feat(config_settings): accept minor versions of Python in `python_ver…

…sion` flag

Currently user has to specify a full (x.y.z) version of Python when setting the
`python_version` flag. When they upgrade `rules_python` or change `MINOR_MAPPING`
in some other way, user has to update the flag's value to keep it in sync with
`MINOR_MAPPING`. This patch allows `python_version` flag to accept minor (x.y)
versions and resolves them to the corresponding full versions using `MINOR_MAPPING`.

CHANGELOG.md

@@ -94,6 +94,8 @@ Breaking changes:
 * (utils) Added a `pip_utils` struct with a `normalize_name` function to allow users
   to find out how `rules_python` would normalize a PyPI distribution name.
 
+* (config_settings) The `python_version` flag now accepts minor Python versions.
+
 ## [0.26.0] - 2023-10-06
 
 ### Changed

python/config_settings/BUILD.bazel

@@ -1,4 +1,4 @@
-load("//python:versions.bzl", "TOOL_VERSIONS")
+load("//python:versions.bzl", "MINOR_MAPPING", "TOOL_VERSIONS")
 load(":config_settings.bzl", "construct_config_settings")
 
 filegroup(
@@ -10,4 +10,7 @@ filegroup(
     visibility = ["//python:__pkg__"],
 )
 
-construct_config_settings(python_versions = TOOL_VERSIONS.keys())
+construct_config_settings(
+    minor_mapping = MINOR_MAPPING,
+    python_versions = TOOL_VERSIONS.keys(),
+)

python/config_settings/config_settings.bzl

@@ -15,26 +15,52 @@
 """This module is used to construct the config settings in the BUILD file in this same package.
 """
 
+load("@bazel_skylib//lib:selects.bzl", "selects")
 load("@bazel_skylib//rules:common_settings.bzl", "string_flag")
 
 # buildifier: disable=unnamed-macro
-def construct_config_settings(python_versions):
+def construct_config_settings(minor_mapping, python_versions):
     """Constructs a set of configs for all Python versions.
 
     Args:
-        python_versions: The Python versions supported by rules_python.
+        minor_mapping: mapping from minor (x.y) versions to the corresponding full (x.y.z) versions.
+        python_versions: list of full (x.y.z) Python versions supported by rules_python.
     """
+
+    minor_versions = list(minor_mapping.keys())
+    allowed_flag_values = python_versions + minor_versions
+
     string_flag(
         name = "python_version",
         build_setting_default = python_versions[0],
-        values = python_versions,
+        values = allowed_flag_values,
         visibility = ["//visibility:public"],
     )
 
-    for python_version in python_versions:
-        python_version_constraint_setting = "is_python_" + python_version
+    for flag_value in allowed_flag_values:
+        flag_value_constraint_setting = "python_version_flag_equals_" + flag_value
         native.config_setting(
+            name = flag_value_constraint_setting,
+            flag_values = {":python_version": flag_value},
+            visibility = ["//visibility:public"],
+        )
+
+    flag_values_that_enable_version = {
+        full_version: [full_version]
+        for full_version in python_versions
+    }
+
+    for minor_version, full_version in minor_mapping.items():
+        flag_values_that_enable_version[full_version].append(minor_version)
+
+    for full_version, flag_values in flag_values_that_enable_version.items():
+        python_version_constraint_setting = "is_python_" + full_version
+        flag_value_constraints = [
+            ":python_version_flag_equals_" + flag_value
+            for flag_value in flag_values
+        ]
+        selects.config_setting_group(
             name = python_version_constraint_setting,
-            flag_values = {":python_version": python_version},
+            match_any = flag_value_constraints,
             visibility = ["//visibility:public"],
         )