Pass around the list of loaded platforms for each toolchain

Author: aignas

examples/bzlmod/MODULE.bazel.lock

@@ -213,6 +213,7 @@ def parse_modules(*, module_ctx, _fail = fail):
 def _python_impl(module_ctx):
     py = parse_modules(module_ctx = module_ctx)
 
+    loaded_platforms = {}
     for toolchain_info in py.toolchains:
         # Ensure that we pass the full version here.
         full_python_version = full_version(
@@ -228,7 +229,7 @@ def _python_impl(module_ctx):
         kwargs.update(py.config.kwargs.get(toolchain_info.python_version, {}))
         kwargs.update(py.config.kwargs.get(full_python_version, {}))
         kwargs.update(py.config.default)
-        python_register_toolchains(
+        loaded_platforms[full_python_version] = python_register_toolchains(
             name = toolchain_info.name,
             _internal_bzlmod_toolchain_call = True,
             **kwargs
@@ -257,6 +258,7 @@ def _python_impl(module_ctx):
             for i in range(len(py.toolchains))
         ],
         toolchain_user_repository_names = [t.name for t in py.toolchains],
+        loaded_platforms = loaded_platforms,
     )
 
     # This is require in order to support multiple version py_test

python/private/python.bzl

@@ -73,6 +73,9 @@ def python_register_toolchains(
         minor_mapping: {type}`dict[str, str]` contains a mapping from `X.Y` to `X.Y.Z`
             version.
         **kwargs: passed to each {obj}`python_repository` call.
+
+    Returns:
+        on bzlmod this returns the loaded platform labels.
     """
     bzlmod_toolchain_call = kwargs.pop("_internal_bzlmod_toolchain_call", False)
     if bzlmod_toolchain_call:
@@ -168,11 +171,13 @@ def python_register_toolchains(
 
     # in bzlmod we write out our own toolchain repos
     if bzlmod_toolchain_call:
-        return
+        return loaded_platforms
 
     toolchains_repo(
         name = toolchain_repo_name,
         python_version = python_version,
         set_python_version_constraint = set_python_version_constraint,
         user_repository_name = name,
+        platforms = loaded_platforms,
     )
+    return None

python/private/python_register_toolchains.bzl

@@ -46,7 +46,8 @@ def _hub_build_file_content(
         python_versions,
         set_python_version_constraints,
         user_repository_names,
-        workspace_location):
+        workspace_location,
+        loaded_platforms):
     """This macro iterates over each of the lists and returns the toolchain content.
 
     python_toolchain_build_file_content is called to generate each of the toolchain
@@ -65,6 +66,7 @@ def _hub_build_file_content(
                 python_version = python_versions[i],
                 set_python_version_constraint = set_python_version_constraints[i],
                 user_repository_name = user_repository_names[i],
+                loaded_platforms = loaded_platforms[python_versions[i]],
             )
             for i in range(len(python_versions))
         ],
@@ -103,6 +105,7 @@ def _hub_repo_impl(rctx):
             rctx.attr.toolchain_set_python_version_constraints,
             rctx.attr.toolchain_user_repository_names,
             rctx.attr._rules_python_workspace,
+            rctx.attr.loaded_platforms,
         ),
         executable = False,
     )
@@ -149,6 +152,9 @@ This rule also writes out the various toolchains for the different Python versio
             doc = "Default Python version for the build in `X.Y` or `X.Y.Z` format.",
             mandatory = True,
         ),
+        "loaded_platforms": attr.string_list_dict(
+            doc = "The mapping from platform to version",
+        ),
         "minor_mapping": attr.string_dict(
             doc = "The minor mapping of the `X.Y` to `X.Y.Z` format that is used in config settings.",
             mandatory = True,

python/private/pythons_hub.bzl

@@ -41,7 +41,8 @@ def python_toolchain_build_file_content(
         prefix,
         python_version,
         set_python_version_constraint,
-        user_repository_name):
+        user_repository_name,
+        loaded_platforms):
     """Creates the content for toolchain definitions for a build file.
 
     Args:
@@ -51,6 +52,8 @@ def python_toolchain_build_file_content(
             have the Python version constraint added as a requirement for
             matching the toolchain, "False" if not.
         user_repository_name: names for the user repos
+        loaded_platforms: the list of platform identifiers for which to generate
+            the toolchain targets.
 
     Returns:
         build_content: Text containing toolchain definitions
@@ -78,6 +81,7 @@ py_toolchain_suite(
             python_version = python_version,
         )
         for platform, meta in PLATFORMS.items()
+        if platform in loaded_platforms
     ])
 
 def _toolchains_repo_impl(rctx):
@@ -100,6 +104,7 @@ load("@{rules_python}//python/private:py_toolchain_suite.bzl", "py_toolchain_sui
         python_version = rctx.attr.python_version,
         set_python_version_constraint = str(rctx.attr.set_python_version_constraint),
         user_repository_name = rctx.attr.user_repository_name,
+        loaded_platforms = rctx.attr.platforms,
     )
 
     rctx.file("BUILD.bazel", build_content + toolchains)
@@ -109,6 +114,7 @@ toolchains_repo = repository_rule(
     doc = "Creates a repository with toolchain definitions for all known platforms " +
           "which can be registered or selected.",
     attrs = {
+        "platforms": attr.string_list(doc = "List of platforms for which the toolchain definitions shall be created"),
         "python_version": attr.string(doc = "The Python version."),
         "set_python_version_constraint": attr.bool(doc = "if target_compatible_with for the toolchain should set the version constraint"),
         "user_repository_name": attr.string(doc = "what the user chose for the base name"),