fix(lint): read the base layer allowlist at the merge base

make lint and the pre-commit hook pass the base branch tip, so an allowlist entry removed on main after this branch split off was reported as newly added. The checker now resolves the merge base itself with the same helper the other gates use

scripts/check_layer_imports.py

@@ -1,6 +1,5 @@
 import argparse
 import ast
-import subprocess
 import sys
 from collections.abc import Callable, Iterable, Iterator, Sequence
 from dataclasses import dataclass
@@ -9,6 +8,8 @@ from pathlib import Path
 from types import MappingProxyType
 from typing import Final, Literal
 
+from lint_base_counts import REPO_GIT, Git, resolve_base_point
+
 PACKAGE_ROOT: Final = Path("litellm")
 ALLOWLIST: Final = Path("scripts/layer_imports_allowlist.txt")
 LEAF_MODULES: Final = frozenset(
@@ -172,11 +173,10 @@ def report(
     return new + stale + added
 
 
-def git_base_allowlist(ref: str) -> frozenset[str] | None:
-    shown: Final = subprocess.run(
-        ["git", "show", f"{ref}:{ALLOWLIST.as_posix()}"], capture_output=True, text=True, check=False
-    )
-    return parse_allowlist(shown.stdout) if shown.returncode == 0 else None
+def git_base_allowlist(ref: str, git: Git = REPO_GIT) -> frozenset[str] | None:
+    base_point: Final = resolve_base_point(ref, git)
+    tracked: Final = git(["ls-tree", "--name-only", base_point, "--", ALLOWLIST.as_posix()]).strip()
+    return parse_allowlist(git(["show", f"{base_point}:{ALLOWLIST.as_posix()}"])) if tracked else None
 
 
 class Arguments(argparse.Namespace):
@@ -189,7 +189,7 @@ def main(
 ) -> int:
     parser: Final = argparse.ArgumentParser(description="Check SDK/proxy layer import rules")
     parser.add_argument(
-        "--base", help="Also reject allowlist entries missing from the allowlist at this ref (CI passes the merge base)"
+        "--base", help="Also reject allowlist entries missing from the allowlist at the merge base with this ref"
     )
     args: Final = parser.parse_args(argv, namespace=Arguments())
     paths: Final = tuple(sorted(PACKAGE_ROOT.rglob("*.py")))

tests/unit/test_check_layer_imports.py

@@ -2,7 +2,7 @@ from pathlib import Path
 
 import pytest
 
-from scripts.check_layer_imports import main
+from scripts.check_layer_imports import git_base_allowlist, main
 
 
 def build_tree(root: Path, files: dict[str, str], allowlist: str = "") -> None:
@@ -194,3 +194,24 @@ def test_missing_base_allowlist_skips_growth_check(
     )
 
     assert run_check(tmp_path, monkeypatch, capsys, None) == (0, "")
+
+
+def test_base_allowlist_is_read_at_the_merge_base_not_the_branch_tip() -> None:
+    allowlist = "scripts/layer_imports_allowlist.txt"
+    outputs = {
+        ("merge-base", "origin/main", "HEAD"): "forkpoint\n",
+        ("ls-tree", "--name-only", "forkpoint", "--", allowlist): f"{allowlist}\n",
+        ("show", f"forkpoint:{allowlist}"): "L3 module litellm/types/foo.py litellm.router\n",
+        ("ls-tree", "--name-only", "origin/main", "--", allowlist): f"{allowlist}\n",
+        ("show", f"origin/main:{allowlist}"): "",
+    }
+
+    assert git_base_allowlist("origin/main", lambda args: outputs.get(tuple(args), "")) == frozenset(
+        {"L3 module litellm/types/foo.py litellm.router"}
+    )
+
+
+def test_base_without_an_allowlist_skips_the_growth_check() -> None:
+    outputs = {("merge-base", "origin/main", "HEAD"): "forkpoint\n"}
+
+    assert git_base_allowlist("origin/main", lambda args: outputs.get(tuple(args), "")) is None