chore: enable pipstar for experimental_index_url users (#3428)

`bazel query` may break if users right now rely on the behaviour of:

> only host platform packages are present in the whl_library instances

When we enabled `pipstar` by default, one of our user reported this
breakage
because:
1. The `triton` dependency is only used on `linux` and it is in one of
the
   `requirements` files.
2. On mac, this dependency did not have a `whl_library` repository
materialized
   and the bazel query failed because of this reason.

Hence we enable `pipstar` in a different way - we only enable it when
whl files
are downloaded via the bazel downloader and `bazel query` is less likely
to fail
if you can use the bazel downloader for all of your deps.

Work towards #2949

---------

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

Author: aignas

CHANGELOG.md

@@ -72,6 +72,9 @@ END_UNRELEASED_TEMPLATE
 ### Changed
 * (toolchains) Use toolchains from the [20251031] release.
 * (gazelle) Internally split modules mapping generation to be per-wheel for concurrency and caching.
+* (pip) `pipstar` has been enabled for all `whl_library` instances where the whl
+  is passed through a label or downloaded using the bazel downloader
+  ([#2949](https://github.com/bazel-contrib/rules_python/issues/2949)).
 
 {#v0-0-0-fixed}
 ### Fixed

python/private/pypi/hub_builder.bzl

@@ -146,6 +146,7 @@ def _pip_parse(self, module_ctx, pip_attr):
         self,
         module_ctx,
         pip_attr = pip_attr,
+        enable_pipstar = self._config.enable_pipstar or self._get_index_urls.get(pip_attr.python_version),
     )
 
 ### end of PUBLIC methods
@@ -188,7 +189,7 @@ def _add_extra_aliases(self, extra_hub_aliases):
             {alias: True for alias in aliases},
         )
 
-def _add_whl_library(self, *, python_version, whl, repo):
+def _add_whl_library(self, *, python_version, whl, repo, enable_pipstar):
     if repo == None:
         # NOTE @aignas 2025-07-07: we guard against an edge-case where there
         # are more platforms defined than there are wheels for and users
@@ -208,7 +209,7 @@ def _add_whl_library(self, *, python_version, whl, repo):
         ))
     self._whl_libraries[repo_name] = repo.args
 
-    if not self._config.enable_pipstar and "experimental_target_platforms" in repo.args:
+    if not enable_pipstar and "experimental_target_platforms" in repo.args:
         self._whl_libraries[repo_name] |= {
             "experimental_target_platforms": sorted({
                 # TODO @aignas 2025-07-07: this should be solved in a better way
@@ -342,11 +343,11 @@ def _platforms(*, python_version, config):
         )
     return platforms
 
-def _evaluate_markers(self, pip_attr):
+def _evaluate_markers(self, pip_attr, enable_pipstar):
     if self._evaluate_markers_fn:
         return self._evaluate_markers_fn
 
-    if self._config.enable_pipstar:
+    if enable_pipstar:
         return lambda _, requirements: evaluate_markers_star(
             requirements = requirements,
             platforms = self._platforms[pip_attr.python_version],
@@ -387,13 +388,15 @@ def _create_whl_repos(
         self,
         module_ctx,
         *,
-        pip_attr):
+        pip_attr,
+        enable_pipstar = False):
     """create all of the whl repositories
 
     Args:
         self: the builder.
         module_ctx: {type}`module_ctx`.
         pip_attr: {type}`struct` - the struct that comes from the tag class iteration.
+        enable_pipstar: {type}`bool` - enable the pipstar or not.
     """
     logger = self._logger
     platforms = self._platforms[pip_attr.python_version]
@@ -416,7 +419,7 @@ def _create_whl_repos(
         platforms = platforms,
         extra_pip_args = pip_attr.extra_pip_args,
         get_index_urls = self._get_index_urls.get(pip_attr.python_version),
-        evaluate_markers = _evaluate_markers(self, pip_attr),
+        evaluate_markers = _evaluate_markers(self, pip_attr, enable_pipstar),
         logger = logger,
     )
 
@@ -435,6 +438,7 @@ def _create_whl_repos(
         self,
         module_ctx,
         pip_attr = pip_attr,
+        enable_pipstar = enable_pipstar,
     )
     for whl in requirements_by_platform:
         whl_library_args = common_args | _whl_library_args(
@@ -452,16 +456,17 @@ def _create_whl_repos(
                 auth_patterns = self._config.auth_patterns or pip_attr.auth_patterns,
                 python_version = _major_minor_version(pip_attr.python_version),
                 is_multiple_versions = whl.is_multiple_versions,
-                enable_pipstar = self._config.enable_pipstar,
+                enable_pipstar = enable_pipstar,
             )
             _add_whl_library(
                 self,
                 python_version = pip_attr.python_version,
                 whl = whl,
                 repo = repo,
+                enable_pipstar = enable_pipstar,
             )
 
-def _common_args(self, module_ctx, *, pip_attr):
+def _common_args(self, module_ctx, *, pip_attr, enable_pipstar):
     interpreter = _detect_interpreter(self, pip_attr)
 
     # Construct args separately so that the lock file can be smaller and does not include unused
@@ -481,7 +486,7 @@ def _common_args(self, module_ctx, *, pip_attr):
         python_interpreter = interpreter.path,
         python_interpreter_target = interpreter.target,
     )
-    if not self._config.enable_pipstar:
+    if not enable_pipstar:
         maybe_args["experimental_target_platforms"] = pip_attr.experimental_target_platforms
 
     whl_library_args.update({k: v for k, v in maybe_args.items() if v})

python/private/pypi/whl_library.bzl

@@ -324,6 +324,8 @@ def _whl_library_impl(rctx):
 
     args = _parse_optional_attrs(rctx, args, extra_pip_args)
 
+    # also enable pipstar for any whls that are downloaded without `pip`
+    enable_pipstar = (rp_config.enable_pipstar or whl_path) and rctx.attr.config_load
     if not whl_path:
         if rctx.attr.urls:
             op_tmpl = "whl_library.BuildWheelFromSource({name}, {requirement})"
@@ -374,7 +376,7 @@ def _whl_library_impl(rctx):
     # disable pipstar for that particular case.
     #
     # Remove non-pipstar and config_load check when we release rules_python 2.
-    if rp_config.enable_pipstar and rctx.attr.config_load:
+    if enable_pipstar:
         pypi_repo_utils.execute_checked(
             rctx,
             op = "whl_library.ExtractWheel({}, {})".format(rctx.attr.name, whl_path),