fix fa2 and fa4 conflict

[qzzz95]

No description provided.

[gemini-code-assist]

Code Review

This pull request updates the Flash Attention 2 availability check in diffsynth_engine/utils/flag.py to target the specific flash_attn.flash_attn_func module. A review comment suggests implementing a more robust try-except block to ensure the check accurately reflects how the module is imported elsewhere in the codebase, preventing potential runtime errors.

[gemini-code-assist]

The check for Flash Attention 2 availability is not fully robust. It verifies that the flash_attn.flash_attn_func module can be imported, but the code in diffsynth_engine/models/basic/attention.py uses from flash_attn import flash_attn_func. This requires flash_attn_func to be an attribute of the top-level flash_attn package.

These two conditions are not always equivalent. A more robust approach would be to verify the attribute's existence directly by attempting the import. This prevents potential ImportError at runtime if the flash-attn package structure changes.

Suggested change

	FLASH_ATTN_2_AVAILABLE = check_module_available("flash_attn.flash_attn_func", "Flash attention 2")
	try:
	from flash_attn import flash_attn_func
	logger.info("Flash attention 2 is available")
	FLASH_ATTN_2_AVAILABLE = True
	except (ImportError, AttributeError):
	logger.info("Flash attention 2 is not available")
	FLASH_ATTN_2_AVAILABLE = False