[Build] Make sure local main branch is synced when VLLM_USE_PRECOMPILED=1 (#13921)

Signed-off-by: Cody Yu <hao.yu.cody@gmail.com>

setup.py

@@ -2,6 +2,7 @@
 
 import ctypes
 import importlib.util
+import json
 import logging
 import os
 import re
@@ -269,9 +270,32 @@ class repackage_wheel(build_ext):
     """Extracts libraries and other files from an existing wheel."""
 
     def get_base_commit_in_main_branch(self) -> str:
-        import subprocess
+        # Force to use the nightly wheel. This is mainly used for CI testing.
+        if envs.VLLM_TEST_USE_PRECOMPILED_NIGHTLY_WHEEL:
+            return "nightly"
 
         try:
+            # Get the latest commit hash of the upstream main branch.
+            resp_json = subprocess.check_output([
+                "curl", "-s",
+                "https://api.github.com/repos/vllm-project/vllm/commits/main"
+            ]).decode("utf-8")
+            upstream_main_commit = json.loads(resp_json)["sha"]
+
+            # Check if the local main branch is up-to-date. This is to ensure
+            # the base commit we found is the most recent commit on the main
+            # branch.
+            local_main_commit = subprocess.check_output(
+                ["git", "rev-parse", "main"]).decode("utf-8").strip()
+            if local_main_commit != upstream_main_commit:
+                raise ValueError(
+                    f"Local main branch ({local_main_commit}) is not "
+                    "up-to-date with upstream main branch "
+                    f"({upstream_main_commit}). Please pull the latest "
+                    "changes from upstream main branch first.")
+
+            # Then get the commit hash of the current branch that is the same as
+            # the upstream main commit.
             current_branch = subprocess.check_output(
                 ["git", "branch", "--show-current"]).decode("utf-8").strip()
 
@@ -279,6 +303,8 @@ class repackage_wheel(build_ext):
                 ["git", "merge-base", "main",
                  current_branch]).decode("utf-8").strip()
             return base_commit
+        except ValueError as err:
+            raise ValueError(err) from None
         except Exception as err:
             logger.warning(
                 "Failed to get the base commit in the main branch. "