feat: freethreaded support for the builder API

CHANGELOG.md

@@ -82,6 +82,8 @@ END_UNRELEASED_TEMPLATE
 * (toolchains) `local_runtime_repo` now checks if the include directory exists
   before attempting to watch it, fixing issues on macOS with system Python
   ({gh-issue}`3043`).
+* (pypi) The pipstar `defaults` configuration now supports any custom platform
+  name.
 
 {#v0-0-0-added}
 ### Added

MODULE.bazel

@@ -60,9 +60,121 @@ register_toolchains("@pythons_hub//:all")
 # Install twine for our own runfiles wheel publishing and allow bzlmod users to use it.
 
 pip = use_extension("//python/extensions:pip.bzl", "pip")
+
+# NOTE @aignas 2025-07-06: we define these platforms to keep backwards compatibility with the
+# current `experimental_index_url` implementation. Whilst we stabilize the API this list may be
+# updated with a mention in the CHANGELOG.
+[
+    pip.default(
+        arch_name = cpu,
+        config_settings = [
+            "@platforms//cpu:{}".format(cpu),
+            "@platforms//os:linux",
+            "//python/config_settings:_is_py_freethreaded_{}".format(
+                "yes" if freethreaded else "no",
+            ),
+        ],
+        env = {"platform_version": "0"},
+        marker = "python_version ~= \"3.13\"" if freethreaded else "",
+        os_name = "linux",
+        platform = "linux_{}{}".format(cpu, freethreaded),
+        platform_tags = [
+            "linux_*_{}".format(cpu),
+            "manylinux_*_{}".format(cpu),
+        ],
+        want_abis = [
+            "cp{0}{1}t",
+            "none",
+        ] if freethreaded else [],
+    )
+    for cpu in [
+        "x86_64",
+        "aarch64",
+        # TODO @aignas 2025-05-19: only leave tier 0-1 cpus when stabilizing the
+        # `pip.default` extension. i.e. drop the below values - users will have to
+        # define themselves if they need them.
+        "arm",
+        "ppc",
+        "s390x",
+    ]
+    for freethreaded in [
+        "",
+        "_freethreaded",
+    ]
+]
+
+[
+    pip.default(
+        arch_name = cpu,
+        config_settings = [
+            "@platforms//cpu:{}".format(cpu),
+            "@platforms//os:osx",
+            "//python/config_settings:_is_py_freethreaded_{}".format(
+                "yes" if freethreaded else "no",
+            ),
+        ],
+        # We choose the oldest non-EOL version at the time when we release `rules_python`.
+        # See https://endoflife.date/macos
+        env = {"platform_version": "14.0"},
+        marker = "python_version ~= \"3.13\"" if freethreaded else "",
+        os_name = "osx",
+        platform = "osx_{}{}".format(cpu, freethreaded),
+        platform_tags = [
+            "macosx_*_{}".format(suffix)
+            for suffix in platform_tag_cpus
+        ],
+        want_abis = [
+            "cp{0}{1}t",
+            "none",
+        ] if freethreaded else [],
+    )
+    for cpu, platform_tag_cpus in {
+        "aarch64": [
+            "universal2",
+            "arm64",
+        ],
+        "x86_64": [
+            "universal2",
+            "x86_64",
+        ],
+    }.items()
+    for freethreaded in [
+        "",
+        "_freethreaded",
+    ]
+]
+
+[
+    pip.default(
+        arch_name = "x86_64",
+        config_settings = [
+            "@platforms//cpu:x86_64",
+            "@platforms//os:windows",
+            "//python/config_settings:_is_py_freethreaded_{}".format(
+                "yes" if freethreaded else "no",
+            ),
+        ],
+        env = {"platform_version": "0"},
+        marker = "python_version ~= \"3.13\"" if freethreaded else "",
+        os_name = "windows",
+        platform = "windows_x86_64{}".format(freethreaded),
+        platform_tags = ["win_amd64"],
+        want_abis = [
+            "cp{0}{1}t",
+            "none",
+        ] if freethreaded else [],
+    )
+    for freethreaded in [
+        "",
+        "_freethreaded",
+    ]
+]
+
 pip.parse(
     # NOTE @aignas 2024-10-26: We have an integration test that depends on us
     # being able to build sdists for this hub, so explicitly set this to False.
+    #
+    # how do we test sdists? Maybe just worth adding a single sdist somewhere?
     download_only = False,
     experimental_index_url = "https://pypi.org/simple",
     hub_name = "rules_python_publish_deps",
@@ -155,22 +267,19 @@ dev_pip = use_extension(
     dev_dependency = True,
 )
 dev_pip.parse(
-    download_only = True,
     experimental_index_url = "https://pypi.org/simple",
     hub_name = "dev_pip",
     parallel_download = False,
     python_version = "3.11",
     requirements_lock = "//docs:requirements.txt",
 )
 dev_pip.parse(
-    download_only = True,
     experimental_index_url = "https://pypi.org/simple",
     hub_name = "dev_pip",
     python_version = "3.13",
     requirements_lock = "//docs:requirements.txt",
 )
 dev_pip.parse(
-    download_only = True,
     experimental_index_url = "https://pypi.org/simple",
     hub_name = "pypiserver",
     python_version = "3.11",

examples/bzlmod/MODULE.bazel

@@ -158,6 +158,23 @@ pip.whl_mods(
 )
 use_repo(pip, "whl_mods_hub")
 
+# Because below we are using `windows_aarch64` platform, we have to define various
+# properties for it.
+pip.default(
+    arch_name = "aarch64",
+    config_settings = [
+        "@platforms//os:windows",
+        "@platforms//cpu:aarch64",
+    ],
+    env = {
+        "platform_version": "0",
+    },
+    os_name = "windows",
+    platform = "windows_aarch64",
+    platform_tags = ["win_amd64"],
+    want_abis = [],  # default to all ABIs
+)
+
 # To fetch pip dependencies, use pip.parse. We can pass in various options,
 # but typically we pass requirements and the Python version. The Python
 # version must have been configured by a corresponding `python.toolchain()`

python/private/pypi/BUILD.bazel

@@ -120,7 +120,6 @@ bzl_library(
         ":whl_config_setting_bzl",
         ":whl_library_bzl",
         ":whl_repo_name_bzl",
-        ":whl_target_platforms_bzl",
         "//python/private:full_version_bzl",
         "//python/private:normalize_name_bzl",
         "//python/private:version_bzl",
@@ -209,7 +208,7 @@ bzl_library(
         ":parse_requirements_txt_bzl",
         ":pypi_repo_utils_bzl",
         ":requirements_files_by_platform_bzl",
-        ":whl_target_platforms_bzl",
+        ":select_whl_bzl",
         "//python/private:normalize_name_bzl",
         "//python/private:repo_utils_bzl",
     ],
@@ -252,10 +251,6 @@ bzl_library(
 bzl_library(
     name = "pep508_env_bzl",
     srcs = ["pep508_env.bzl"],
-    deps = [
-        ":pep508_platform_bzl",
-        "//python/private:version_bzl",
-    ],
 )
 
 bzl_library(
@@ -363,6 +358,15 @@ bzl_library(
     ],
 )
 
+bzl_library(
+    name = "select_whl_bzl",
+    srcs = ["select_whl.bzl"],
+    deps = [
+        ":parse_whl_name_bzl",
+        "//python/private:version_bzl",
+    ],
+)
+
 bzl_library(
     name = "simpleapi_download_bzl",
     srcs = ["simpleapi_download.bzl"],
@@ -426,5 +430,4 @@ bzl_library(
 bzl_library(
     name = "whl_target_platforms_bzl",
     srcs = ["whl_target_platforms.bzl"],
-    deps = [":parse_whl_name_bzl"],
 )

python/private/pypi/evaluate_markers.bzl

@@ -43,11 +43,11 @@ def evaluate_markers(*, requirements, platforms):
     for req_string, platform_strings in requirements.items():
         req = requirement(req_string)
         for platform_str in platform_strings:
-            env = platforms.get(platform_str)
-            if not env:
-                fail("Please define platform: '{}'".format(platform_str))
+            plat = platforms.get(platform_str)
+            if not plat:
+                continue
 
-            if evaluate(req.marker, env = env):
+            if evaluate(req.marker, env = plat.env):
                 ret.setdefault(req_string, []).append(platform_str)
 
     return ret
@@ -57,7 +57,7 @@ def evaluate_markers_py(mrctx, *, requirements, python_interpreter, python_inter
 
     Args:
         mrctx: repository_ctx or module_ctx.
-        requirements: list[str] of the requirement file lines to evaluate.
+        requirements: {type}`dict[str, list[str]]` of the requirement file lines to evaluate.
         python_interpreter: str, path to the python_interpreter to use to
             evaluate the env markers in the given requirements files. It will
             be only called if the requirements files have env markers. This