…ion (#2908)

Summary:

Short term fix for #2901 to unblock
the 0.13.0 release.

Long version:
1. torchao's c++ kernels are not using libtorch and therefore are not
   guaranteed to work across different PyTorch versions
2. looks like we got lucky with (1) as torchao kernels just happened to
   work across PyTorch versions <= 2.8, but PyTorch nightlies in 2.9
   introduce a breaking ABI change (I don't know what specifically).
   Therefore, if we build torchao with torch 2.8, and then import it in
   an environment with torch 2.9+, the Python process will crash with
   `Aborted (core dumped)`.

For now, I just gate out the "known broken" case where we detect
that the torch version used to build torchao is < 2.9, and the torch
version in the environment when torchao is imported is >= 2.9. If this
is detected, this PR skips importing the `.so` files and logs a warning,
to at least have most of the torchao Python API still work and give the
user some information about how to get the custom kernels working.

For future releases, we'll need to make this more robust - leaving that
for future PRs.

Test Plan:

```bash
// install the 0.13.0 RC, built with PyTorch 2.8
with-proxy pip install torchao==0.13.0 --extra-index-url https://download.pytorch.org/whl/test/cu128

// copy over these changes to the local __init__.py file in the installation:
// ~/.conda/envs/pytorch_nightly/lib/python3.11/site-packages/torchao/__init__.py

// install PyTorch 2.9.x nightly
with-proxy pip3 install --pre torch --index-url https://download.pytorch.org/whl/nightly/cu128

// import torchao, verify no more crash and the warning message is emitted
(pytorch_nightly) [vasiliy@devgpu007.eag6 ~/local]$ python -X faulthandler -c "import torch; print(torch.__version__); import torchao"
2.9.0.dev20250829+cu128
Skipping import of cpp extensions due to incompatible torch version 2.9.0.dev20250829+cu128 for torchao version 0.13.0+cu128
```

Reviewers:

Subscribers:

Tasks:

Tags:

Summary:

Fix error in #2908. The version string for
PyTorch 2.8 reads "2.8.0...", so we need to compare `>= 2.9` to properly
gate out PyTorch 2.9.

Test Plan:

1. make this change in a locally installed __init__ file of torchao
   downloaded via pip
2. install PyTorch 2.8.0
3. import torchao, verify warning was not hit

Reviewers:

Subscribers:

Tasks:

Tags:

Summary:

Fix error in #2908. The version string for
PyTorch 2.8 reads "2.8.0...", so we need to compare `>= 2.9` to properly
gate out PyTorch 2.9.

Test Plan:

1. make this change in a locally installed __init__ file of torchao
   downloaded via pip
2. install PyTorch 2.8.0
3. import torchao, verify warning was not hit

Reviewers:

Subscribers:

Tasks:

Tags:

Summary:

Fix error in #2908. The version string for
PyTorch 2.8 reads "2.8.0...", so we need to compare `>= 2.9` to properly
gate out PyTorch 2.9.

Test Plan:

1. make this change in a locally installed __init__ file of torchao
   downloaded via pip
2. install PyTorch 2.8.0
3. import torchao, verify warning was not hit

Reviewers:

Subscribers:

Tasks:

Tags:

Summary:

Undoes part of #2908 to make
the message about missing `.so` files be a debug print instead of a
warning.  Reason: this always happens for builds without executorch ops.

Keeps the version mismatch log as a warning.

Test Plan:

Make this change locally in an install of torchao on an H100, verify
warning no longer prints.

Reviewers:

Subscribers:

Tasks:

Tags:

Summary:

Undoes part of #2908 to make
the message about missing `.so` files be a debug print instead of a
warning.  Reason: this always happens for builds without executorch ops.

Keeps the version mismatch log as a warning.

Test Plan:

Make this change locally in an install of torchao on an H100, verify
warning no longer prints.

Reviewers:

Subscribers:

Tasks:

Tags:

Summary:

Undoes part of #2908 to make
the message about missing `.so` files be a debug print instead of a
warning.  Reason: this always happens for builds without executorch ops.

Keeps the version mismatch log as a warning.

Test Plan:

Make this change locally in an install of torchao on an H100, verify
warning no longer prints.

Reviewers:

Subscribers:

Tasks:

Tags: