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internal(config_settings): make config_setting creation reusable
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The PR #1743 explored the idea of creating extra config settings for
each target platform that our toolchain is targetting, however that has
a drawback of not being usable in `bzlmod` if someone built Python for
a platform that we don't provide a toolchain for and tried to use the
`pip.parse` machinery with that by providing the
`python_interpreter_target`. That is a niche usecase, but `rules_python`
is a core ruleset that should only provide abstractions/helpers that
work in all cases or make it possible to extend things.

This explores a way to decouple the definition of the available
`config_settings` values and how they are constructed by adding an extra
`is_python_config_setting` macro, that could be used to declare the
config settings from within the `pip.parse` hub repo. This makes the
work in #1744 to support whl-only hub repos more self-contained.

Supersedes #1743.
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@aignas
aignas committed Feb 12, 2024
1 parent a5e17e6 commit d2db50e
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32 changes: 27 additions & 5 deletions python/config_settings/BUILD.bazel
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
load("//python:versions.bzl", "TOOL_VERSIONS")
load(":config_settings.bzl", "construct_config_settings")
load("@bazel_skylib//rules:common_settings.bzl", "string_flag")
load(":config_settings.bzl", "VERSION_FLAG_VALUES", "is_python_config_setting")

filegroup(
name = "distribution",
Expand All @@ -10,7 +10,29 @@ filegroup(
visibility = ["//python:__pkg__"],
)

construct_config_settings(
name = "construct_config_settings",
python_versions = TOOL_VERSIONS.keys(),
string_flag(
name = "python_version",
# TODO: The default here should somehow match the MODULE config. Until
# then, use the empty string to indicate an unknown version. This
# also prevents version-unaware targets from inadvertently matching
# a select condition when they shouldn't.
build_setting_default = "",
values = [""] + VERSION_FLAG_VALUES.keys(),
visibility = ["//visibility:public"],
)

[
is_python_config_setting(
name = "is_python_{}".format(version),
flag_values = {":python_version": version},
match_extra = [
# Use the internal labels created by this macro in order to handle matching
# 3.8 config value if using the 3.8 version from MINOR_MAPPING. If we used the
# public labels we would have a circular dependency loop.
("_is_python_{}" if VERSION_FLAG_VALUES[x] else "is_python_{}").format(x)
for x in extras
],
visibility = ["//visibility:public"],
)
for version, extras in VERSION_FLAG_VALUES.items()
]
174 changes: 89 additions & 85 deletions python/config_settings/config_settings.bzl
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Original file line number Diff line number Diff line change
Expand Up @@ -16,104 +16,108 @@
"""

load("@bazel_skylib//lib:selects.bzl", "selects")
load("@bazel_skylib//rules:common_settings.bzl", "string_flag")
load("//python:versions.bzl", "MINOR_MAPPING")
load("//python:versions.bzl", "MINOR_MAPPING", "TOOL_VERSIONS")

def construct_config_settings(name, python_versions):
"""Constructs a set of configs for all Python versions.
def _ver_key(s):
_, _, s = s.partition(".") # All are 3
minor, _, s = s.partition(".")
micro, _, s = s.partition(".")
return 100* int(minor) + int(micro)

def _flag_values(python_versions):
"""Construct a map of python_version to a list of toolchain values.
This mapping maps the concept of a config setting to a list of compatible toolchain versions.
For using this in the code, the VERSION_FLAG_VALUES should be used instead.
Args:
name: str, unused; only specified to satisfy buildifier lint checks
and allow programatic modification of the target.
python_versions: list of all (x.y.z) Python versions supported by rules_python.
"""
python_versions: A list of all versions.
Returns:
A map with config settings as keys and values as extra flag values to be included in
the config_setting_group if they should be also matched, which is used for generating
correct entries for matching the latest 3.8 version, etc.
"""
# Maps e.g. "3.8" -> ["3.8.1", "3.8.2", etc]
minor_to_micro_versions = {}

allowed_flag_values = []
for micro_version in python_versions:
minor, _, _ = micro_version.rpartition(".")
minor_to_micro_versions.setdefault(minor, []).append(micro_version)
allowed_flag_values.append(micro_version)

allowed_flag_values.extend(list(minor_to_micro_versions))

string_flag(
name = "python_version",
# TODO: The default here should somehow match the MODULE config. Until
# then, use the empty string to indicate an unknown version. This
# also prevents version-unaware targets from inadvertently matching
# a select condition when they shouldn't.
build_setting_default = "",
values = [""] + sorted(allowed_flag_values),
visibility = ["//visibility:public"],
)
ret = {}

for micro_version in sorted(python_versions, key=_ver_key):
minor_version, _, _ = micro_version.rpartition(".")

for minor_version, micro_versions in minor_to_micro_versions.items():
# This matches the raw flag value, e.g. --//python/config_settings:python_version=3.8
# It's private because matching the concept of e.g. "3.8" value is done
# using the `is_python_X.Y` config setting group, which is aware of the
# minor versions that could match instead.
equals_minor_version_name = "_python_version_flag_equals_" + minor_version
native.config_setting(
name = equals_minor_version_name,
flag_values = {":python_version": minor_version},
)
matches_minor_version_names = [equals_minor_version_name]
ret.setdefault(minor_version, []).append(micro_version)

# Ensure that is_python_3.9.8 is matched if python_version is set
# to 3.9 if MINOR_MAPPING points to 3.9.8
default_micro_version = MINOR_MAPPING[minor_version]
ret[micro_version] = [minor_version] if default_micro_version == micro_version else []

return ret

VERSION_FLAG_VALUES = _flag_values(TOOL_VERSIONS.keys())

for micro_version in micro_versions:
is_micro_version_name = "is_python_" + micro_version
if default_micro_version != micro_version:
native.config_setting(
name = is_micro_version_name,
flag_values = {":python_version": micro_version},
visibility = ["//visibility:public"],
)
matches_minor_version_names.append(is_micro_version_name)
continue

# Ensure that is_python_3.9.8 is matched if python_version is set
# to 3.9 if MINOR_MAPPING points to 3.9.8
equals_micro_name = "_python_version_flag_equals_" + micro_version
native.config_setting(
name = equals_micro_name,
flag_values = {":python_version": micro_version},
)

# An alias pointing to an underscore-prefixed config_setting_group
# is used because config_setting_group creates
# `is_{minor}_N` targets, which are easily confused with the
# `is_{minor}.{micro}` (dot) targets.
selects.config_setting_group(
name = "_" + is_micro_version_name,
match_any = [
equals_micro_name,
equals_minor_version_name,
],
)
native.alias(
name = is_micro_version_name,
actual = "_" + is_micro_version_name,
visibility = ["//visibility:public"],
)
matches_minor_version_names.append(equals_micro_name)

# This is prefixed with an underscore to prevent confusion due to how
# config_setting_group is implemented and how our micro-version targets
# are named. config_setting_group will generate targets like
# "is_python_3.10_1" (where the `_N` suffix is len(match_any).
# Meanwhile, the micro-version tarets are named "is_python_3.10.1" --
# just a single dot vs underscore character difference.
selects.config_setting_group(
name = "_is_python_" + minor_version,
match_any = matches_minor_version_names,
def is_python_config_setting(name, flag_values, match_extra, **kwargs):
"""Create a config setting for matching 'python_version' configuration flag.
This function is mainly intended for internal use within the `whl_library` and `pip_parse`
machinery.
Args:
name: name for the target that will be created to be used in select statements.
flag_values: The flag_values in the `config_setting`.
match_extra: The extra flag values that we should matched when the `name` is used
in the config setting. You can either pass a list of labels that will be included
in the bazel-skylib selects.config_setting_group match_any clause or it can be a
dict[str, dic], where the keys are the names of the extra config_setting targets
to be created and the value is the `flag_values` attribute.
**kwargs: extra kwargs passed to the `config_setting`
"""
visibility = kwargs.pop("visibility", [])
if not match_extra:
native.config_setting(
name = name,
flag_values = flag_values,
visibility = visibility,
**kwargs,
)
return

native.alias(
name = "is_python_" + minor_version,
actual = "_is_python_" + minor_version,
visibility = ["//visibility:public"],
create_config_settings = {"_" + name: flag_values}
match_any = ["_" + name]
if type(match_extra) == type([]):
match_any.extend(match_extra)
elif type(match_extra) == type({}):
match_any.extend(match_extra.keys())
create_config_settings.update(match_extra)
else:
fail("unsupported match_extra type, can be either a list or a dict of dicts")

# Create all of the necessary config setting values for the config_setting_group
for name_, flag_values_ in create_config_settings.items():
native.config_setting(
name = name_,
flag_values = flag_values_,
# We need to pass the visibility here because of how `config_setting_group` is
# implemented, it is using the internal aliases here, hence the need for making
# them with the same visibility as the `alias` itself.
visibility = visibility,
**kwargs,
)

# An alias pointing to an underscore-prefixed config_setting_group
# is used because config_setting_group creates
# `is_{version}_N` targets, which are easily confused with the
# `is_{minor}.{micro}` (dot) targets.
selects.config_setting_group(
name = "_{}_group".format(name),
match_any = match_any,
visibility = ["//visibility:private"],
)
native.alias(
name = name,
actual = "_{}_group".format(name),
visibility = visibility,
)

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