从bazel中的config_setting获取变量

Question

我定义了以下config_setting：

config_setting(
    name = "perception_env",
    values = {"perception": "true"},
)

print(perception_env)

然而，我似乎不能打印变量，它说它不存在。

Answer 1

config_setting仅用于在select()中选择不同的可能值。config_setting实际上没有值，它更多地是变量( Bazel标志、Starlark定义的标志、平台约束)及其值的关联。values属性基本上用于标志值(“感知”必须是bazel标志)。

例如,

config_setting(
    name = "my_config_setting_opt",
    values = {"compilation_mode": "opt"}
)

config_setting(
    name = "config_setting_dbg",
    values = {"compilation_mode": "dbg"}
)

config_setting(
    name = "config_setting_fastbuild",
    values = {"compilation_mode": "fastbuild"}
)

genrule(
  name = "gen_out",
  outs = ["out"],
  cmd = select({
    ":my_config_setting_opt": "echo Opt mode > $@",
    ":config_setting_dbg": "echo Dbg mode > $@",
    ":config_setting_fastbuild": "echo Fastbuild mode > $@",
  }),
)

3 config_settings声明--compilation_mode标志的3种不同的关联，每个可能的值都有一个(参见https://bazel.build/docs/user-manual#compilation-mode)

然后，select()为select() gen_out的cmd属性声明3个不同的可能值。然后将--compilation_mode标志设置为不同的值，选择cmd的值：

$ bazel build out --compilation_mode=dbg && cat bazel-bin/out
INFO: Build option --compilation_mode has changed, discarding analysis cache.
INFO: Analyzed target //:out (0 packages loaded, 11 targets configured).
INFO: Found 1 target...
Target //:out up-to-date:
  bazel-bin/out
INFO: Elapsed time: 0.145s, Critical Path: 0.01s
INFO: 2 processes: 1 internal, 1 linux-sandbox.
INFO: Build completed successfully, 2 total actions
Dbg mode

$ bazel build out --compilation_mode=opt && cat bazel-bin/out
INFO: Build option --compilation_mode has changed, discarding analysis cache.
INFO: Analyzed target //:out (0 packages loaded, 11 targets configured).
INFO: Found 1 target...
Target //:out up-to-date:
  bazel-bin/out
INFO: Elapsed time: 0.111s, Critical Path: 0.01s
INFO: 2 processes: 1 internal, 1 linux-sandbox.
INFO: Build completed successfully, 2 total actions
Opt mode

$ bazel build out --compilation_mode=fastbuild && cat bazel-bin/out
INFO: Build option --compilation_mode has changed, discarding analysis cache.
INFO: Analyzed target //:out (0 packages loaded, 11 targets configured).
INFO: Found 1 target...
Target //:out up-to-date:
  bazel-bin/out
INFO: Elapsed time: 0.145s, Critical Path: 0.01s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
Fastbuild mode