filter flash_attn optional imports loading remote code (#30954)

* filter flash_attn optional imports loading remote code

* improve pattern

* fix code style

* Update src/transformers/dynamic_module_utils.py
Co-authored-by: Matt <Rocketknight1@users.noreply.github.com>

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Co-authored-by: Matt <Rocketknight1@users.noreply.github.com>

src/transformers/dynamic_module_utils.py

@@ -149,6 +149,10 @@ def get_imports(filename: Union[str, os.PathLike]) -> List[str]:
 
     # filter out try/except block so in custom code we can have try/except imports
     content = re.sub(r"\s*try\s*:\s*.*?\s*except\s*.*?:", "", content, flags=re.MULTILINE | re.DOTALL)
+    # filter out imports under is_flash_attn_2_available block for avoid import issues in cpu only environment
+    content = re.sub(
+        r"if is_flash_attn[a-zA-Z0-9_]+available\(\):\s*(from flash_attn\s*.*\s*)+", "", content, flags=re.MULTILINE
+    )
 
     # Imports of the form `import xxx`
     imports = re.findall(r"^\s*import\s+(\S+)\s*$", content, flags=re.MULTILINE)