add docs for features.bzl

Author: rickeylev

docs/BUILD.bazel

@@ -81,6 +81,7 @@ sphinx_stardocs(
     name = "bzl_api_docs",
     srcs = [
         "//python:defs_bzl",
+        "//python:features_bzl",
         "//python:packaging_bzl",
         "//python:pip_bzl",
         "//python:py_binary_bzl",

python/BUILD.bazel

@@ -79,6 +79,9 @@ bzl_library(
 bzl_library(
     name = "features_bzl",
     srcs = ["features.bzl"],
+    deps = [
+        "@rules_python_internal//:rules_python_config_bzl",
+    ],
 )
 
 bzl_library(

python/features.bzl

@@ -19,9 +19,48 @@ load("@rules_python_internal//:rules_python_config.bzl", "config")
 # See https://git-scm.com/docs/git-archive/2.29.0#Documentation/git-archive.txt-export-subst
 _VERSION_PRIVATE = "$Format:%(describe:tags=true)$"
 
+def _features_typedef():
+    """Information about features rules_python has implemented.
+
+    ::::{field} precompile
+    :type: bool
+
+    True if the precompile attributes are available.
+    :::{versionadded} TODO
+    :::
+    ::::
+
+    ::::{field} site_packages_root_attr
+    :type: bool
+
+    True if the {obj}`site_packages_root` attribute is available.
+
+    :::{versionadded} VERSION_NEXT_FEATURE
+    :::
+    ::::
+
+    ::::{field} uses_builtin_rules
+    :type: bool
+
+    True if the rules are using the Bazel-builtin implementation.
+
+    :::{versionadded} TODO
+    :::
+    ::::
+
+    ::::{field} version
+    :type: str
+
+    The rules_python version. This is a semver format, e.g. `X.Y.Z` with
+    optional trailing `-rcN`. For unreleased versions, it is an empty string.
+    :::{versionadded} TODO
+    ::::
+    """
+
 features = struct(
-    version = _VERSION_PRIVATE if "$Format" not in _VERSION_PRIVATE else "",
+    TYPEDEF = _features_typedef,
     precompile = True,
-    uses_builtin_rules = not config.enable_pystar,
     site_packages_root_attr = True,
+    uses_builtin_rules = not config.enable_pystar,
+    version = _VERSION_PRIVATE if "$Format" not in _VERSION_PRIVATE else "",
 )