Validate ScatterND index depth

[Akshay Sonawane (apsonawane)]

This pull request improves input validation for the ScatterND operator and adds a corresponding unit test to ensure that invalid input is properly rejected.

Input validation:

• Added a check in scatter_nd.h to ensure that the last dimension of the indices tensor is at least 1, returning an error if it is not.

Testing:

• Added a unit test in scatter_nd_op_test.cc (ScatterND_rejects_zero_index_depth) to verify that the operator rejects indices tensors with a zero-sized last dimension.

[Copilot]

Pull request overview

This pull request strengthens runtime input validation for the CPU ScatterND operator by rejecting indices tensors whose last dimension (index depth) is zero, and adds a unit test to ensure that invalid case is properly rejected.

Changes:

• Add ValidateShapes guard to require indices.shape[-1] >= 1, returning INVALID_ARGUMENT otherwise.
• Add a unit test that constructs indices with shape {1, 0} and asserts the operator fails with the expected error substring.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
onnxruntime/core/providers/cpu/tensor/scatter_nd.h	Adds a shape-validation check to reject zero (or negative) index depth in indices.
onnxruntime/test/providers/cpu/tensor/scatter_nd_op_test.cc	Adds a regression test ensuring the new validation triggers for {1, 0} indices.

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[Ti-Tai Wang (titaiwangms)]

Major review finding

onnxruntime/core/providers/cpu/tensor/scatter_nd.h:34

This rejects indices.shape[-1] == 0, but the ONNX ScatterND contract only requires the tuple length k to be at most rank(data) and defines updates.shape = indices.shape[:-1] ++ data.shape[k:]. It does not impose a lower bound of 1.

For example, data=[2,3], indices=[1,0], and updates=[1,2,3] represent one empty index tuple updating the entire tensor. The new validation rejects this contract-valid model across every provider using the shared helper.

Please handle k == 0 safely rather than declaring it invalid.