Fixes#141563
In NumPy, an ellipsis always acts as a separator between advanced indices, even when the ellipsis doesn't actually match any dimensions. In PyTorch an empty ellipsis doesn't cause a separation. This leads to differing behavior between Numpy and PyTorch in this edge case.
This difference in behavior leads to a bug when using torch.compile:
```python
>>> import numpy as np
>>> f = lambda x: x[:,(0,1),...,(0,1)].shape
>>> a = np.ones((3, 4, 5))
>>> f(a)
(2, 3)
>>> torch.compile(f)(a)
(3, 2)
```
Similarly to #157676, this PR doesn't change PyTorch's behavior, but it fixes the translation layer, ensuring torch._numpy compatibility with NumPy. I am marking this PR as fixing #141563, even though PyTorch behavior isn't modified.
Notice that there are still some other bugs in PyTorch's advanced indexing, that need to be fixed (mainly regarding proper accounting of dimensions when multidimensional boolean masks are present). But those need to be fixed at the ATen operator level. Examples:
- #71673
- #107699
- #158125
Pull Request resolved: https://github.com/pytorch/pytorch/pull/158297
Approved by: https://github.com/soumith
Written with Claude Code.
Fixes https://github.com/pytorch/pytorch/issues/157569
Fixes https://github.com/pytorch/pytorch/issues/158134
NumPy and PyTorch handle advanced indexing differently when advanced indices are separated by slices (e.g., arr[:, [0], :, 0]). PyTorch uses "outer" indexing placing result dimensions in original positions, while NumPy uses "vectorized"
indexing moving advanced index dimensions to the front.
This adds _numpy_style_advanced_indexing() to detect separated advanced indices and transpose results to match NumPy's dimension ordering, ensuring torch._numpy maintains compatibility with NumPy's indexing behavior.
Fixes cases like:
- arr[:, [0], :, 0] now returns shape (1, 5, 7) instead of (5, 1, 7)
- arr[:, [0, 1], :, 0] now returns shape (2, 5, 7) instead of (5, 2, 7)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/157676
Approved by: https://github.com/manuelcandales
Co-authored-by: Claude <noreply@anthropic.com>
