tests: add regression test for logger NameError in torchao_quantizer (fixes #13104)

Add a test to prevent regression of the NameError that occurred when
`logger` was used inside `_update_torch_safe_globals()` before being
defined at module level. The fix (moving `logger` before the function)
was included in PR #12901, but this test ensures it cannot regress.

Author: dhruvildarji

tests/quantization/torchao/test_torchao.py

@@ -72,6 +72,47 @@
         from torchao.quantization import Int8WeightOnlyConfig
 
 
+class TorchAoQuantizerModuleTest(unittest.TestCase):
+    def test_logger_defined_before_module_level_code(self):
+        """
+        Regression test for https://github.com/huggingface/diffusers/issues/13104.
+        Ensures that `logger` is defined at the module level in torchao_quantizer.py
+        before any module-level code that uses it (such as `_update_torch_safe_globals`).
+        Previously, `logger` was defined after the function that uses it, causing a
+        `NameError: name 'logger' is not defined` at import time when the exception
+        handler in `_update_torch_safe_globals` was triggered.
+        """
+        import ast
+        import inspect
+
+        from diffusers.quantizers.torchao import torchao_quantizer
+
+        source = inspect.getsource(torchao_quantizer)
+        tree = ast.parse(source)
+
+        logger_lineno = None
+        func_lineno = None
+
+        for node in ast.walk(tree):
+            if isinstance(node, ast.Assign):
+                for target in node.targets:
+                    if isinstance(target, ast.Name) and target.id == "logger":
+                        logger_lineno = node.lineno
+            if isinstance(node, ast.FunctionDef) and node.name == "_update_torch_safe_globals":
+                func_lineno = node.lineno
+
+        self.assertIsNotNone(logger_lineno, "logger must be defined at module level in torchao_quantizer.py")
+        self.assertIsNotNone(
+            func_lineno, "_update_torch_safe_globals must be defined in torchao_quantizer.py"
+        )
+        self.assertLess(
+            logger_lineno,
+            func_lineno,
+            f"logger (line {logger_lineno}) must be defined before _update_torch_safe_globals "
+            f"(line {func_lineno}) to avoid NameError at import time (see issue #13104)",
+        )
+
+
 @require_torch
 @require_torch_accelerator
 @require_torchao_version_greater_or_equal("0.7.0")