clarify code and use different concepts for label reusing

python/private/config_settings.bzl

@@ -69,19 +69,31 @@ def _flag_values(python_versions):
 
 VERSION_FLAG_VALUES = _flag_values(TOOL_VERSIONS.keys())
 
-def is_python_config_setting(name, *, python_version, match_any = None, **kwargs):
+def is_python_config_setting(name, *, python_version, reuse_conditions = None, **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.
 
+ The matching of the 'python_version' flag depends on the value passed in
+ `python_version` and here is the example for `3.8` (but the same applies
+ to other python versions present in @//python:versions.bzl#TOOL_VERSIONS):
+ * "3.8" -> ["3.8", "3.8.1", "3.8.2", ..., "3.8.19"] # All 3.8 versions
+ * "3.8.2" -> ["3.8.2"] # Only 3.8.2
+ * "3.8.19" -> ["3.8.19", "3.8"] # The latest version should also match 3.8 so
+ as when the `3.8` toolchain is used we just use the latest `3.8` toolchain.
+ this makes the `select("is_python_3.8.19")` work no matter how the user
+ specifies the latest python version to use.
+
  Args:
  name: name for the target that will be created to be used in select statements.
- python_version: The python_version to be passed in the `flag_values` in the `config_setting`.
- match_any: The labels that should be used for matching the extra
- versions, which get passed to `config_setting_group.match_any`. If
- empty or None, this macro will create config settings necessary to
- match the `python_version` value.
+ python_version: The python_version to be passed in the `flag_values` in the
+ `config_setting`. Depending on the version, the matching python version list
+ can be as described above.
+ reuse_conditions: A dict of version to version label for which we should
+ reuse config_setting targets instead of creating them from scratch. This
+ is useful when using is_python_config_setting multiple times in the
+ same package with the same `major.minor` python versions.
  **kwargs: extra kwargs passed to the `config_setting`.
  """
  if python_version not in name:
@@ -90,34 +102,38 @@ def is_python_config_setting(name, *, python_version, match_any = None, **kwargs
  if python_version not in VERSION_FLAG_VALUES:
  fail("The 'python_version' must be known to 'rules_python', choose from the values: {}".format(VERSION_FLAG_VALUES.keys()))
 
- flag_values = {
- _PYTHON_VERSION_FLAG: python_version,
- }
-
  python_versions = VERSION_FLAG_VALUES[python_version]
- if len(python_versions) == 1 and not match_any:
+ if len(python_versions) == 1:
  native.config_setting(
  name = name,
- flag_values = flag_values,
+ flag_values = {
+ _PYTHON_VERSION_FLAG: python_version,
+ },
  **kwargs
  )
  return
 
- if not match_any:
- create_config_settings = {
- "_{}".format(name).replace(python_version, version): {_PYTHON_VERSION_FLAG: version}
- for version in python_versions
- }
- match_any = list(create_config_settings.keys())
- else:
- setting_name = "_" + name if len(python_versions) > 1 else name
- create_config_settings = {setting_name: flag_values}
- if setting_name not in match_any:
- # Here we expect the user to supply us with a name of the label that
- # would be created by this function. This needs to be the case because
- # the VERSION_FLAG_VALUES values contain the all of the versions that
- # have to be matched.
- fail("'{}' must be present in 'match_any'".format(setting_name))
+ reuse_conditions = reuse_conditions or {}
+ create_config_settings = {
+ "_{}".format(name).replace(python_version, version): {_PYTHON_VERSION_FLAG: version}
+ for version in python_versions
+ if not reuse_conditions or version not in reuse_conditions
+ }
+ match_any = list(create_config_settings.keys())
+ for version, condition in reuse_conditions.items():
+ if len(VERSION_FLAG_VALUES[version]) == 1:
+ match_any.append(condition)
+ continue
+
+ # Convert the name to an internal label that this function would create,
+ # so that we are hitting the config_setting and not the config_setting_group.
+ condition = Label(condition)
+ if hasattr(condition, "same_package_label"):
+ condition = condition.same_package_label("_" + condition.name)
+ else:
+ condition = condition.relative("_" + condition.name)
+
+ match_any.append(condition)
 
  for name_, flag_values_ in create_config_settings.items():
  native.config_setting(
@@ -162,25 +178,13 @@ def construct_config_settings(name = None): # buildifier: disable=function-docs
  )
 
  for version, matching_versions in VERSION_FLAG_VALUES.items():
- match_any = None
- if len(matching_versions) > 1:
- match_any = [
- # 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 with generating
- # fewer targets overall.
- ("_is_python_{}" if len(VERSION_FLAG_VALUES[v]) > 1 else "is_python_{}").format(v)
- for v in matching_versions
- ]
-
  is_python_config_setting(
  name = "is_python_{}".format(version),
  python_version = version,
- # NOTE @aignas 2024-03-16: if we don't have this, then we may create duplicate
- # targets. I think this should be improved, but I haven't figured out how yet
- # and I ran out of time.
- #
- # The fact that this parameter is needed here, suggests that we may need to
- # think of a better abstraction here.
- match_any = match_any,
+ reuse_conditions = {
+ v: native.package_relative_label("is_python_{}".format(v))
+ for v in matching_versions
+ if v != version
+ },
  visibility = ["//visibility:public"],
  )