Keep the newer-mapper probe alive when the fetched mapper has no fp8 tables (#7497)

* Keep the newer-mapper probe alive when the fetched mapper has no fp8 tables

_get_new_mapper reads the two fp8 tables out of the fetched mapper.py under
that file's own names, unlike the three NEW_ names it renames itself. A
mapper.py that does not define them raises KeyError, the bare except swallows
it, and the function returns five empty dicts, so the 4bit and 16bit upgrade
check stops firing as well. That check is the reason the probe exists.

Every mapper.py older than the fp8 tables is such a file: fetching the
2025-11-07 one leaves the probe with [0, 0, 0, 0, 0] instead of
[400, 997, 591]. Reading the two names with .get keeps the 4bit half working
and empties only the fp8 half, which costs nothing, since the probe runs only
after the installed tables have already missed.

Add a regression test that also pins the fetched-only fp8 upgrade error, which
the existing test cannot catch: it serves the repo's own mapper.py as both the
installed and the fetched source, so any fresh dict satisfies its identity
assertions.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

tests/test_new_mapper_fetched_fp8.py

@@ -0,0 +1,155 @@
+# SPDX-License-Identifier: AGPL-3.0-only
+# Copyright 2026-present the Unsloth AI Inc. team. All rights reserved.
+
+"""Regression tests for what ``_get_new_mapper`` hands back to the upgrade probe.
+
+``test_new_mapper_no_global_leak.py`` serves the repo's own ``mapper.py`` as both installed
+and fetched source, so it cannot tell a fetched table from a fresh copy of the installed one.
+Two gaps it misses:
+
+1. The probe must answer for an fp8 repo only the FETCHED mapper knows, so an extra ``"8"``
+   entry is spliced into the fetched source only. Isolating the exec without returning the
+   fetched fp8 tables would silently drop the fp8 half of the upgrade check.
+2. The probe must survive a fetched ``mapper.py`` with no fp8 tables (anything older, or a
+   future rename): reading them with ``[]`` raises ``KeyError`` into the bare ``except``,
+   taking the 4bit half, the probe's whole purpose, down with it.
+
+``loader_utils`` imports torch, so ast-extract the resolvers and run them against a stubbed
+``requests``, as in ``tests/test_bad_mappings_redirect.py``.
+"""
+
+import ast
+import os
+import sys
+import types
+
+_MODELS = os.path.join(os.path.dirname(__file__), os.pardir, "unsloth", "models")
+
+_WANTED = {"__get_model_name", "_resolve_with_mappers", "_get_new_mapper", "get_model_name"}
+
+# An fp8 ("8") model, spliced into the FETCHED mapper only.
+_NEW_KEY = "unsloth/Zeta-9B-Only-On-Main"
+_NEW_OFFICIAL = "zeta-org/Zeta-9B-Only-On-Main-FP8"
+_NEW_BLOCK = "unsloth/Zeta-9B-Only-On-Main-FP8-Block"
+_NEW_ROW = "unsloth/Zeta-9B-Only-On-Main-FP8-Row"
+_ANCHOR = '    "unsloth/Kimi-K2-Instruct-BF16" : ('
+
+
+def _mapper_source():
+    with open(os.path.join(_MODELS, "mapper.py"), encoding = "utf-8") as f:
+        return f.read()
+
+
+def _with_extra_fp8_model(source):
+    assert _ANCHOR in source, "anchor moved; update this test"
+    entry = (
+        f'    "{_NEW_KEY}" : {{\n'
+        f'        "16" : ("{_NEW_KEY}", "zeta-org/Zeta-9B-Only-On-Main"),\n'
+        f'        "8"  : ("{_NEW_OFFICIAL}", "{_NEW_BLOCK}", "{_NEW_ROW}"),\n'
+        f"    }},\n"
+    )
+    return source.replace(_ANCHOR, entry + _ANCHOR, 1)
+
+
+def _without_fp8_tables(source):
+    """A mapper.py from before the fp8 tables existed."""
+    return source.replace("FLOAT_TO_FP8_BLOCK_MAPPER", "SOME_OTHER_BLOCK_TABLE").replace(
+        "FLOAT_TO_FP8_ROW_MAPPER", "SOME_OTHER_ROW_TABLE"
+    )
+
+
+class _FakeResponse:
+    def __init__(self, text):
+        self.text = text
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *exc):
+        return False
+
+
+def _install_fake_requests(monkeypatch, text):
+    module = types.ModuleType("requests")
+    module.get = lambda url, timeout = None: _FakeResponse(text)
+    monkeypatch.setitem(sys.modules, "requests", module)
+
+
+def _install_fake_vllm_absent(monkeypatch, namespace):
+    """vllm >= 0.12.0 returns early from __get_model_name, leaving the probe unreachable."""
+    monkeypatch.delitem(sys.modules, "vllm", raising = False)
+    fake = types.ModuleType("importlib")
+    fake.util = types.SimpleNamespace(find_spec = lambda name: None)
+    namespace["importlib"] = fake
+
+
+def _load_resolver(installed_source):
+    """Stand-in for loader_utils' module globals, built from `installed_source`."""
+    from unsloth_zoo.utils import Version
+
+    mapper_ns = {}
+    exec(compile(installed_source, "mapper.py", "exec"), mapper_ns)
+
+    namespace = {
+        "INT_TO_FLOAT_MAPPER": mapper_ns["INT_TO_FLOAT_MAPPER"],
+        "FLOAT_TO_INT_MAPPER": mapper_ns["FLOAT_TO_INT_MAPPER"],
+        "MAP_TO_UNSLOTH_16bit": mapper_ns["MAP_TO_UNSLOTH_16bit"],
+        "FLOAT_TO_FP8_BLOCK_MAPPER": mapper_ns["FLOAT_TO_FP8_BLOCK_MAPPER"],
+        "FLOAT_TO_FP8_ROW_MAPPER": mapper_ns["FLOAT_TO_FP8_ROW_MAPPER"],
+        "SUPPORTS_FOURBIT": True,
+        "transformers_version": Version("4.57.6"),
+        "Version": Version,
+        "os": os,
+    }
+    with open(os.path.join(_MODELS, "loader_utils.py"), encoding = "utf-8") as f:
+        tree = ast.parse(f.read())
+    for node in tree.body:
+        if isinstance(node, ast.Assign) and any(
+            getattr(t, "id", None) in ("BAD_MAPPINGS", "_OFFLINE_ENV_VALUES", "_OFFLINE_ENV_KEYS")
+            for t in node.targets
+        ):
+            exec(compile(ast.Module([node], []), "<assign>", "exec"), namespace)
+        elif isinstance(node, ast.FunctionDef) and (
+            node.name in _WANTED or node.name == "_env_says_offline"
+        ):
+            exec(compile(ast.Module([node], []), node.name, "exec"), namespace)
+    return namespace
+
+
+def test_probe_answers_for_an_fp8_repo_only_the_fetched_mapper_knows(monkeypatch):
+    installed = _mapper_source()
+    namespace = _load_resolver(installed)
+    installed_block = namespace["FLOAT_TO_FP8_BLOCK_MAPPER"]
+    installed_row = namespace["FLOAT_TO_FP8_ROW_MAPPER"]
+    assert _NEW_OFFICIAL.lower() not in installed_block, "the installed table must not know it"
+
+    _install_fake_requests(monkeypatch, _with_extra_fp8_model(installed))
+    _install_fake_vllm_absent(monkeypatch, namespace)
+
+    try:
+        resolved = namespace["get_model_name"](
+            _NEW_OFFICIAL, load_in_4bit = False, load_in_fp8 = "block"
+        )
+    except NotImplementedError as error:
+        assert "not supported in your current Unsloth version" in str(error)
+    else:
+        raise AssertionError(
+            f"a fetched-only fp8 repo must raise the upgrade error, got {resolved!r}"
+        )
+
+    # Answering must not have adopted the fetched tables.
+    assert namespace["FLOAT_TO_FP8_BLOCK_MAPPER"] is installed_block
+    assert namespace["FLOAT_TO_FP8_ROW_MAPPER"] is installed_row
+    assert _NEW_OFFICIAL.lower() not in namespace["FLOAT_TO_FP8_BLOCK_MAPPER"]
+
+
+def test_probe_survives_a_fetched_mapper_without_the_fp8_tables(monkeypatch):
+    installed = _mapper_source()
+    namespace = _load_resolver(installed)
+    _install_fake_requests(monkeypatch, _without_fp8_tables(installed))
+
+    int_to_float, float_to_int, map_to_16bit = namespace["_get_new_mapper"]()[:3]
+
+    assert (
+        int_to_float and float_to_int and map_to_16bit
+    ), "a fetched mapper.py without the fp8 tables must not take the 4bit upgrade check down"