Fix BAD_MAPPINGS not redirecting the -unsloth-bnb-4bit dynamic quants (#6949)

---------

Co-authored-by: oobabooga <112222186+oobabooga@users.noreply.github.com>

.github/workflows/consolidated-tests-ci.yml

@@ -364,6 +364,7 @@ jobs:
             tests/utils/test_attention_masks.py \
             tests/utils/test_trunc_normal_patch.py \
             tests/python/test_fast_language_model_text_only.py \
+            tests/test_bad_mappings_redirect.py \
             tests/test_prefetch_snapshot_scope.py \
             --deselect 'tests/utils/test_attention_masks.py::test_run_attention_flash_varlen_receives_window_and_softcap'
           # The deselected test monkeypatches flash_attn_varlen_func, which is

tests/test_bad_mappings_redirect.py

@@ -0,0 +1,47 @@
+"""Regression test for BAD_MAPPINGS redirecting oversized dynamic quants.
+
+get_model_name previously applied BAD_MAPPINGS only to the resolver's output,
+but several listed names (the `-unsloth-bnb-4bit` dynamic quants, plus any name
+the resolver doesn't map) come back as None, so their BAD_MAPPINGS entries were
+dead and the oversized model loaded. Asserting over every entry catches all of
+them. The mapper table and the resolver have no heavy imports of their own,
+so we exec the import-free mapper module and ast-extract the resolver functions
+rather than importing unsloth (which needs a GPU).
+"""
+
+import ast
+import os
+
+_MODELS = os.path.join(os.path.dirname(__file__), os.pardir, "unsloth", "models")
+
+
+def _load_get_model_name():
+    mapper_ns = {}
+    with open(os.path.join(_MODELS, "mapper.py"), encoding = "utf-8") as f:
+        exec(compile(f.read(), "mapper.py", "exec"), mapper_ns)
+
+    with open(os.path.join(_MODELS, "loader_utils.py"), encoding = "utf-8") as f:
+        tree = ast.parse(f.read())
+
+    namespace = dict(mapper_ns)
+    namespace["SUPPORTS_FOURBIT"] = True
+    namespace["_env_says_offline"] = lambda: True
+    namespace["_get_new_mapper"] = lambda: ({}, {}, {})
+
+    wanted = {"__get_model_name", "_resolve_with_mappers", "get_model_name"}
+    for node in tree.body:
+        if isinstance(node, ast.Assign) and any(
+            getattr(target, "id", None) == "BAD_MAPPINGS" for target in node.targets
+        ):
+            exec(compile(ast.Module([node], []), "<bad_mappings>", "exec"), namespace)
+        elif isinstance(node, ast.FunctionDef) and node.name in wanted:
+            exec(compile(ast.Module([node], []), node.name, "exec"), namespace)
+
+    return namespace["get_model_name"], namespace["BAD_MAPPINGS"]
+
+
+def test_bad_mappings_redirect_every_listed_name():
+    get_model_name, bad_mappings = _load_get_model_name()
+    assert bad_mappings, "BAD_MAPPINGS should not be empty"
+    for name, expected in bad_mappings.items():
+        assert get_model_name(name, load_in_4bit = True) == expected, name

unsloth/models/loader_utils.py

@@ -239,6 +239,11 @@ def get_model_name(
         and new_model_name.lower() in BAD_MAPPINGS
     ):
         new_model_name = BAD_MAPPINGS[new_model_name.lower()]
+    elif new_model_name is None and model_name.lower() in BAD_MAPPINGS:
+        # Some bad names (e.g. the `-unsloth-bnb-4bit` dynamic quants) are keys
+        # of the mappers, not values, so the resolver returns None for them and
+        # the remap above is skipped; remap the input name directly instead.
+        new_model_name = BAD_MAPPINGS[model_name.lower()]
 
     if (
         new_model_name is None