fix(bzlmod): generate config_setting values for all python toolchains (#2350)

PR #2253 broke how the config settings are generated and only generated the
config
setting values for the python version values that we would have the
registered
toolchains for. This PR restores the previous behaviour. However, if the
root
module uses `python.override` to remove the allowed toolchains, then
`config_settings` will be also affected.

(cherry picked from commit 9340a81)

Conflicts:
- CHANGELOG.md

Author: aignas

CHANGELOG.md

@@ -20,8 +20,11 @@ A brief description of the categories of changes:
 * Particular sub-systems are identified using parentheses, e.g. `(bzlmod)` or
   `(docs)`.
 
+{#v0-0-0}
 ## Unreleased
 
+[0.0.0]: https://github.com/bazelbuild/rules_python/releases/tag/0.0.0
+
 ### Changed
 - Nothing yet
 
@@ -34,6 +37,17 @@ A brief description of the categories of changes:
 ### Removed
 - Nothing yet
 
+{#v0-37-2}
+## [0.37.2] - 2024-10-27
+
+[0.37.2]: https://github.com/bazelbuild/rules_python/releases/tag/0.37.2
+
+{#v0-37-2-fixed}
+### Fixed
+* (bzlmod) Generate `config_setting` values for all available toolchains instead
+  of only the registered toolchains, which restores the previous behaviour that
+  `bzlmod` users would have observed.
+
 {#v0-37-1}
 ## [0.37.1] - 2024-10-22
 

examples/multi_python_versions/MODULE.bazel

@@ -30,6 +30,7 @@ python.toolchain(
 )
 use_repo(
     python,
+    "pythons_hub",
     python = "python_versions",
 )
 

examples/multi_python_versions/tests/BUILD.bazel

@@ -1,9 +1,14 @@
 load("@bazel_skylib//rules:copy_file.bzl", "copy_file")
+load("@bazel_skylib//rules:diff_test.bzl", "diff_test")
+load("@bazel_skylib//rules:write_file.bzl", "write_file")
 load("@python//3.10:defs.bzl", py_binary_3_10 = "py_binary", py_test_3_10 = "py_test")
 load("@python//3.11:defs.bzl", py_binary_3_11 = "py_binary", py_test_3_11 = "py_test")
 load("@python//3.8:defs.bzl", py_binary_3_8 = "py_binary", py_test_3_8 = "py_test")
 load("@python//3.9:defs.bzl", py_binary_3_9 = "py_binary", py_test_3_9 = "py_test")
+load("@pythons_hub//:versions.bzl", "MINOR_MAPPING", "PYTHON_VERSIONS")
 load("@rules_python//python:defs.bzl", "py_binary", "py_test")
+load("@rules_python//python:versions.bzl", DEFAULT_MINOR_MAPPING = "MINOR_MAPPING", DEFAULT_TOOL_VERSIONS = "TOOL_VERSIONS")
+load("@rules_python//python/private:text_util.bzl", "render")  # buildifier: disable=bzl-visibility
 load("@rules_shell//shell:sh_test.bzl", "sh_test")
 
 copy_file(
@@ -183,3 +188,37 @@ sh_test(
         "VERSION_PY_BINARY": "$(rootpath :version_3_10)",
     },
 )
+
+# The following test ensures that default toolchain versions are the same as in
+# the TOOL_VERSIONS array.
+
+# NOTE @aignas 2024-10-26: This test here is to do a sanity check and not
+# include extra dependencies - if rules_testing is included here, we can
+# potentially uses `rules_testing` for a more lightweight test.
+write_file(
+    name = "default_python_versions",
+    out = "default_python_versions.txt",
+    content = [
+        "MINOR_MAPPING:",
+        render.dict(dict(sorted(DEFAULT_MINOR_MAPPING.items()))),
+        "PYTHON_VERSIONS:",
+        render.list(sorted(DEFAULT_TOOL_VERSIONS)),
+    ],
+)
+
+write_file(
+    name = "pythons_hub_versions",
+    out = "pythons_hub_versions.txt",
+    content = [
+        "MINOR_MAPPING:",
+        render.dict(dict(sorted(MINOR_MAPPING.items()))),
+        "PYTHON_VERSIONS:",
+        render.list(sorted(PYTHON_VERSIONS)),
+    ],
+)
+
+diff_test(
+    name = "test_versions",
+    file1 = "default_python_versions",
+    file2 = "pythons_hub_versions",
+)

python/private/python.bzl

@@ -241,6 +241,7 @@ def _python_impl(module_ctx):
         # Last toolchain is default
         default_python_version = py.default_python_version,
         minor_mapping = py.config.minor_mapping,
+        python_versions = list(py.config.default["tool_versions"].keys()),
         toolchain_prefixes = [
             render.toolchain_prefix(index, toolchain.name, _TOOLCHAIN_INDEX_PAD_LENGTH)
             for index, toolchain in enumerate(py.toolchains)