target_cpu_transition_impl(settings, attr):
++    # Check for an existing v8_target_cpu flag.
++    if "@v8//bazel/config:v8_target_cpu" in settings:
++        if settings["@v8//bazel/config:v8_target_cpu"] != "none":
++            return
++
++    # Auto-detect target architecture based on the --cpu flag.
+     mapping = {
+         "haswell": "x64",
+         "k8": "x64",
+@@ -395,7 +401,7 @@ def _v8_target_cpu_transition_impl(settings, attr):
+ # on the command line.
+ v8_target_cpu_transition = transition(
+     implementation = _v8_target_cpu_transition_impl,
+-    inputs = ["//command_line_option:cpu"],
++    inputs = ["@v8//bazel/config:v8_target_cpu", "//command_line_option:cpu"],
+     outputs = ["@v8//bazel/config:v8_target_cpu"],
+ )
+

bazel/repositories.bzl

@@ -29,6 +29,14 @@ def proxy_wasm_cpp_host_repositories():
         sha256 = "c6966ec828da198c5d9adbaa94c05e3a1c7f21bd012a0b29ba8ddbccb2c93b0d",
     )
 
+    maybe(
+        http_archive,
+        name = "bazel-zig-cc",
+        sha256 = "ad6384b4d16ebb3e5047df6548a195e598346da84e5f320250beb9198705ac81",
+        strip_prefix = "bazel-zig-cc-v0.4.4",
+        url = "https://git.sr.ht/~motiejus/bazel-zig-cc/archive/v0.4.4.tar.gz",
+    )
+
     maybe(
         http_archive,
         name = "rules_foreign_cc",
@@ -59,10 +67,10 @@ def proxy_wasm_cpp_host_repositories():
     maybe(
         http_archive,
         name = "boringssl",
-        # 2022-01-10 (master-with-bazel)
-        sha256 = "a530919e3141d00d593a0d74cd0f9f88707e35ec58bb62245968fec16cb9257f",
-        strip_prefix = "boringssl-9420fb54116466923afa1f34a23dd8a4a7ddb69d",
-        urls = ["https://github.com/google/boringssl/archive/9420fb54116466923afa1f34a23dd8a4a7ddb69d.tar.gz"],
+        # 2022-02-07 (master-with-bazel)
+        sha256 = "7dec97795a7ac7e3832228e4440ee06cceb18d3663f4580b0840e685281e28a0",
+        strip_prefix = "boringssl-eaa29f431f71b8121e1da76bcd3ddc2248238ade",
+        urls = ["https://github.com/google/boringssl/archive/eaa29f431f71b8121e1da76bcd3ddc2248238ade.tar.gz"],
     )
 
     maybe(