blob: 0401a454b33ff3da69faf823e353b507c952b1b7 [file] [log] [blame]
This file contains a way to set flags from BUILD.bazel instead of requiring users to set them from
the CLI.
It is based off of
_bool_flags = [
_string_flags = [
_string_list_flags = [
# These are the flags that we support setting via set_flags
_flags = _bool_flags + _string_flags + _string_list_flags
def _flag_transition_impl(settings, attr):
rv = {}
for key in settings:
# Get the short form of the name. This the short form used as the keys in the
# set_flags dictionary.
flag_name = key.split(":")[1]
# If there is an entry in set_flags for the short-version of a flag, use that
# value or values. If not, use whatever value is set via flags.
flag_setting = attr.set_flags.get(flag_name, settings[key])
if key in _string_list_flags:
if type(flag_setting) == "list":
rv[key] = flag_setting
rv[key] = [flag_setting] # This usually happens when the default value is used.
elif key in _string_flags:
if type(flag_setting) == "list":
rv[key] = flag_setting[0]
rv[key] = flag_setting # we know flag_setting is a string (e.g. the default).
elif key in _bool_flags:
if type(flag_setting) == "list":
rv[key] = flag_setting[0] == "True"
rv[key] = flag_setting # flag_setting will be a boolean, the default
return rv
# This defines a Starlark transition and which flags it reads and writes.
_flag_transition = transition(
implementation = _flag_transition_impl,
inputs = _flags,
outputs = _flags,
# The implementation of transition_rule: all this does is copy the cc_binary's output to
# its own output and propagate its runfiles and executable to use for "$ bazel run".
# This makes transition_rule as close to a pure wrapper of cc_binary as possible.
def _transition_rule_impl(ctx):
actual_binary = ctx.attr.actual_binary[0]
outfile = ctx.actions.declare_file(
cc_binary_outfile = actual_binary[DefaultInfo].files.to_list()[0]
inputs = [cc_binary_outfile],
outputs = [outfile],
command = "cp %s %s" % (cc_binary_outfile.path, outfile.path),
return [
executable = outfile,
data_runfiles = actual_binary[DefaultInfo].data_runfiles,
# The purpose of this rule is to take a "set_flags" attribute, invoke a transition that sets
# any of _flags to the specified values, then depend on a cc_binary whose deps will be able
# to select() on those flags as if the user had set them via the CLI.
transition_rule = rule(
implementation = _transition_rule_impl,
attrs = {
# set_flags is a dictionary with the keys being the short-form of a flag name
# (e.g. the part that comes after the colon) and the value being a list of values
# that the flag should be set to, regardless of the relevant CLI flags.
"set_flags": attr.string_list_dict(),
# This is the cc_binary whose deps will select() on that feature.
# Note specifically how it is modified with _flag_transition, which
# ensures that the flags propagates down the graph.
"actual_binary": attr.label(cfg = _flag_transition),
# This is a stock Bazel requirement for any rule that uses Starlark
# transitions. It's okay to copy the below verbatim for all such rules.
# The purpose of this requirement is to give the ability to restrict
# which packages can invoke these rules, since Starlark transitions
# make much larger graphs possible that can have memory and performance
# consequences for your build. The allowlist defaults to "everything".
# But you can redefine it more strictly if you feel that's prudent.
"_allowlist_function_transition": attr.label(
default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
# Making this executable means it works with "$ bazel run".
executable = True,
def cc_binary_with_flags(name, set_flags = {}, **kwargs):
"""Builds a cc_binary as if set_flags were set on the CLI.
name: string, the name for the rule that is the binary, but with the flags changed via
a transition. Any dependents should use this name.
set_flags: dictionary of string to list of strings. The keys should be the name of the
flag, and the values should be the desired valid settings for that flag.
**kwargs: Any flags that a cc_binary normally takes.
cc_binary_name = name + "_native_binary"
name = name,
actual_binary = ":%s" % cc_binary_name,
set_flags = set_flags,
testonly = kwargs.get("testonly", False),
name = cc_binary_name,