ToolchainResolution为错误的平台选择工具链

Question

我定义了一个新的锈蚀工具链如下(从生锈分叉)：

toolchain(
    name = "toolchain_for_armv7-linux-androideabi",
    exec_compatible_with = ["@platforms//cpu:x86_64", "@platforms//os:windows"],
    target_compatible_with = ["@platforms//cpu:armv7", "@platforms//os:android"],
    toolchain = "@rust_windows_x86_64//:toolchain_for_armv7-linux-androideabi_impl",
    toolchain_type = "@rules_rust//rust:toolchain",
)

还有一个现有的工具链，定义如下：

toolchain(
    name = "toolchain_for_x86_64-apple-darwin",
    exec_compatible_with = ["@platforms//cpu:x86_64", "@platforms//os:osx"],
    target_compatible_with = ["@platforms//cpu:x86_64", "@platforms//os:osx"],
    toolchain = "@rust_darwin_x86_64//:toolchain_for_x86_64-apple-darwin_impl",
    toolchain_type = "@rules_rust//rust:toolchain",
)

并为该平台建立一个目标：

bazel build --toolchain_resolution_debug=@rules_rust//rust:toolchain --experimental_platforms_api vrst-test/android --platforms=//platforms:android_armv7

下面是ToolchainResolution调试信息的片段：

INFO: ToolchainResolution:   Type @rules_rust//rust:toolchain: target platform @local_config_platform//:host: execution @local_config_platform//:host: Selected toolchain @rust_darwin_x86_64//:toolchain_for_x86_64-apple-darwin_impl
INFO: ToolchainResolution:     Type @rules_rust//rust:toolchain: target platform @local_config_platform//:host: Rejected toolchain @rust_darwin_x86_64//:toolchain_for_armv7-linux-androideabi_impl; mismatching values: armv7, android

由于某些原因，目标平台是@local_config_platform//:host，尽管我将该平台显式地指定为android_armv7，定义如下：

platform(
    name = "android_armv7",
    constraint_values = [
      "@platforms//cpu:armv7",
      "@platforms//os:android",
    ],
)```

Answer 1

Bazel解析--platforms指定的目标平台和--host_platform指定的主机平台的工具链。如果您实际上希望为toolchain_for_armv7-linux-androideabi构建主机工具，则需要设置--host_platform。