[Minor] add nvcc note on bare_metal_version RuntimeError (#552)

* Add nvcc note on bare_metal_version `RuntimeError`

* Run Black formatting

setup.py

@@ -16,7 +16,12 @@ import urllib.error
 from wheel.bdist_wheel import bdist_wheel as _bdist_wheel
 
 import torch
-from torch.utils.cpp_extension import BuildExtension, CppExtension, CUDAExtension, CUDA_HOME
+from torch.utils.cpp_extension import (
+    BuildExtension,
+    CppExtension,
+    CUDAExtension,
+    CUDA_HOME,
+)
 
 
 with open("README.md", "r", encoding="utf-8") as fh:
@@ -28,7 +33,9 @@ this_dir = os.path.dirname(os.path.abspath(__file__))
 
 PACKAGE_NAME = "flash_attn"
 
-BASE_WHEEL_URL = "https://github.com/Dao-AILab/flash-attention/releases/download/{tag_name}/{wheel_name}"
+BASE_WHEEL_URL = (
+    "https://github.com/Dao-AILab/flash-attention/releases/download/{tag_name}/{wheel_name}"
+)
 
 # FORCE_BUILD: Force a fresh build locally, instead of attempting to find prebuilt wheels
 # SKIP_CUDA_BUILD: Intended to allow CI to use a simple `python setup.py sdist` run to copy over raw files, without any cuda compilation
@@ -44,15 +51,15 @@ def get_platform():
     """
     Returns the platform name as used in wheel filenames.
     """
-    if sys.platform.startswith('linux'):
+    if sys.platform.startswith("linux"):
-        return 'linux_x86_64'
+        return "linux_x86_64"
-    elif sys.platform == 'darwin':
+    elif sys.platform == "darwin":
-        mac_version = '.'.join(platform.mac_ver()[0].split('.')[:2])
+        mac_version = ".".join(platform.mac_ver()[0].split(".")[:2])
-        return f'macosx_{mac_version}_x86_64'
+        return f"macosx_{mac_version}_x86_64"
-    elif sys.platform == 'win32':
+    elif sys.platform == "win32":
-        return 'win_amd64'
+        return "win_amd64"
     else:
-        raise ValueError('Unsupported platform: {}'.format(sys.platform))
+        raise ValueError("Unsupported platform: {}".format(sys.platform))
 
 
 def get_cuda_bare_metal_version(cuda_dir):
@@ -107,7 +114,10 @@ if not SKIP_CUDA_BUILD:
     if CUDA_HOME is not None:
         _, bare_metal_version = get_cuda_bare_metal_version(CUDA_HOME)
         if bare_metal_version < Version("11.6"):
-            raise RuntimeError("FlashAttention is only supported on CUDA 11.6 and above")
+            raise RuntimeError(
+                "FlashAttention is only supported on CUDA 11.6 and above.  "
+                "Note: make sure nvcc has a supported version by running nvcc -V."
+            )
     # cc_flag.append("-gencode")
     # cc_flag.append("arch=compute_75,code=sm_75")
     cc_flag.append("-gencode")
@@ -191,16 +201,16 @@ if not SKIP_CUDA_BUILD:
                         "--use_fast_math",
                         # "--ptxas-options=-v",
                         # "--ptxas-options=-O2",
-                        "-lineinfo"
+                        "-lineinfo",
                     ]
                     + generator_flag
                     + cc_flag
                 ),
             },
             include_dirs=[
-                Path(this_dir) / 'csrc' / 'flash_attn',
+                Path(this_dir) / "csrc" / "flash_attn",
-                Path(this_dir) / 'csrc' / 'flash_attn' / 'src',
+                Path(this_dir) / "csrc" / "flash_attn" / "src",
-                Path(this_dir) / 'csrc' / 'cutlass' / 'include',
+                Path(this_dir) / "csrc" / "cutlass" / "include",
             ],
         )
     )
@@ -234,11 +244,8 @@ def get_wheel_url():
     cxx11_abi = str(torch._C._GLIBCXX_USE_CXX11_ABI).upper()
 
     # Determine wheel URL based on CUDA version, torch version, python version and OS
-    wheel_filename = f'{PACKAGE_NAME}-{flash_version}+cu{cuda_version}torch{torch_version}cxx11abi{cxx11_abi}-{python_version}-{python_version}-{platform_name}.whl'
+    wheel_filename = f"{PACKAGE_NAME}-{flash_version}+cu{cuda_version}torch{torch_version}cxx11abi{cxx11_abi}-{python_version}-{python_version}-{platform_name}.whl"
-    wheel_url = BASE_WHEEL_URL.format(
+    wheel_url = BASE_WHEEL_URL.format(tag_name=f"v{flash_version}", wheel_name=wheel_filename)
-        tag_name=f"v{flash_version}",
-        wheel_name=wheel_filename
-    )
     return wheel_url, wheel_filename
 
 
@@ -249,6 +256,7 @@ class CachedWheelsCommand(_bdist_wheel):
     the environment parameters to detect whether there is already a pre-built version of a compatible
     wheel available and short-circuits the standard full build pipeline.
     """
+
     def run(self):
         if FORCE_BUILD:
             return super().run()
@@ -280,7 +288,16 @@ setup(
     name=PACKAGE_NAME,
     version=get_package_version(),
     packages=find_packages(
-        exclude=("build", "csrc", "include", "tests", "dist", "docs", "benchmarks", "flash_attn.egg-info",)
+        exclude=(
+            "build",
+            "csrc",
+            "include",
+            "tests",
+            "dist",
+            "docs",
+            "benchmarks",
+            "flash_attn.egg-info",
+        )
     ),
     author="Tri Dao",
     author_email="trid@cs.stanford.edu",
@@ -294,11 +311,10 @@ setup(
         "Operating System :: Unix",
     ],
     ext_modules=ext_modules,
-    cmdclass={
+    cmdclass={"bdist_wheel": CachedWheelsCommand, "build_ext": BuildExtension}
-        'bdist_wheel': CachedWheelsCommand,
+    if ext_modules
-        "build_ext": BuildExtension
+    else {
-    } if ext_modules else {
+        "bdist_wheel": CachedWheelsCommand,
-        'bdist_wheel': CachedWheelsCommand,
     },
     python_requires=">=3.7",
     install_requires=[