fix: don't materialize rules_python under the remote repo contents cache

.gitattributes

@@ -1,7 +1,6 @@
 python/features.bzl export-subst
 tools/publish/*.txt linguist-generated=true
 tests/uv/lock/testdata/requirements.txt text eol=lf
-python/private/runtimes_manifest_workspace.bzl text eol=lf
-python/private/runtimes_manifest.txt text eol=lf
+python/private/runtimes_manifest.bzl text eol=lf
 
 *.bat text eol=crlf

.pre-commit-config.yaml

@@ -52,13 +52,7 @@ repos:
         name: Sort runtimes manifest
         language: system
         entry: ./python/private/tools/sort_manifest.py
-        files: ^python/private/runtimes_manifest\.txt$
-      - id: sync-runtimes-manifest
-        name: Sync runtimes manifest workspace
-        language: system
-        entry: ./python/private/tools/sync_runtimes_manifest_workspace.py
-        files: ^python/private/runtimes_manifest\.txt$
-        pass_filenames: false
+        files: ^python/private/runtimes_manifest\.bzl$
       - id: sync-downloader-configs
         name: Sync downloader configs
         language: system

news/4294.fixed.md

@@ -0,0 +1,4 @@
+(toolchains) Evaluating the {obj}`python` module extension and `@pythons_hub`
+repository no longer materializes the `@rules_python` repository when using
+`--experimental_remote_repo_contents_cache`
+([#4294](https://github.com/bazel-contrib/rules_python/issues/4294)).

python/BUILD.bazel

@@ -434,7 +434,7 @@ bzl_library(
     deps = [
         "//python/private:pbs_manifest",
         "//python/private:platform_info",
-        "//python/private:runtimes_manifest_workspace",
+        "//python/private:runtimes_manifest",
     ],
 )
 

python/private/BUILD.bazel

@@ -35,8 +35,7 @@ licenses(["notice"])
 
 exports_files([
     "runtime_env_toolchain_interpreter.sh",
-    "runtimes_manifest.txt",
-    "runtimes_manifest_workspace.bzl",
+    "runtimes_manifest.bzl",
 ])
 
 distribution_filegroup(
@@ -224,10 +223,13 @@ sentinel(
     visibility = ["//visibility:public"],
 )
 
-py_binary(
-    name = "sync_runtimes_manifest_workspace",
-    srcs = ["tools/sync_runtimes_manifest_workspace.py"],
-    visibility = ["//:__subpackages__"],
+py_library(
+    name = "sort_manifest_lib",
+    srcs = ["tools/sort_manifest.py"],
+    imports = ["../.."],
+    visibility = [
+        "//tests/toolchains:__pkg__",
+    ],
 )
 
 # Tool used by py_test's validation action to statically check that the main
@@ -749,6 +751,7 @@ bzl_library(
         ":python_register_toolchains",
         ":pythons_hub",
         ":repo_utils",
+        ":runtimes_manifest",
         ":toolchains_repo",
         ":version",
         "//python:versions",
@@ -796,6 +799,7 @@ bzl_library(
     srcs = ["pythons_hub.bzl"],
     deps = [
         ":pbs_manifest",
+        ":runtimes_manifest",
         ":text_util",
         ":toolchains_repo",
         "//python:versions",
@@ -1012,8 +1016,8 @@ bzl_library(
 )
 
 bzl_library(
-    name = "runtimes_manifest_workspace",
-    srcs = ["runtimes_manifest_workspace.bzl"],
+    name = "runtimes_manifest",
+    srcs = ["runtimes_manifest.bzl"],
 )
 
 bzl_library(

python/private/python.bzl

@@ -30,6 +30,7 @@ load(":pyproject_utils.bzl", "read_pyproject", "version_from_requires_python")
 load(":python_register_toolchains.bzl", "python_register_toolchains")
 load(":pythons_hub.bzl", "hub_repo")
 load(":repo_utils.bzl", "repo_utils")
+load(":runtimes_manifest.bzl", "MANIFEST_TEXT")
 load(
     ":toolchains_repo.bzl",
     "host_compatible_python_repo",
@@ -39,13 +40,20 @@ load(
 )
 load(":version.bzl", "version")
 
-def parse_modules(*, module_ctx, logger = None, _fail = fail):
+def parse_modules(
+        *,
+        module_ctx,
+        logger = None,
+        _fail = fail,
+        _default_runtime_manifest = MANIFEST_TEXT):
     """Parse the modules and return a struct for registrations.
 
     Args:
         module_ctx: {type}`module_ctx` module context.
         logger: {type}`repo_utils.logger` A logger to use.
         _fail: {type}`function` the failure function, mainly for testing.
+        _default_runtime_manifest: {type}`str` the built-in runtimes manifest,
+            only overridden for testing.
 
     Returns:
         A struct with the following attributes:
@@ -84,7 +92,12 @@ def parse_modules(*, module_ctx, logger = None, _fail = fail):
     # Map of string Major.Minor or Major.Minor.Patch to the toolchain_info struct
     global_toolchain_versions = {}
 
-    config = _get_toolchain_config(mctx = module_ctx, modules = module_ctx.modules, _fail = _fail)
+    config = _get_toolchain_config(
+        mctx = module_ctx,
+        modules = module_ctx.modules,
+        default_runtime_manifest = _default_runtime_manifest,
+        _fail = _fail,
+    )
 
     default_python_version = _compute_default_python_version(module_ctx)
 
@@ -762,11 +775,12 @@ def _populate_from_pbs_manifest(
         mctx,
         add_runtime_manifest_urls = [],
         add_runtime_manifest_files = [],
+        add_runtime_manifest_contents = [],
         runtime_manifest_sha = "",
         base_urls = [],
         available_versions,
         _fail):
-    manifest_contents = []
+    manifest_contents = list(add_runtime_manifest_contents)
 
     if add_runtime_manifest_urls:
         manifest_path = mctx.path("runtime_manifest")
@@ -835,12 +849,19 @@ def _populate_from_pbs_manifest(
             v_dict.setdefault("url", {})[platform_key] = urls
             v_dict.setdefault("strip_prefix", {})[platform_key] = strip_prefix
 
-def _get_toolchain_config(*, mctx, modules, _fail = fail):
+def _get_toolchain_config(
+        *,
+        mctx,
+        modules,
+        default_runtime_manifest,
+        _fail = fail):
     """Computes the configs for toolchains.
 
     Args:
         mctx: The module context.
         modules: The modules from module_ctx
+        default_runtime_manifest: The contents of the built-in runtimes
+            manifest.
         _fail: Function to call for failing; only used for testing.
 
     Returns:
@@ -864,7 +885,9 @@ def _get_toolchain_config(*, mctx, modules, _fail = fail):
 
     _populate_from_pbs_manifest(
         mctx = mctx,
-        add_runtime_manifest_files = [Label("//python/private:runtimes_manifest.txt")],
+        # Loaded rather than read by Label, so the remote repo contents cache
+        # does not have to materialize this repo.
+        add_runtime_manifest_contents = [default_runtime_manifest],
         base_urls = DEFAULT_RELEASE_BASE_URLS,
         available_versions = available_versions,
         _fail = _fail,

python/private/pythons_hub.bzl

@@ -16,6 +16,7 @@
 
 load("//python:versions.bzl", "PLATFORMS")
 load(":pbs_manifest.bzl", "parse_runtime_manifest")
+load(":runtimes_manifest.bzl", "MANIFEST_TEXT")
 load(":text_util.bzl", "render")
 load(":toolchains_repo.bzl", "toolchain_suites_content")
 
@@ -121,8 +122,9 @@ def _hub_repo_impl(rctx):
 
     python_versions = rctx.attr.python_versions
     if not python_versions and not rctx.attr.toolchain_python_versions:
-        content = rctx.read(rctx.path(Label("//python/private:runtimes_manifest.txt")))
-        entries = parse_runtime_manifest(content)
+        # Loaded rather than read by Label, so the remote repo contents cache
+        # does not have to materialize this repo.
+        entries = parse_runtime_manifest(MANIFEST_TEXT)
         python_versions_str = render.list(sorted({getattr(e, "python_version", ""): None for e in entries if getattr(e, "python_version", "")}))
 
     else:

python/private/runtimes_manifest.txt → python/private/runtimes_manifest.bzl

@@ -1,6 +1,16 @@
+"""Manifest of built-in Python runtimes.
+
+It's a .bzl file so that both WORKSPACE mode and Bzlmod can load the manifest
+directly without needing to read a file by Label (which would otherwise force
+Bazel's remote repository contents cache to materialize the entire repository).
+"""
+
+MANIFEST_TEXT = """
 # Manifest of runtimes to make available
-# Originally generated circa 2026-06 from the runtimes in TOOL_VERSIONS from the original python/versions.bzl
-# To sort this file, execute: ./python/private/tools/sort_manifest.py python/private/runtimes_manifest.txt
+# Originally generated circa 2026-06 from the runtimes in TOOL_VERSIONS from
+# the original python/versions.bzl
+# To sort this file, execute:
+#   ./python/private/tools/sort_manifest.py python/private/runtimes_manifest.bzl
 
 1409acd9a506e2d1d3b65c1488db4e40d8f19d09a7df099667c87a506f71c0ef  20220227/cpython-3.10.2+20220227-aarch64-apple-darwin-install_only.tar.gz
 8f351a8cc348bb45c0f95b8634c8345ec6e749e483384188ad865b7428342703  20220227/cpython-3.10.2+20220227-aarch64-unknown-linux-gnu-install_only.tar.gz
@@ -1038,3 +1048,4 @@ ceb5637723387877f65b869c3d2cc36975a689824df0d075f0f39d26afb0d2b6  20261003/cpyth
 986fda009bd9f37397f47a52d9bb37b761e7bc3d7dc0403a5702c050ee9cd091  20261003/cpython-3.15.0rc3+20261003-x86_64-unknown-linux-musl-freethreaded-install_only_stripped.tar.gz
 4a69a480e523e9ed4d5deb941a0c0ccfe1001f3269f6b3091975f059c14de99d  20261003/cpython-3.15.0rc3+20261003-x86_64-unknown-linux-musl-install_only.tar.gz
 2be25b45a6f84cc46f6f0cb144c4292dd0e5bbdb3f07442a0f270b51ecc7da0f  20261003/cpython-3.15.0rc3+20261003-x86_64-unknown-linux-musl-install_only_stripped.tar.gz
+"""