make empty requirements file work

Author: aignas

python/private/pip_config_settings.bzl

@@ -90,7 +90,7 @@ _flags = struct(
 
 def pip_config_settings(
         *,
-        python_versions,
+        python_versions = [],
         glibc_versions = [],
         muslc_versions = [],
         osx_versions = [],

python/private/render_pkg_aliases.bzl

@@ -399,7 +399,7 @@ def multiplatform_whl_aliases(*, aliases, default_version, **kwargs):
     ret.extend(versioned.values())
     return ret
 
-def _render_pip_config_settings(python_versions, target_platforms = [], osx_versions = [], glibc_versions = [], muslc_versions = []):
+def _render_pip_config_settings(python_versions = [], target_platforms = [], osx_versions = [], glibc_versions = [], muslc_versions = []):
     return """\
 load("@rules_python//python/private:pip_config_settings.bzl", "pip_config_settings")
 

tests/pip_hub_repository/render_pkg_aliases/render_pkg_aliases_test.bzl

@@ -438,6 +438,15 @@ def _test_aliases_with_groups(env):
 
 _tests.append(_test_aliases_with_groups)
 
+def _test_empty_flag_versions(env):
+    got = get_whl_flag_versions(
+        aliases = [],
+    )
+    want = {}
+    env.expect.that_dict(got).contains_exactly(want)
+
+_tests.append(_test_empty_flag_versions)
+
 def _test_get_python_versions(env):
     got = get_whl_flag_versions(
         aliases = [
@@ -758,6 +767,7 @@ def _test_cp37_abi3_manylinux_2_17_musllinux_1_1_aarch64(env):
 _tests.append(_test_cp37_abi3_manylinux_2_17_musllinux_1_1_aarch64)
 
 def _test_multiplatform_whl_aliases_empty(env):
+    # Check that we still work with an empty requirements.txt
     got = multiplatform_whl_aliases(aliases = [], default_version = None)
     env.expect.that_collection(got).contains_exactly([])