test.bzl

def _build(ctx):
    print(ctx)

def _impl(ctx):
    # Print debug information about the target.
    #    print("Target {} has {} deps".format(ctx.label, len(ctx.attr.deps)))
    #
    #    # For each target in deps, print its label and files.
    #    for i, d in enumerate(ctx.attr.deps):
    #        print(" {}. label = {}".format(i + 1, d.label))
    #
    #        # A label can represent any number of files (possibly 0).
    #        print("    files = " + str([f.path for f in d.files.to_list()]))

    # For debugging, consider using `dir` to explore the existing fields.
    print(dir(ctx))  # prints all the fields and methods of ctx
    print(dir(ctx.attr.target))  # prints all the attributes of the rule
    ctx.actions.run(
        ctx.attr.target,
    )

printer = rule(
    implementation = _impl,
    attrs = {
        # Do not declare "name": It is added automatically.
        "number": attr.int(default = 1),
        "deps": attr.label_list(allow_files = True),
    },
)

build = rule(
    implementation = _impl,
    attrs = {
        "target": attr.label_list(),
    },
)