Bazel-获取当前的OS和CPU类型作为要在构建规则中使用的变量

Question

In our current setup, we use Bazel as the overall build tool, but for individual Java projects, we use Maven for building them. An example build rule for a Java project will look like this:

genrule (
    name = "build-core",
    srcs = [
        ":deps-core",
    ],
    outs = [
        "core-1.0.jar",
    ],
    cmd = "rm -rf $(@D)/src && cd project/ && umask 0000"
        + " && mvn -U clean install -Djavacpp.platform=linux-x86_64 -pl :core"
        + " && cp core/target/core-1.0.jar ../$(@D)"
)

As you can notice, we are currently hardcoding the -Djavacpp.platform to linux-x86_64 . Is there a way to get this value automatically from Bazel, maybe as a variable, so that we can use the same build rules to build on MacOSX and Windows systems too?

Answer 1

It would be better to build all of the libraries with Bazel directly, then you would get this behaviour for free. See Migrating from Maven to Bazel .

However, if this is not an option, you can access some of this information using Make Variables :

genrule(
  name = "g",
  outs = [
    "g.txt",
  ],
  cmd = "echo \"$(TARGET_CPU) $(COMPILATION_MODE) $(JAVA) $(JAVABASE)\" > $@",
  toolchains = [
    "@bazel_tools//tools/jdk:current_java_runtime",
  ],
)

I could not find the operating system in these variables, however.

Perhaps a better idea is to use select statements:

genrule(
  name = "f",
  outs = [
    "f.txt",
  ],
  cmd = select({
    "@bazel_tools//src/conditions:darwin": "echo 'macOS' > $@",
    "//conditions:default": "echo 'Linux' > $@",
  }),
)

You would then write a different cmd for each platform.