fix: map None quant method to q8_0 before lowercasing in GGUF export (#6889)

tests/saving/test_quant_method_none_normalization.py

@@ -0,0 +1,81 @@
+"""CPU-only regression for the quant-method normalization loops in save.py.
+
+`unsloth_save_pretrained_gguf` and `save_to_gguf_generic` each normalize the
+`quantization_method` list, mapping a ``None`` element to ``"q8_0"``. The mapping
+used to call ``quant_method.lower()`` as the first statement of the loop, so a
+``None`` element (e.g. ``quantization_method=[None]`` or ``["q4_k_m", None]``)
+raised ``AttributeError: 'NoneType' object has no attribute 'lower'`` and the
+``elif quant_method is None`` branch was unreachable dead code.
+
+The loop is inline inside two heavy functions (importing unsloth needs
+unsloth_zoo / a GPU), so - like test_is_gpt_oss_detection.py - we extract just the
+loop source via ``ast`` and exec it against sample inputs. That exercises the real
+source: it fails on the old ordering and passes once ``None`` is handled first.
+"""
+
+from __future__ import annotations
+
+import ast
+from pathlib import Path
+
+import pytest
+
+SAVE_PY = Path(__file__).resolve().parents[2] / "unsloth" / "save.py"
+SAVE_SRC = SAVE_PY.read_text(encoding = "utf-8")
+SAVE_TREE = ast.parse(SAVE_SRC, filename = str(SAVE_PY))
+
+# The target functions and the list variable each one appends the normalized method to.
+TARGETS = (
+    ("unsloth_save_pretrained_gguf", "quantization_methods"),
+    ("save_to_gguf_generic", "new_quantization_methods"),
+)
+
+
+def _func(tree, name):
+    for node in ast.walk(tree):
+        if isinstance(node, ast.FunctionDef) and node.name == name:
+            return node
+    raise AssertionError(f"function {name!r} not found in {SAVE_PY.name}")
+
+
+def _quant_loop(func_name):
+    # The quant-normalization `for` loop iterates `quantization_method`; grab its source.
+    func = _func(SAVE_TREE, func_name)
+    for node in ast.walk(func):
+        if (
+            isinstance(node, ast.For)
+            and isinstance(node.iter, ast.Call)
+            and isinstance(node.iter.func, ast.Name)
+            and node.iter.func.id == "enumerate"
+            and isinstance(node.iter.args[0], ast.Name)
+            and node.iter.args[0].id == "quantization_method"
+        ):
+            return node
+    raise AssertionError(f"quant-normalization loop not found in {func_name}")
+
+
+def _run_loop(func_name, out_var, quantization_method):
+    # exec just the extracted loop against a given input, returning the appended methods.
+    loop_src = ast.get_source_segment(SAVE_SRC, _quant_loop(func_name))
+    namespace = {out_var: [], "quantization_method": quantization_method}
+    exec(loop_src, {"__builtins__": __builtins__}, namespace)
+    return namespace[out_var]
+
+
+@pytest.mark.parametrize("func_name, out_var", TARGETS)
+def test_none_element_maps_to_q8_0(func_name, out_var):
+    # A bare None inside the list must map to q8_0, not raise AttributeError.
+    assert _run_loop(func_name, out_var, [None]) == ["q8_0"]
+
+
+@pytest.mark.parametrize("func_name, out_var", TARGETS)
+def test_none_mixed_with_strings(func_name, out_var):
+    # None resolves to q8_0 while sibling string methods are still normalized (lowercased).
+    assert _run_loop(func_name, out_var, ["Q4_K_M", None]) == ["q4_k_m", "q8_0"]
+
+
+@pytest.mark.parametrize("func_name, out_var", TARGETS)
+def test_string_methods_unchanged(func_name, out_var):
+    # The fix must not alter behavior for the ordinary string inputs.
+    methods = ["not_quantized", "fast_quantized", "quantized", "Q8_0"]
+    assert _run_loop(func_name, out_var, methods) == ["f16", "q8_0", "q4_k_m", "q8_0"]

unsloth/save.py

@@ -2926,15 +2926,16 @@ def unsloth_save_pretrained_gguf(
                 "Unsloth: quantization_method can only be a string or a list of strings"
             )
         for i, quant_method in enumerate(quantization_method):
-            quant_method = quant_method.lower()
+            if quant_method is None:
+                quant_method = "q8_0"
+            else:
+                quant_method = quant_method.lower()
             if quant_method == "not_quantized":
                 quant_method = "f16"
             elif quant_method == "fast_quantized":
                 quant_method = "q8_0"
             elif quant_method == "quantized":
                 quant_method = "q4_k_m"
-            elif quant_method is None:
-                quant_method = "q8_0"
             quantization_methods.append(quant_method.lower())
 
     try:
@@ -3727,15 +3728,16 @@ def save_to_gguf_generic(
                 "Unsloth: quantization_method can only be a string or a list of strings"
             )
         for i, quant_method in enumerate(quantization_method):
-            quant_method = quant_method.lower()
+            if quant_method is None:
+                quant_method = "q8_0"
+            else:
+                quant_method = quant_method.lower()
             if quant_method == "not_quantized":
                 quant_method = "f16"
             elif quant_method == "fast_quantized":
                 quant_method = "q8_0"
             elif quant_method == "quantized":
                 quant_method = "q4_k_m"
-            elif quant_method is None:
-                quant_method = "q8_0"
             new_quantization_methods.append(quant_method.lower())
     else:
         new_quantization_methods.append(quantization_type.lower())