Embed git commit hash into Python source (#319)

This PR performs a simple embed of the current git commit hash into the
Python source:

1. The hash itself is defined in the ~`__githash__`~ `__commit__` var in
`vllm/version.py` alongside `__version__`
2. `vllm/__init__.py` is updated to (a) import ~`__githash__`~
`__commit__` and (b) include it in the `__all__` list

As a result, you can now do the following:

```python
import vllm
print(vllm.__version__)  # already present
print(vllm.__commit__)  # now available
```

**Test Plan**
New test added which minimally verifies that this new variable is
defined to a value with a bare-minimum length.

setup.py

@@ -6,6 +6,7 @@
 import re
 import subprocess
 import sys
+import warnings
 from shutil import which
 from typing import Dict, List
 
@@ -27,6 +28,33 @@ def load_module_from_path(module_name, path):
 ROOT_DIR = os.path.dirname(__file__)
 logger = logging.getLogger(__name__)
 
+
+def embed_commit_hash():
+    try:
+        commit_id = subprocess.check_output(["git", "rev-parse", "HEAD"],
+                                            encoding="utf-8").strip()
+
+        version_file = os.path.join(ROOT_DIR, "vllm", "version.py")
+        with open(version_file, encoding="utf-8") as f:
+            version_contents = f.read()
+
+        version_contents = version_contents.replace("COMMIT_HASH_PLACEHOLDER",
+                                                    f"{commit_id}")
+
+        with open(version_file, "w", encoding="utf-8") as f:
+            f.write(version_contents)
+    except subprocess.CalledProcessError as e:
+        warnings.warn(f"failed to get commit hash:\n{e}",
+                      RuntimeWarning,
+                      stacklevel=2)
+    except Exception as e:
+        warnings.warn(f"failed to embed commit hash:\n{e}",
+                      RuntimeWarning,
+                      stacklevel=2)
+
+
+embed_commit_hash()
+
 # cannot import envs directly because it depends on vllm,
 #  which is not installed yet
 envs = load_module_from_path('envs', os.path.join(ROOT_DIR, 'vllm', 'envs.py'))

tests/test_embedded_commit.py

@@ -0,0 +1,5 @@
+import vllm
+
+
+def test_embedded_commit_defined():
+    assert len(vllm.__commit__) > 7

vllm/__init__.py

@@ -12,9 +12,10 @@
 from vllm.pooling_params import PoolingParams
 from vllm.sampling_params import SamplingParams
 
-from .version import __version__
+from .version import __commit__, __version__
 
 __all__ = [
+    "__commit__",
     "__version__",
     "LLM",
     "ModelRegistry",

vllm/version.py

@@ -1,2 +1,3 @@
 # UPSTREAM SYNC: take downstream
 __version__ = "0.5.1"
+__commit__ = "COMMIT_HASH_PLACEHOLDER"