Canonicalize external data locations

[Akshay Sonawane (apsonawane)]

This pull request improves the robustness and correctness of handling external data references in ONNX Runtime, particularly focusing on rejecting invalid or ambiguous "location" entries and ensuring in-memory reference tags are not treated as file paths. The changes also enhance path validation logic and add new unit tests to cover these scenarios.

Validation and error handling improvements:

• Added a check in ExternalDataInfo::Create to reject duplicate "location" entries in the external data info, ensuring only one "location" is allowed per tensor. [1] [2]
• Updated path validation logic in ValidateExternalDataPathFromDir and ValidateExternalDataPath to explicitly reject in-memory reference tags (used for internal memory mapping) as invalid file paths, alongside empty and absolute paths. [1] [2] [3] [4] [5] [6]

Functionality and code clarity:

• Refined HasExternalDataInMemory to correctly detect in-memory references even if there are multiple "location" entries, improving reliability.

Testing enhancements:

• Added new unit tests to verify that duplicate "location" entries are rejected and that in-memory reference tags are correctly handled and rejected by validation logic. [1] [2]

These changes collectively strengthen the validation of external data references, prevent ambiguous or invalid configurations, and ensure that in-memory tags are never misinterpreted as file paths.

[Copilot]

Pull request overview

Strengthens external tensor-data handling by rejecting ambiguous locations and preventing internal memory tags from being interpreted as file paths.

Changes:

• Rejects duplicate or empty external-data locations.
• Detects memory tags across all location entries.
• Adds path-validation and parsing tests.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
onnxruntime/core/framework/tensor_external_data_info.cc	Validates location uniqueness and non-emptiness.
onnxruntime/core/framework/tensorprotoutils.cc	Improves memory-tag detection and path rejection.
onnxruntime/test/framework/tensorutils_test.cc	Covers duplicate locations and memory-tag validation.

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