feat(config_settings): allow matching minor version of python_version flag (#1555)

Currently a user has to specify a full (x.y.z) version of Python when
setting the `//python/config_settings: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 adds micro-version agnostic config settings to allow matching the
minor version.
For example e.g. `//python/config_settings:is_python_3.8` will match any
of
`3.8.1, 3.8.2, ...' (or whatever other versions are listed in
`TOOL_VERSIONS`)

---------

Co-authored-by: Richard Levasseur <[email protected]>

Author: dizzy57

CHANGELOG.md

@@ -60,6 +60,10 @@ A brief description of the categories of changes:
   `python_register_toolchains`.
   Note that this only available on the Starlark implementation of the provider.
 
+* (config_settings) Added `//python/config_settings:is_python_X.Y` config
+  settings to match on minor Python version. These settings match any `X.Y`
+  version instead of just an exact `X.Y.Z` version.
+
 ## [0.28.0] - 2024-01-07
 
 [0.28.0]: https://github.com/bazelbuild/rules_python/releases/tag/0.28.0
@@ -234,8 +238,6 @@ 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.
 
-[0.27.0]: https://github.com/bazelbuild/rules_python/releases/tag/0.27.0
-
 ## [0.26.0] - 2023-10-06
 
 ### Changed

python/config_settings/BUILD.bazel

@@ -10,4 +10,7 @@ filegroup(
     visibility = ["//python:__pkg__"],
 )
 
-construct_config_settings(python_versions = TOOL_VERSIONS.keys())
+construct_config_settings(
+    name = "construct_config_settings",
+    python_versions = TOOL_VERSIONS.keys(),
+)

python/config_settings/config_settings.bzl

@@ -15,26 +15,69 @@
 """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(name, python_versions):
     """Constructs a set of configs for all Python versions.
 
     Args:
-        python_versions: The Python versions supported by rules_python.
+        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.
     """
+
+    # 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)
+
     string_flag(
         name = "python_version",
+        # TODO: The default here should somehow match the MODULE config
         build_setting_default = python_versions[0],
-        values = python_versions,
+        values = sorted(allowed_flag_values),
         visibility = ["//visibility:public"],
     )
 
-    for python_version in python_versions:
-        python_version_constraint_setting = "is_python_" + python_version
+    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 = python_version_constraint_setting,
-            flag_values = {":python_version": python_version},
+            name = equals_minor_version_name,
+            flag_values = {":python_version": minor_version},
+        )
+
+        matches_minor_version_names = [equals_minor_version_name]
+
+        for micro_version in micro_versions:
+            is_micro_version_name = "is_python_" + 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)
+
+        # 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,
+        )
+
+        native.alias(
+            name = "is_python_" + minor_version,
+            actual = "_is_python_" + minor_version,
             visibility = ["//visibility:public"],
         )

tests/config_settings/BUILD.bazel

@@ -0,0 +1,19 @@
+# Copyright 2022 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+load(":construct_config_settings_tests.bzl", "construct_config_settings_test_suite")
+
+construct_config_settings_test_suite(
+    name = "construct_config_settings_tests",
+)

tests/config_settings/construct_config_settings_tests.bzl

@@ -0,0 +1,81 @@
+# Copyright 2024 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Tests for construction of Python version matching config settings."""
+
+load("@rules_testing//lib:analysis_test.bzl", "analysis_test")
+load("@rules_testing//lib:test_suite.bzl", "test_suite")
+load("@rules_testing//lib:truth.bzl", "subjects")
+load("@rules_testing//lib:util.bzl", rt_util = "util")
+
+_tests = []
+
+def _subject_impl(ctx):
+    _ = ctx  # @unused
+    return [DefaultInfo()]
+
+_subject = rule(
+    implementation = _subject_impl,
+    attrs = {
+        "match_micro": attr.string(),
+        "match_minor": attr.string(),
+        "no_match": attr.string(),
+    },
+)
+
+def _test_minor_version_matching(name):
+    rt_util.helper_target(
+        _subject,
+        name = name + "_subject",
+        match_minor = select({
+            "//python/config_settings:is_python_3.11": "matched-3.11",
+            "//conditions:default": "matched-default",
+        }),
+        match_micro = select({
+            "//python/config_settings:is_python_3.11": "matched-3.11",
+            "//conditions:default": "matched-default",
+        }),
+        no_match = select({
+            "//python/config_settings:is_python_3.12": "matched-3.12",
+            "//conditions:default": "matched-default",
+        }),
+    )
+
+    analysis_test(
+        name = name,
+        target = name + "_subject",
+        impl = _test_minor_version_matching_impl,
+        config_settings = {
+            str(Label("//python/config_settings:python_version")): "3.11.1",
+        },
+    )
+
+def _test_minor_version_matching_impl(env, target):
+    target = env.expect.that_target(target)
+    target.attr("match_minor", factory = subjects.str).equals(
+        "matched-3.11",
+    )
+    target.attr("match_micro", factory = subjects.str).equals(
+        "matched-3.11",
+    )
+    target.attr("no_match", factory = subjects.str).equals(
+        "matched-default",
+    )
+
+_tests.append(_test_minor_version_matching)
+
+def construct_config_settings_test_suite(name):
+    test_suite(
+        name = name,
+        tests = _tests,
+    )