fix: take custom tools versions into account when selecting Python interpreter (#654)

python/repositories.bzl

diff --git a/python/repositories.bzl b/python/repositories.bzl
index 60ab918..0968326 100644
--- a/python/repositories.bzl
+++ b/python/repositories.bzl
@@ -41,8 +41,8 @@
 
     platform = rctx.attr.platform
     python_version = rctx.attr.python_version
-    base_url = rctx.attr.base_url
-    (release_filename, url) = get_release_url(platform, python_version, base_url)
+    release_filename = rctx.attr.release_filename
+    url = rctx.attr.url
 
     if release_filename.endswith(".zst"):
         rctx.download(
@@ -101,7 +101,7 @@
         if exec_result.return_code:
             fail(exec_result.stderr)
 
-    python_bin = "python.exe" if ("windows" in rctx.attr.platform) else "bin/python3"
+    python_bin = "python.exe" if ("windows" in platform) else "bin/python3"
 
     build_content = """\
 # Generated by python/repositories.bzl
@@ -155,17 +155,15 @@
         "name": rctx.attr.name,
         "platform": platform,
         "python_version": python_version,
+        "release_filename": release_filename,
         "sha256": rctx.attr.sha256,
+        "url": url,
     }
 
 python_repository = repository_rule(
     _python_repository_impl,
     doc = "Fetches the external tools needed for the Python toolchain.",
     attrs = {
-        "base_url": attr.string(
-            doc = "The base URL used for releases, will be joined to the templated 'url' field in the tool_versions dict",
-            default = DEFAULT_RELEASE_BASE_URL,
-        ),
         "distutils": attr.label(
             allow_single_file = True,
             doc = "A distutils.cfg file to be included in the Python installation. " +
@@ -187,10 +185,18 @@
             mandatory = True,
             values = TOOL_VERSIONS.keys() + MINOR_MAPPING.keys(),
         ),
+        "release_filename": attr.string(
+            doc = "The filename of the interpreter to be downloaded",
+            mandatory = True,
+        ),
         "sha256": attr.string(
             doc = "The SHA256 integrity hash for the Python interpreter tarball.",
             mandatory = True,
         ),
+        "url": attr.string(
+            doc = "The URL of the interpreter to download",
+            mandatory = True,
+        ),
         "zstd_sha256": attr.string(
             default = "7c42d56fac126929a6a85dbc73ff1db2411d04f104fae9bdea51305663a83fd0",
         ),
@@ -229,6 +235,8 @@
         in python/versions.bzl will be used
         **kwargs: passed to each python_repositories call.
     """
+    base_url = kwargs.pop("base_url", DEFAULT_RELEASE_BASE_URL)
+
     if python_version in MINOR_MAPPING:
         python_version = MINOR_MAPPING[python_version]
 
@@ -237,6 +245,8 @@
         if not sha256:
             continue
 
+        (release_filename, url) = get_release_url(platform, python_version, base_url, tool_versions)
+
         python_repository(
             name = "{name}_{platform}".format(
                 name = name,
@@ -245,6 +255,8 @@
             sha256 = sha256,
             platform = platform,
             python_version = python_version,
+            release_filename = release_filename,
+            url = url,
             distutils = distutils,
             distutils_content = distutils_content,
             **kwargs

python/versions.bzl

diff --git a/python/versions.bzl b/python/versions.bzl
index 8aaa4a0..c5445ec 100644
--- a/python/versions.bzl
+++ b/python/versions.bzl
@@ -22,15 +22,6 @@
 
 DEFAULT_RELEASE_BASE_URL = "https://github.com/indygreg/python-build-standalone/releases/download"
 
-def get_release_url(platform, python_version, base_url = DEFAULT_RELEASE_BASE_URL):
-    release_filename = TOOL_VERSIONS[python_version]["url"].format(
-        platform = platform,
-        python_version = python_version,
-        build = "static-install_only" if (WINDOWS_NAME in platform) else "install_only",
-    )
-    url = "/".join([base_url, release_filename])
-    return (release_filename, url)
-
 # When updating the versions and releases, run the following command to get
 # the hashes:
 #   bazel run //python/private:print_toolchains_checksums
@@ -47,6 +38,7 @@
     "3.8.12": {
         "url": "20220227/cpython-{python_version}+20220227-{platform}-{build}.tar.gz",
         "sha256": {
+            "aarch64-apple-darwin": "f9a3cbb81e0463d6615125964762d133387d561b226a30199f5b039b20f1d944",
             "x86_64-apple-darwin": "f323fbc558035c13a85ce2267d0fad9e89282268ecb810e364fff1d0a079d525",
             "x86_64-pc-windows-msvc": "924f9fd51ff6ccc533ed8e96c5461768da5781eb3dfc11d846f9e300fab44eda",
             "x86_64-unknown-linux-gnu": "5be9c6d61e238b90dfd94755051c0d3a2d8023ebffdb4b0fa4e8fedd09a6cab6",
@@ -116,6 +108,32 @@
     ),
 }
 
+def get_release_url(platform, python_version, base_url = DEFAULT_RELEASE_BASE_URL, tool_versions = TOOL_VERSIONS):
+    """Resolve the release URL for the requested interpreter version
+
+    Args:
+        platform: The platform string for the interpreter
+        python_version: The version of the intterpreter to get
+        base_url: The URL to prepend to the 'url' attr in the tool_versions dict
+        tool_versions: A dict listing the interpreter versions, their SHAs and URL
+
+    Returns:
+        filename and url pair
+    """
+
+    url = tool_versions[python_version]["url"]
+
+    if type(url) == type({}):
+        url = url[platform]
+
+    release_filename = url.format(
+        platform = platform,
+        python_version = python_version,
+        build = "static-install_only" if (WINDOWS_NAME in platform) else "install_only",
+    )
+    url = "/".join([base_url, release_filename])
+    return (release_filename, url)
+
 def print_toolchains_checksums(name):
     native.genrule(
         name = name,