Fix plugin EP test failure when host ORT lacks newer data types

[tianleiwu]

Description

Fix the CUDA plugin EP package test pipeline failure where the plugin is built with the latest code (which includes float8e8m0 and other newer data types), but the host ORT 1.26 release does not support these types. When the plugin attempts to register kernel type constraints containing unsupported types, GetTensorDataType fails and the plugin load crashes.

Motivation and Context

The plugin EP architecture allows plugins to be built against a newer version of the ONNX Runtime headers while being loaded into an older host ORT. However, the existing KernelDefBuilder::TypeConstraint methods call GetTensorType (which throws on unsupported types), making it impossible for a forward-compatible plugin to register kernels that include newer data types in their type constraint lists.

Changes

• Add TryGetTensorType() — a non-throwing variant of GetTensorType() that returns nullptr when the host ORT does not recognize a tensor element type.
• Add TryMLDataTypeToOrtDataType() — a non-throwing variant of MLDataTypeToOrtDataType() that returns nullptr instead of asserting/throwing.
• Update KernelDefBuilder::TypeConstraint (both vector and single-type overloads) to use the Try variants and gracefully skip unsupported types rather than failing.

Impact

• Plugins built with newer headers can now load into older host ORT releases without crashing on unknown data types.
• If all types in a constraint list are unsupported, the constraint is simply not registered (the kernel will not match, which is the correct fallback behavior).
• No behavioral change when the host supports all types — the code path is identical to before.

[Copilot]

Pull request overview

This PR aims to make plugin Execution Providers forward-compatible when built against newer ONNX Runtime headers but loaded into an older host ORT that lacks newly added tensor element types (e.g., float8 variants). It does so by introducing non-throwing type-conversion helpers and changing kernel type-constraint registration to skip types the host does not recognize.

Changes:

• Add TryGetTensorType() as a non-throwing variant of GetTensorType() that returns nullptr on failure.
• Add TryMLDataTypeToOrtDataType() as a non-throwing variant of MLDataTypeToOrtDataType() that returns nullptr when conversion isn’t possible.
• Update KernelDefBuilder::TypeConstraint overloads to use the Try* helpers and omit unsupported types.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

[sanaa-hamel-microsoft]

Mildly irked by the duplication in (Try)?MLDataTypeToOrtDataType, but should be fine.