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chore: use python.defaults to set rules_python default python version #3301

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Merged
merged 7 commits into from
Sep 28, 2025
Merged

chore: use python.defaults to set rules_python default python version #3301

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ef06820
chore: use python.defaults to set rules_python default python version
rickeylev Sep 28, 2025
c64b904
compute default python version in the same loop
rickeylev Sep 28, 2025
fe8b278
add tests
rickeylev Sep 28, 2025
1c25832
update comments
rickeylev Sep 28, 2025
d0e8ee3
Merge branch 'main' of https://github.com/bazel-contrib/rules_python …
rickeylev Sep 28, 2025
72230e4
remove xtest debugging code
rickeylev Sep 28, 2025
003a4b5
switch is_root=False by default for the mock module function
rickeylev Sep 28, 2025
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6 changes: 5 additions & 1 deletion MODULE.bazel
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Original file line number Diff line number Diff line change
Expand Up @@ -42,8 +42,12 @@ python = use_extension("//python/extensions:python.bzl", "python")
# NOTE: This is not a stable version. It is provided for convenience, but will
# change frequently to track the most recent Python version.
# NOTE: The root module can override this.
# NOTE: There must be a corresponding `python.toolchain()` call for the version
# specified here.
python.defaults(
python_version = "3.11",
)
python.toolchain(
is_default = True,
python_version = "3.11",
)
use_repo(
Expand Down
145 changes: 90 additions & 55 deletions python/private/python.bzl
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Original file line number Diff line number Diff line change
Expand Up @@ -85,46 +85,7 @@ def parse_modules(*, module_ctx, logger, _fail = fail):

config = _get_toolchain_config(modules = module_ctx.modules, _fail = _fail)

default_python_version = None
for mod in module_ctx.modules:
defaults_attr_structs = _create_defaults_attr_structs(mod = mod)
default_python_version_env = None
default_python_version_file = None

# Only the root module and rules_python are allowed to specify the default
# toolchain for a couple reasons:
# * It prevents submodules from specifying different defaults and only
# one of them winning.
# * rules_python needs to set a soft default in case the root module doesn't,
# e.g. if the root module doesn't use Python itself.
# * The root module is allowed to override the rules_python default.
if mod.is_root or (mod.name == "rules_python" and not default_python_version):
for defaults_attr in defaults_attr_structs:
default_python_version = _one_or_the_same(
default_python_version,
defaults_attr.python_version,
onerror = _fail_multiple_defaults_python_version,
)
default_python_version_env = _one_or_the_same(
default_python_version_env,
defaults_attr.python_version_env,
onerror = _fail_multiple_defaults_python_version_env,
)
default_python_version_file = _one_or_the_same(
default_python_version_file,
defaults_attr.python_version_file,
onerror = _fail_multiple_defaults_python_version_file,
)
if default_python_version_file:
default_python_version = _one_or_the_same(
default_python_version,
module_ctx.read(default_python_version_file, watch = "yes").strip(),
)
if default_python_version_env:
default_python_version = module_ctx.getenv(
default_python_version_env,
default_python_version,
)
default_python_version = _compute_default_python_version(module_ctx)

seen_versions = {}
for mod in module_ctx.modules:
Expand Down Expand Up @@ -152,13 +113,7 @@ def parse_modules(*, module_ctx, logger, _fail = fail):
# * rules_python needs to set a soft default in case the root module doesn't,
# e.g. if the root module doesn't use Python itself.
# * The root module is allowed to override the rules_python default.
if default_python_version:
is_default = default_python_version == toolchain_version
if toolchain_attr.is_default and not is_default:
fail("The 'is_default' attribute doesn't work if you set " +
"the default Python version with the `defaults` tag.")
else:
is_default = toolchain_attr.is_default
is_default = default_python_version == toolchain_version

# Also only the root module should be able to decide ignore_root_user_error.
# Modules being depended upon don't know the final environment, so they aren't
Expand All @@ -169,15 +124,15 @@ def parse_modules(*, module_ctx, logger, _fail = fail):
fail("Toolchains in the root module must have consistent 'ignore_root_user_error' attributes")

ignore_root_user_error = toolchain_attr.ignore_root_user_error
elif mod.name == "rules_python" and not default_toolchain and not default_python_version:
# We don't do the len() check because we want the default that rules_python
# sets to be clearly visible.
is_default = toolchain_attr.is_default
elif mod.name == "rules_python" and not default_toolchain:
# This branch handles when the root module doesn't declare a
# Python toolchain
is_default = default_python_version == toolchain_version
else:
is_default = False

if is_default and default_toolchain != None:
_fail_multiple_default_toolchains(
_fail_multiple_default_toolchains_chosen(
first = default_toolchain.name,
second = toolchain_name,
)
Expand Down Expand Up @@ -577,14 +532,24 @@ def _fail_multiple_defaults_python_version_env(first, second):
second = second,
))

def _fail_multiple_default_toolchains(first, second):
def _fail_multiple_default_toolchains_chosen(first, second):
fail(("Multiple default toolchains: only one toolchain " +
"can have is_default=True. First default " +
"can be chosen as a default. First default " +
"was toolchain '{first}'. Second was '{second}'").format(
first = first,
second = second,
))

def _fail_multiple_default_toolchains_in_module(mod, toolchain_attrs):
fail(("Multiple default toolchains: only one toolchain " +
"can have is_default=True.\n" +
"Module '{module}' contains {count} toolchains with " +
"is_default=True: {versions}").format(
module = mod.name,
count = len(toolchain_attrs),
versions = ", ".join(sorted([v.python_version for v in toolchain_attrs])),
))

def _validate_version(version_str, *, _fail = fail):
v = version.parse(version_str, strict = True, _fail = _fail)
if v == None:
Expand Down Expand Up @@ -880,6 +845,72 @@ def _get_toolchain_config(*, modules, _fail = fail):
register_all_versions = register_all_versions,
)

def _compute_default_python_version(mctx):
default_python_version = None
for mod in mctx.modules:
# Only the root module and rules_python are allowed to specify the default
# toolchain for a couple reasons:
# * It prevents submodules from specifying different defaults and only
# one of them winning.
# * rules_python needs to set a soft default in case the root module doesn't,
# e.g. if the root module doesn't use Python itself.
# * The root module is allowed to override the rules_python default.
if not (mod.is_root or mod.name == "rules_python"):
continue

defaults_attr_structs = _create_defaults_attr_structs(mod = mod)
default_python_version_env = None
default_python_version_file = None

for defaults_attr in defaults_attr_structs:
default_python_version = _one_or_the_same(
default_python_version,
defaults_attr.python_version,
onerror = _fail_multiple_defaults_python_version,
)
default_python_version_env = _one_or_the_same(
default_python_version_env,
defaults_attr.python_version_env,
onerror = _fail_multiple_defaults_python_version_env,
)
default_python_version_file = _one_or_the_same(
default_python_version_file,
defaults_attr.python_version_file,
onerror = _fail_multiple_defaults_python_version_file,
)
if default_python_version_file:
default_python_version = _one_or_the_same(
default_python_version,
mctx.read(default_python_version_file, watch = "yes").strip(),
)
if default_python_version_env:
default_python_version = mctx.getenv(
default_python_version_env,
default_python_version,
)

if default_python_version:
break

# Otherwise, look at legacy python.toolchain() calls for a default
toolchain_attrs = mod.tags.toolchain

# Convenience: if one python.toolchain() call exists, treat it as
# the default.
if len(toolchain_attrs) == 1:
default_python_version = toolchain_attrs[0].python_version
else:
sets_default = [v for v in toolchain_attrs if v.is_default]
if len(sets_default) == 1:
default_python_version = sets_default[0].python_version
elif len(sets_default) > 1:
_fail_multiple_default_toolchains_in_module(mod, toolchain_attrs)

if default_python_version:
break

return default_python_version

def _create_defaults_attr_structs(*, mod):
arg_structs = []

Expand Down Expand Up @@ -915,7 +946,11 @@ def _create_toolchain_attr_structs(*, mod, config, seen_versions):

return arg_structs

def _create_toolchain_attrs_struct(*, tag = None, python_version = None, toolchain_tag_count = None):
def _create_toolchain_attrs_struct(
*,
tag = None,
python_version = None,
toolchain_tag_count = None):
if tag and python_version:
fail("Only one of tag and python version can be specified")
if tag:
Expand Down
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