chore: ensure we don't try to compile any C++ code (aspect-build#16)

* chore: ensure we don't try to compile any C++ code

We don't have any C++ code in this repo, and want to make sure that our examples don't transitively depend on building protoc from source.

* Update MODULE.bazel

Co-authored-by: Fabian Meumertzheim <fabian@meumertzhe.im>

* Disable CGo (aspect-build#17)

* chore: buildifier

---------

Co-authored-by: Fabian Meumertzheim <fabian@meumertzhe.im>

.bazelrc

@@ -14,6 +14,9 @@ common --action_env=RULES_PYTHON_ENABLE_PYSTAR=0
 # https://bazelbuild.slack.com/archives/C014RARENH0/p1691158021917459?thread_ts=1691156601.420349&cid=C014RARENH0
 common --check_direct_dependencies=off
 
+# Force rules_go to disable CGO even though we have a (fake) C++ toolchain registered.
+common --host_platform=//:no_cgo_host_platform
+
 # Load any settings specific to the current user.
 # .bazelrc.user should appear in .gitignore so that settings are not shared with team members
 # This needs to be last statement in this

BUILD.bazel

@@ -0,0 +1,8 @@
+load("@platforms//host:constraints.bzl", "HOST_CONSTRAINTS")
+
+platform(
+    name = "no_cgo_host_platform",
+    constraint_values = HOST_CONSTRAINTS + [
+        "@rules_go//go/toolchain:cgo_off",
+    ],
+)

MODULE.bazel

@@ -9,7 +9,7 @@ module(
 bazel_dep(name = "bazel_features", version = "1.9.0")
 bazel_dep(name = "bazel_skylib", version = "1.4.1")
 bazel_dep(name = "rules_proto", version = "6.0.0")
-bazel_dep(name = "platforms", version = "0.0.8")
+bazel_dep(name = "platforms", version = "0.0.10")
 
 protoc = use_extension("//protoc:extensions.bzl", "protoc")
 protoc.toolchain(
@@ -20,6 +20,12 @@ use_repo(protoc, "com_google_protobuf", "toolchains_protoc_hub")
 
 register_toolchains("@toolchains_protoc_hub//:all")
 
+# Assert no CC compilation occurs
+register_toolchains(
+    "//tools/toolchains:all",
+    dev_dependency = True,
+)
+
 bazel_dep(name = "aspect_bazel_lib", version = "1.32.1", dev_dependency = True)
 bazel_dep(name = "buildifier_prebuilt", version = "6.1.2", dev_dependency = True)
 bazel_dep(name = "aspect_rules_py", version = "0.7.1", dev_dependency = True)

tools/toolchains/BUILD.bazel

@@ -0,0 +1,31 @@
+"""Define a non-functional cc toolchain.
+
+To fail-fast in cases where we are forced to compile third-party C++ code,
+define a cc toolchain that doesn't work, by using 'false' as the compiler.
+See https://bazel.build/tutorials/ccp-toolchain-config
+"""
+
+load("defs.bzl", "cc_toolchain_config")
+
+filegroup(name = "empty")
+
+cc_toolchain_config(name = "noop_toolchain_config")
+
+cc_toolchain(
+    name = "noop_toolchain",
+    all_files = ":empty",
+    compiler_files = ":empty",
+    dwp_files = ":empty",
+    linker_files = ":empty",
+    objcopy_files = ":empty",
+    strip_files = ":empty",
+    supports_param_files = 0,
+    toolchain_config = ":noop_toolchain_config",
+    toolchain_identifier = "noop-toolchain",
+)
+
+toolchain(
+    name = "cc_toolchain",
+    toolchain = ":noop_toolchain",
+    toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
+)

tools/toolchains/defs.bzl

@@ -0,0 +1,20 @@
+"Configure a cc toolchain to call 'false' if used."
+
+def _impl(ctx):
+    return cc_common.create_cc_toolchain_config_info(
+        ctx = ctx,
+        toolchain_identifier = "noop-toolchain",
+        host_system_name = "local",
+        target_system_name = "local",
+        target_cpu = "k8",
+        target_libc = "unknown",
+        compiler = "false",
+        abi_version = "unknown",
+        abi_libc_version = "unknown",
+    )
+
+cc_toolchain_config = rule(
+    implementation = _impl,
+    attrs = {},
+    provides = [CcToolchainConfigInfo],
+)