Composite Tools Supports Default Return Values

[jerm-dro]

Summary

Composite tool steps can be skipped for a few reasons:

• an error occurs, but the composite tool is configured to continue on errors from the step: FailureMode: "continue"
• the step can be conditional: Condition: "false".

Problems / confusion arise when we depend on the output of a skipped step. The templating engine expands these missing values to "<no value>".

Proposed Solution

Hoisting a slightly modified version of @tgrunnagle's solution from one of the threads below:

We'd require a

step: {
    ...
    // a key value pair is required in defaultResults iff:
    // (the step is conditional OR failure mode is continue) 
    //  AND the key is referenced in downstream steps.
    defaultResults: {
        "some_returned_value_name": "default value for downstream"
    }
}

The defaultResults are used if the step is skipped for any reason.

Acceptance Criteria

• An integration tests demonstrating default results being used for both conditional and failureMode=continue steps.
• Unit tests for validation that assert an error is produced if a step may be skipped, its outputs are referenced downstream, and no defaults are configured.
• Documentation describing when and how to configure the defaultResults in the CRD for vMCP.

Relevant Links

• A prior discussion where potential solutions are discussed starts here
• Multiple discussions here highlighting confusing or incorrect behavior solved by configuring defaults.