Add contiguity check to try_as_slice() and contiguous() function

[ymote]

Summary

• Add is_contiguous() method to Array to check if the array has contiguous memory layout
• Add NotContiguous error variant to AsSliceError
• Update try_as_slice() to check contiguity before returning slice (BREAKING CHANGE)
• Add contiguous() function to ops module to make non-contiguous arrays contiguous

Motivation

Previously, as_slice() would return raw memory ignoring strides, causing silent data corruption when the array was not contiguous. This was a significant source of bugs when working with indexed or transposed arrays.

For example:

let arr = Array::from_slice(&[1i32, 2, 3, 4, 5, 6], &[2, 3]);
let transposed = ops::transpose(&arr)?;
let slice = transposed.as_slice::<i32>();  // WRONG DATA!

The slice would contain elements in the wrong order because transpose() creates a strided view, but as_slice() ignored the strides.

Changes

Array::is_contiguous()

Checks if the array is contiguous (row-major/C-style) by verifying strides match expected values.

AsSliceError::NotContiguous

New error variant returned when calling try_as_slice() on a non-contiguous array.

try_as_slice() update

Now checks contiguity after evaluation and returns NotContiguous error if the array is not contiguous.

ops::contiguous()

New function that returns a contiguous copy of the array if needed.

Migration Guide

If your code used as_slice() on indexed/transposed arrays, it was likely producing incorrect results. To fix:

// Option 1: Use contiguous()
let c = ops::contiguous(&arr)?;
let slice = c.as_slice::<f32>();

// Option 2: Reshape to force contiguity
let n = arr.size() as i32;
let c = arr.reshape(&[n])?.reshape(arr.shape())?;
let slice = c.as_slice::<f32>();

Test Plan

• Unit tests for is_contiguous() with various array shapes
• Unit tests for try_as_slice() returning NotContiguous error
• Unit tests for contiguous() function
• Verified fix in real-world use case (image generation pipeline that was producing tiled images due to this bug)

🤖 Generated with Claude Code

[dcvz]

@ymote this seems to do more than just what the title suggests