Fix fetch build fallback

[SunMarc]

What does this PR do ?

Currently, when trying to kernelize a model or a layer but the kernel repo doesn't have a build that is compatible with our hardware, we will have a hard failure instead of fallback. Not sure if this is intended or not ?

This is an issue I had when testing kernels with transformers with use_kernels=True

>>> model = AutoModelForCausalLM.from_pretrained(
...       "trl-internal-testing/tiny-Qwen2ForCausalLM-2.5",
...       device_map="cuda:0",
...   )
Loading weights: 100%|███████████████████████████████████████████████████████████| 27/27 [00:00<00:00, 131.42it/s]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/admin/home/marc/transformers/.claude/worktrees/fsdp-meta/src/transformers/models/auto/auto_factory.py", line 409, in from_pretrained
    return model_class.from_pretrained(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/admin/home/marc/transformers/.claude/worktrees/fsdp-meta/src/transformers/modeling_utils.py", line 4390, in from_pretrained
    model.set_use_kernels(use_kernels, kernel_config, kernels_mode)
  File "/admin/home/marc/transformers/.claude/worktrees/fsdp-meta/src/transformers/modeling_utils.py", line 3828, in set_use_kernels
    kernelize(self)
  File "/admin/home/marc/transformers/.claude/worktrees/fsdp-meta/src/transformers/integrations/hub_kernels.py", line 947, in kernelize
    _kernels_kernelize(model, device=device, mode=used_mode)
  File "/admin/home/marc/miniconda3/envs/test_bis/lib/python3.11/site-packages/kernels/layer/kernelize.py", line 267, in kernelize
    kernelize_layer(
  File "/admin/home/marc/miniconda3/envs/test_bis/lib/python3.11/site-packages/kernels/layer/layer.py", line 526, in kernelize_layer
    layer = _get_layer_memoize(repo, module_class)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/admin/home/marc/miniconda3/envs/test_bis/lib/python3.11/site-packages/kernels/layer/layer.py", line 659, in _get_layer_memoize
    layer = repo.load()
            ^^^^^^^^^^^
  File "/admin/home/marc/miniconda3/envs/test_bis/lib/python3.11/site-packages/kernels/layer/layer.py", line 116, in load
    kernel = get_kernel(
             ^^^^^^^^^^^
  File "/admin/home/marc/miniconda3/envs/test_bis/lib/python3.11/site-packages/kernels/load.py", line 168, in get_kernel
    return get_kernel_with_resolver(
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/admin/home/marc/miniconda3/envs/test_bis/lib/python3.11/site-packages/kernels/load.py", line 85, in get_kernel_with_resolver
    tree = resolve_kernel_tree(
           ^^^^^^^^^^^^^^^^^^^^
  File "/admin/home/marc/miniconda3/envs/test_bis/lib/python3.11/site-packages/kernels/deps.py", line 111, in resolve_kernel_tree
    location = resolver.resolve(api=api, backend=backend, kernel=kernel) if resolver else None
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/admin/home/marc/miniconda3/envs/test_bis/lib/python3.11/site-packages/kernels/resolver.py", line 257, in resolve
    location = resolver.resolve(api=api, backend=backend, kernel=kernel)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/admin/home/marc/miniconda3/envs/test_bis/lib/python3.11/site-packages/kernels/resolver.py", line 284, in resolve
    return resolve_hub_kernel(kernel.repo_id, api=api, revision=revision, backend=backend)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[github-actions]

Hi @SunMarc, thanks for your interest in contributing!

This project requires that pull request authors are vouched, and you are not in the list of vouched users.

This PR will be closed automatically. See https://github.com/huggingface/kernels/blob/main/CONTRIBUTING.md for more details.

[SunMarc]

;)

[danieldk]

In this case, since there is a layer/device/repo registered, it might be good to emit a logging.warning that there is no correct build variant.

[SunMarc]

okay will do ! maybe logging.info instead ? I feel like it will be too verbose otherwise, especially in transformers

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[github-actions]

Coverage report — kernels/

Measured on: Python 3.10 / Torch 2.13.0.
Other CI configurations are not included in this number.
Hardware-gated code paths (ROCm/XPU/NPU/Darwin/Windows) are excluded or unreachable on the Linux+CUDA runner.

Total coverage: 87.3% — threshold: 80% — ✅

Per-file breakdown

Name	Stmts	Miss	Cover	Missing
src/kernels/__init__.py	14	0	100%
src/kernels/_system.py	6	1	83%	10
src/kernels/_versions.py	130	14	89%	53, 59-60, 63-64, 102, 165-170, 199, 219
src/kernels/archs.py	56	1	98%	94
src/kernels/backends.py	213	62	71%	42, 46, 50-53, 70, 92, 110, 119, 123, 127-129, 150, 159, 163, 167-169, 190, 201, 203, 210-213, 226, 230, 234-254, 262, 285-305
src/kernels/compat.py	9	1	89%	5
src/kernels/deps.py	70	1	99%	56
src/kernels/hf_hub.py	63	2	97%	21, 23
src/kernels/importer.py	44	5	89%	80, 84, 87, 101-102
src/kernels/install.py	21	7	67%	76-100
src/kernels/layer/__init__.py	6	0	100%
src/kernels/layer/_interval_tree.py	103	4	96%	23, 52, 147, 150
src/kernels/layer/device.py	48	14	71%	42, 47-49, 91, 96-98, 101, 149, 152, 155-157
src/kernels/layer/func.py	85	6	93%	90, 115, 191, 311, 338, 368
src/kernels/layer/globals.py	5	0	100%
src/kernels/layer/kernelize.py	82	8	90%	259, 297, 305-306, 312, 316, 332-334
src/kernels/layer/layer.py	232	14	94%	207, 254, 281, 415, 495-496, 517, 525, 536, 576, 580, 593, 646, 676
src/kernels/layer/mode.py	14	0	100%
src/kernels/layer/repos.py	144	42	71%	27, 33, 36-43, 63-64, 70, 73-76, 90, 94, 103-104, 110, 113-116, 123-124, 130, 133-136, 143-144, 150, 153-156, 163-164, 170, 173-176, 257
src/kernels/load.py	71	2	97%	338, 378
src/kernels/locking.py	89	64	28%	35-83, 91-98, 102-125, 137, 152-159, 165-175, 179-186
src/kernels/python_deps.py	58	6	90%	59-60, 64-65, 101, 104
src/kernels/resolver.py	156	2	99%	220, 226
src/kernels/status.py	50	2	96%	25, 79
src/kernels/validate.py	88	5	94%	9, 100, 167, 190-191
src/kernels/variants.py	278	19	93%	65, 96, 117, 147, 256-257, 299-302, 304, 388-394, 400-406, 437-443, 455-461
src/kernels/verify.py	127	6	95%	46, 202-204, 318-319
TOTAL	2262	288	87%

Updated by the Test kernels workflow on commit df7d1574924f2103f0c60a2fe7cf4328680d8fec.

[SunMarc]

cc @danieldk

[danieldk]

Super nice!

Now that I see the top-level export, I think it might be better to call this KernelizeFallback to add a bit of scoping.