Expressions should have a conditional operator or function

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Expressions should have a way to write a condition. This could either be a ternary operator <condition> ? <true value> : <false value> or a function if(<condition>, <true-value>, <false-value>).

Original issue: actions/runner#409

[axel-h]

In addition, the solution should support non-trivial use cases, Which breaks down into:

• handling multiple values for one expression
• an if-cascade

Since expressions are supposed to be reasonable simple, there is no need for a sophisticated solution. But some syntactical sugar would be nice.

[piotrekkr]

There seems to be a way because there is "ternary like" operator in Github actions https://docs.github.com/en/actions/learn-github-actions/expressions#example . One thing to watch for is that "true value" (one after &&) need to be "truthy" to work as expected

${{ github.event_name == 'release' && github.ref || inputs.release_ref }}

[axel-h]

This is well known, but considered a poor solution due to the side effects. A real ternary operator is needed.

[piotrekkr]

Okay. Then probably title/description need to be updated to emphasize on being a real ternary and not this "kind of" ternary that already is there.

[davetapley]

Following the docs I just wrote this (legacy is a bool):

${{ (matrix.legacy && '') || '.new' }}.example.com

Can you spot the problem? I didn't at first:

'' is falsy, and so it falls through to '.new' regardless of the value of legacy, causing upload-artifact to fail with:

Error: Failed to CreateArtifact: Received non-retryable error: Failed request: (409) Conflict: an artifact with this name already exists on the workflow run

Very confusing at first, and a 'real' ternary if would have avoided it.

[TrongBYM]

Hello, was wondering if you found a workaround for this specific case?

[davetapley]

@TrongBYM yeah I just inverted the conditional:

${{ (!matrix.legacy && '.new') || '' }}.example.com

Not pretty but it works.

[salilsub]

Hi everyone, we just announced our new case function which is adds conditionals for expressions. Let us know if you have any feedback!