From 9a22d32efea8a13778ea44d6f7b4e25f39a8fb3a Mon Sep 17 00:00:00 2001
From: arham766 <arhamislam766@yahoo.com>
Date: Mon, 6 Jul 2026 21:48:55 -0700
Subject: [PATCH] fix: reject amax assignment on dynamic quantizers

Setting amax on a dynamic TensorQuantizer silently stored a value that
dynamic quantization never uses; fail fast instead. getattr (not
self._dynamic) because __init__ assigns self.amax = amax before
set_from_attribute_config creates the _dynamic attribute.

Also adds a regression test pinning the disabled extra_repr detail
output (dead code until #1879 made it reachable).

Signed-off-by: arham766 <arhamislam766@yahoo.com>
---
 .../nn/modules/tensor_quantizer.py            |  6 ++++++
 .../quantization/test_tensor_quantizer_cpu.py | 19 +++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/modelopt/torch/quantization/nn/modules/tensor_quantizer.py b/modelopt/torch/quantization/nn/modules/tensor_quantizer.py
index c7649f9383d..dcb92a1a4a4 100644
--- a/modelopt/torch/quantization/nn/modules/tensor_quantizer.py
+++ b/modelopt/torch/quantization/nn/modules/tensor_quantizer.py
@@ -348,6 +348,12 @@ def amax(self):
     @amax.setter
     def amax(self, value):
         assert value is not None, "amax cannot be set to None."
+        # getattr (not self._dynamic): __init__ assigns self.amax = amax before
+        # set_from_attribute_config creates the _dynamic attribute, so a bare
+        # attribute access would break the amax= constructor argument.
+        assert not getattr(self, "_dynamic", False), (
+            "Dynamic quantization does not have fixed amax; amax cannot be set."
+        )
 
         if not isinstance(value, torch.Tensor):
             value = torch.tensor(value)
diff --git a/tests/unit/torch/quantization/test_tensor_quantizer_cpu.py b/tests/unit/torch/quantization/test_tensor_quantizer_cpu.py
index 56019d8cf75..60eb4e493cd 100644
--- a/tests/unit/torch/quantization/test_tensor_quantizer_cpu.py
+++ b/tests/unit/torch/quantization/test_tensor_quantizer_cpu.py
@@ -15,16 +15,35 @@
 
 """Tests of tensor quantizer."""
 
+import pytest
+import torch
 from _test_utils.torch.quantization.tensor_quantizer_common import (
     BlockQuantTester,
     SequentialQuantizerTester,
     TensorQuantizerTester,
 )
 
+from modelopt.torch.quantization.config import QuantizerAttributeConfig
+from modelopt.torch.quantization.nn import TensorQuantizer
+
 
 class TestTensorQuantizerCPU(TensorQuantizerTester):
     device = "cpu"
 
+    def test_disabled_extra_repr(self):
+        quantizer = TensorQuantizer(QuantizerAttributeConfig(enable=False)).to(self.device)
+        assert quantizer.extra_repr() == "disabled"
+
+        quantizer.pre_quant_scale = torch.tensor([0.5, 2.0]).to(self.device)
+        extra_repr = quantizer.extra_repr()
+        assert extra_repr.startswith("disabled")
+        assert "pre_quant_scale=" in extra_repr
+
+    def test_dynamic_amax_set_rejected(self):
+        quantizer = TensorQuantizer(QuantizerAttributeConfig(type="dynamic")).to(self.device)
+        with pytest.raises(AssertionError, match="Dynamic quantization"):
+            quantizer.amax = 1.0
+
 
 class TestBlockQuantCPU(BlockQuantTester):
     device = "cpu"