如何用Bazel genrule为每个include文件添加对应命令行选项

我有一款命令行工具，支持通过重复的--include选项传入多个文件，使用示例如下：

mytool --include=some_include1 --include=some_include2 --include=... source1 source2 ...

我编写了如下Bazel规则：

filegroup(
  name = "include_group",
  srcs = ["some_include1", "some_include2"],
)

filegroup(
  name = "source_group",
  srcs = ["source1", "source2"],
)

genrule(
  name = "myrule",
  srcs = [":include_group"] + [":source_group"],
  outs = ["out.cpp"],
  tools = ["mytool"],
  cmd = "$(location :mytool) --include=$(locations :include_group) $(locations :source_group)"
)

但生成的实际命令行结果不符合预期：

mytool --include=some_include1 some_include2 source1 source2 

可以看到第二个include文件some_include2缺失了--include前缀，需要为include_group中的每个文件都自动添加对应的--include选项。

解决方法 #

方法1：使用Bazel内置的$(foreach)函数 #

直接修改genrule的cmd字段，利用foreach遍历每个include文件并拼接前缀：

genrule(
  name = "myrule",
  srcs = [":include_group", ":source_group"],
  outs = ["out.cpp"],
  tools = ["mytool"],
  cmd = "$(location :mytool) $(foreach include,$(locations :include_group),--include=$(include)) $(locations :source_group)"
)

$(foreach var, list, expr)会遍历list中的每个元素，将var替换为当前元素后展开expr。这里会为每个include文件生成--include=文件路径的字符串，最终所有字符串以空格分隔，完全符合工具的参数要求。

方法2：自定义Starlark规则（适用于复杂场景） #

如果需要更灵活的参数处理或复用逻辑，可以编写自定义Starlark规则。创建mytool_rule.bzl文件：

def _mytool_rule_impl(ctx):
    tool = ctx.executable.tool
    includes = ctx.files.includes
    sources = ctx.files.sources
    output = ctx.outputs.out

    args = ctx.actions.args()
    # 为每个include添加--include前缀
    for include in includes:
        args.add("--include", include.path)
    # 添加所有源文件
    args.add_all(sources)

    ctx.actions.run(
        inputs = includes + sources,
        outputs = [output],
        executable = tool,
        arguments = [args],
    )

mytool_rule = rule(
    implementation = _mytool_rule_impl,
    attrs = {
        "tool": attr.label(executable = True, cfg = "exec", mandatory = True),
        "includes": attr.label_list(allow_files = True, mandatory = True),
        "sources": attr.label_list(allow_files = True, mandatory = True),
        "out": attr.output(mandatory = True),
    },
)

在BUILD文件中加载并使用该规则：

load("//path/to:mytool_rule.bzl", "mytool_rule")

mytool_rule(
    name = "myrule",
    tool = ":mytool",
    includes = [":include_group"],
    sources = [":source_group"],
    out = "out.cpp",
)

这种方式可读性和可维护性更强，适合后续扩展复杂的参数逻辑。

内容的提问来源于stack exchange，提问作者Alexander Chen