fix(bzlmod pip): ensure that sub-modules do not have invalid repos (#1549)

This fixes the cases where the 'default_version' is passed to the
'render_pkg_aliases' utility but the 'default_version' is not present
for the wheels. This usually happens when a sub-module is using the
'pip.parse' extension and the default_version can only be set by the
root module.

Previously, such a case would generate a `select()` expression that
mapped
the default condition to a non-existent target (because the sub-module
didn't
call `pip.parse()` with that version). This would either result in
errors
due the target not existing, or silently using a target intended for a
different Python version (which may work, but isn't correct to so).

Now, it results in a error via `select.no_match_error`.

Fixes #1548.

Author: aignas

CHANGELOG.md

@@ -86,6 +86,10 @@ Breaking changes:
 * (gazelle) Generate a single `py_test` target when `gazelle:python_generation_mode project`
   is used.
 
+* (bzlmod) sub-modules now don't have the `//conditions:default` clause in the
+  hub repos created by `pip.parse`. This should fix confusing error messages
+  in case there is a misconfiguration of toolchains or a bug in `rules_python`.
+
 ### Added
 
 * (bzlmod) Added `.whl` patching support via `patches` and `patch_strip`

python/private/render_pkg_aliases.bzl

@@ -109,7 +109,11 @@ def _render_common_aliases(repo_name, name, versions = None, default_version = N
     if versions:
         versions = sorted(versions)
 
-    if versions and not default_version:
+    if not versions:
+        pass
+    elif default_version in versions:
+        pass
+    else:
         error_msg = NO_MATCH_ERROR_MESSAGE_TEMPLATE.format(
             supported_versions = ", ".join(versions),
             rules_python = rules_python,
@@ -119,6 +123,10 @@ def _render_common_aliases(repo_name, name, versions = None, default_version = N
             error_msg = error_msg,
         ))
 
+        # This is to simplify the code in _render_whl_library_alias and to ensure
+        # that we don't pass a 'default_version' that is not in 'versions'.
+        default_version = None
+
     lines.append(
         render.alias(
             name = name,

tests/pip_hub_repository/render_pkg_aliases/render_pkg_aliases_test.bzl

@@ -222,6 +222,93 @@ alias(
 
 _tests.append(_test_bzlmod_aliases_with_no_default_version)
 
+def _test_bzlmod_aliases_for_non_root_modules(env):
+    actual = render_pkg_aliases(
+        default_version = "3.2.4",
+        repo_name = "pypi",
+        rules_python = "rules_python",
+        whl_map = {
+            "bar-baz": ["3.2.3", "3.1.3"],
+        },
+    )
+
+    want_key = "bar_baz/BUILD.bazel"
+    want_content = """\
+package(default_visibility = ["//visibility:public"])
+
+_NO_MATCH_ERROR = \"\"\"\\
+No matching wheel for current configuration's Python version.
+
+The current build configuration's Python version doesn't match any of the Python
+versions available for this wheel. This wheel supports the following Python versions:
+    3.1.3, 3.2.3
+
+As matched by the `@rules_python//python/config_settings:is_python_<version>`
+configuration settings.
+
+To determine the current configuration's Python version, run:
+    `bazel config <config id>` (shown further below)
+and look for
+    rules_python//python/config_settings:python_version
+
+If the value is missing, then the "default" Python version is being used,
+which has a "null" version value and will not match version constraints.
+\"\"\"
+
+alias(
+    name = "bar_baz",
+    actual = ":pkg",
+)
+
+alias(
+    name = "pkg",
+    actual = select(
+        {
+            "@@rules_python//python/config_settings:is_python_3.1.3": "@pypi_31_bar_baz//:pkg",
+            "@@rules_python//python/config_settings:is_python_3.2.3": "@pypi_32_bar_baz//:pkg",
+        },
+        no_match_error = _NO_MATCH_ERROR,
+    ),
+)
+
+alias(
+    name = "whl",
+    actual = select(
+        {
+            "@@rules_python//python/config_settings:is_python_3.1.3": "@pypi_31_bar_baz//:whl",
+            "@@rules_python//python/config_settings:is_python_3.2.3": "@pypi_32_bar_baz//:whl",
+        },
+        no_match_error = _NO_MATCH_ERROR,
+    ),
+)
+
+alias(
+    name = "data",
+    actual = select(
+        {
+            "@@rules_python//python/config_settings:is_python_3.1.3": "@pypi_31_bar_baz//:data",
+            "@@rules_python//python/config_settings:is_python_3.2.3": "@pypi_32_bar_baz//:data",
+        },
+        no_match_error = _NO_MATCH_ERROR,
+    ),
+)
+
+alias(
+    name = "dist_info",
+    actual = select(
+        {
+            "@@rules_python//python/config_settings:is_python_3.1.3": "@pypi_31_bar_baz//:dist_info",
+            "@@rules_python//python/config_settings:is_python_3.2.3": "@pypi_32_bar_baz//:dist_info",
+        },
+        no_match_error = _NO_MATCH_ERROR,
+    ),
+)"""
+
+    env.expect.that_collection(actual.keys()).contains_exactly([want_key])
+    env.expect.that_str(actual[want_key]).equals(want_content)
+
+_tests.append(_test_bzlmod_aliases_for_non_root_modules)
+
 def _test_bzlmod_aliases_are_created_for_all_wheels(env):
     actual = render_pkg_aliases(
         default_version = "3.2.3",