fix(repo setup): Skip aliases for unloaded toolchains (#1473)

kilian-funk · web-flow · commit ff309353a7a1 · 2023-10-10T15:57:44.000Z
Some platforms don't contain every version, e.g. s390x doesn't have 3.8, which is indicated by a missing sha256 value. When this happens, no repository for the runtime is created (`python_repository` rule). Similar logic needs to be in the toolchains setup logic because otherwise a reference to an undefined repository exists in the select() expression of the aliases. Because those references are lazily evaluated, they don't always cause a problem, but do mean that query operations (e.g., `rdeps()`) can't work and the order of entries is important (which is surprising). Closes #1472
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -19,6 +19,12 @@ A brief description of the categories of changes:
 
 ## Unreleased
 
+### Fixed
+
+* Skip aliases for unloaded toolchains. Some Python versions that don't have full
+  platform support, and referencing their undefined repositories can break operations
+  like `bazel query rdeps(...)`.
+
 ## [0.26.0] - 2023-10-06
 
 ### Changed
diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
@@ -155,22 +155,27 @@ def _toolchain_aliases_impl(rctx):
     build_contents = """\
 # Generated by python/private/toolchains_repo.bzl
 package(default_visibility = ["//visibility:public"])
-load("@rules_python//python:versions.bzl", "PLATFORMS", "gen_python_config_settings")
+load("@rules_python//python:versions.bzl", "gen_python_config_settings")
 gen_python_config_settings()
 exports_files(["defs.bzl"])
-alias(name = "files",           actual = select({{":" + item: "@{py_repository}_" + item + "//:files" for item in PLATFORMS.keys()}}))
-alias(name = "includes",        actual = select({{":" + item: "@{py_repository}_" + item + "//:includes" for item in PLATFORMS.keys()}}))
-alias(name = "libpython",       actual = select({{":" + item: "@{py_repository}_" + item + "//:libpython" for item in PLATFORMS.keys()}}))
-alias(name = "py3_runtime",     actual = select({{":" + item: "@{py_repository}_" + item + "//:py3_runtime" for item in PLATFORMS.keys()}}))
-alias(name = "python_headers",  actual = select({{":" + item: "@{py_repository}_" + item + "//:python_headers" for item in PLATFORMS.keys()}}))
-alias(name = "python_runtimes", actual = select({{":" + item: "@{py_repository}_" + item + "//:python_runtimes" for item in PLATFORMS.keys()}}))
-alias(name = "python3",         actual = select({{":" + item: "@{py_repository}_" + item + "//:" + ("python.exe" if "windows" in item else "bin/python3") for item in PLATFORMS.keys()}}))
+
+PLATFORMS = [
+{loaded_platforms}
+]
+alias(name = "files",           actual = select({{":" + item: "@{py_repository}_" + item + "//:files" for item in PLATFORMS}}))
+alias(name = "includes",        actual = select({{":" + item: "@{py_repository}_" + item + "//:includes" for item in PLATFORMS}}))
+alias(name = "libpython",       actual = select({{":" + item: "@{py_repository}_" + item + "//:libpython" for item in PLATFORMS}}))
+alias(name = "py3_runtime",     actual = select({{":" + item: "@{py_repository}_" + item + "//:py3_runtime" for item in PLATFORMS}}))
+alias(name = "python_headers",  actual = select({{":" + item: "@{py_repository}_" + item + "//:python_headers" for item in PLATFORMS}}))
+alias(name = "python_runtimes", actual = select({{":" + item: "@{py_repository}_" + item + "//:python_runtimes" for item in PLATFORMS}}))
+alias(name = "python3",         actual = select({{":" + item: "@{py_repository}_" + item + "//:" + ("python.exe" if "windows" in item else "bin/python3") for item in PLATFORMS}}))
 """.format(
         py_repository = rctx.attr.user_repository_name,
+        loaded_platforms = "\n".join(["    \"{}\",".format(p) for p in rctx.attr.platforms]),
     )
     if not is_windows:
         build_contents += """\
-alias(name = "pip",             actual = select({{":" + item: "@{py_repository}_" + item + "//:python_runtimes" for item in PLATFORMS.keys() if "windows" not in item}}))
+alias(name = "pip",             actual = select({{":" + item: "@{py_repository}_" + item + "//:python_runtimes" for item in PLATFORMS if "windows" not in item}}))
 """.format(
             py_repository = rctx.attr.user_repository_name,
             host_platform = host_platform,
@@ -239,6 +244,9 @@ toolchain_aliases = repository_rule(
     a BUILD.bazel file declaring aliases to the host platform's targets.
     """,
     attrs = {
+        "platforms": attr.string_list(
+            doc = "List of platforms for which aliases shall be created",
+        ),
         "python_version": attr.string(doc = "The Python version."),
         "user_repository_name": attr.string(
             mandatory = True,
diff --git a/python/repositories.bzl b/python/repositories.bzl
@@ -553,11 +553,13 @@ def python_register_toolchains(
                 ))
             register_coverage_tool = False
 
+    loaded_platforms = []
     for platform in PLATFORMS.keys():
         sha256 = tool_versions[python_version]["sha256"].get(platform, None)
         if not sha256:
             continue
 
+        loaded_platforms.append(platform)
         (release_filename, urls, strip_prefix, patches) = get_release_info(platform, python_version, base_url, tool_versions)
 
         # allow passing in a tool version
@@ -604,6 +606,7 @@ def python_register_toolchains(
         name = name,
         python_version = python_version,
         user_repository_name = name,
+        platforms = loaded_platforms,
     )
 
     # in bzlmod we write out our own toolchain repos
