使用Bazel构建时，不兼容平台上的目标为何未被跳过？

根据Bazel官方文档，当目标与指定平台不兼容时应被跳过。但执行bazel build --platforms=//:qnx-x86_64 //...时，标记为仅兼容Linux的Rust目标未被跳过，反而出现工具链匹配错误：

ERROR: ./hello_world_rust/BUILD:3:12: While resolving toolchains for target //hello_world_rust:hello_world_rust: No matching toolchains found for types @bazel_tools//tools/cpp:toolchain_type, @rules_rust//rust:toolchain_type.

环境：bazelisk + Bazel 6.1.0，主机系统为Ubuntu。

相关文件内容 #

./BUILD #

platform(
    name = "qnx-x86_64",
    constraint_values = [
        "@platforms//os:qnx",
        "@platforms//cpu:x86_64",
    ],
    visibility = ["//visibility:public"],
)

./WORKSPACE #

load("//:repositories.bzl", "load_bazel_skylib_repositories", "load_rules_rust_repositories")
load_bazel_skylib_repositories()
load_rules_rust_repositories()
load("//:setup.bzl", "setup_rules_rust_repositories")
setup_rules_rust_repositories()

./hello_world_rust/BUILD #

load("@rules_rust//rust:defs.bzl", "rust_binary")

rust_binary(
    name = "hello_world_rust",
    srcs = ["src/main.rs"],
    edition = "2021",
    target_compatible_with = [
        "@platforms//os:linux",
        "@platforms//cpu:x86_64",
    ],
)

./hello_world_rust/Cargo.toml #

[package]
name = "hello_world_rust"
version = "0.1.0"
edition = "2021"

./hello_world_rust/src/main.rs #

fn main() { println!("Hello, World!"); }

./repositories.bzl #

load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

VERSION = "1.3.0"
def load_bazel_skylib_repositories():
    maybe(
        name = "bazel_skylib",
        repo_rule = http_archive,
        urls = [
            "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/{version}/bazel-skylib-{version}.tar.gz".format(version = VERSION),
            "https://github.com/bazelbuild/bazel-skylib/releases/download/{version}/bazel-skylib-{version}.tar.gz".format(version = VERSION),
        ],
        sha256 = "74d544d96f4a5bb630d465ca8bbcfe231e3594e5aae57e1edbf17a6eb3ca2506",
    )

RULES_RUST_VERSION = "0.18.0"
def load_rules_rust_repositories():
    maybe(
        name = "rules_rust",
        repo_rule = http_archive,
        sha256 = "2466e5b2514772e84f9009010797b9cd4b51c1e6445bbd5b5e24848d90e6fb2e",
        urls = [
            "https://mirror.bazel.build/github.com/bazelbuild/rules_rust/releases/download/{version}/rules_rust-v{version}.tar.gz".format(version = RULES_RUST_VERSION),
            "https://github.com/bazelbuild/rules_rust/releases/download/{version}/rules_rust-v{version}.tar.gz".format(version = RULES_RUST_VERSION),
        ],
    )

./setup.bzl #

load(
    "@rules_rust//rust:repositories.bzl",
    "rules_rust_dependencies",
    "rust_register_toolchains",
    "rust_repositories",
)

def setup_rules_rust_repositories():
    rules_rust_dependencies()
    rust_repositories()
    rust_register_toolchains(versions = ["1.61.0"], edition = "2021")

原因分析 #

Bazel的工具链解析逻辑优先级高于目标兼容性检查：先检查是否存在适配指定平台的工具链，再判断目标是否与平台兼容。这里指定QNX平台后，Bazel找不到对应的Rust和C++工具链，直接在工具链解析阶段报错，根本没走到跳过不兼容目标的步骤。

解决方案 #

方案1：注册QNX适配工具链（需实际构建QNX目标） #

如果需要为QNX平台构建目标，需补充适配的工具链。对于rules_rust，可通过rust_register_toolchains的target_triples参数指定QNX的目标三元组（如x86_64-unknown-nto-qnx710），同时确保本地有对应版本的Rust工具链。

方案2：启用提前兼容性检查（仅跳过不兼容目标） #

添加--incompatible_enable_skip_target_compatibility_check构建标志，让Bazel先判断目标是否兼容平台，再解析工具链。不兼容的目标会直接被跳过，不会触发工具链错误。可以在命令中直接使用：

bazel build --platforms=//:qnx-x86_64 --incompatible_enable_skip_target_compatibility_check //...

也可以在项目根目录的.bazelrc中全局配置：

build --incompatible_enable_skip_target_compatibility_check

方案3：直接排除不兼容目标 #

在构建命令中用--exclude_patterns跳过特定目标：

bazel build --platforms=//:qnx-x86_64 //... --exclude_patterns=//hello_world_rust:*

内容的提问来源于stack exchange，提问作者nnnmmm