Multiple RegisterOrReplace calls for the same pipeline step identifier throws System.Exception: Step registration with id '<step-identifier>' is already registered for '<step-identifier>'.

[ngallegos]

Describe the bug

Symptoms

When calling RegisterOrReplace more than once for the same pipeline step identifier, an exception in the following format is thrown:

System.Exception: Step registration with id '<step-identifier>' is already registered for '<step-identifier>'.

Who's affected

Anyone with a use case for calling RegisterOrReplace on the same pipeline step more than once. One such use case is described in this Discourse post.

Root cause

The call to RegisterOrReplace adds a RegisterOrReplaceStep to a list that is processed when the pipeline model is built without any checking for duplicates. As a result, the same logic that prevents more than one Register step with the same StepId throws an exception when duplicate steps are found.

Confirmed workarounds

None

Original bug report

From the following Discourse post:
https://discuss.particular.net/t/multiple-registerorreplace-calls-for-same-pipeline-step-identifier/4468

We have multiple pipeline steps that are added depending on certain criteria. It might happen that the exact same behavior has already been registered (because of some shared logic). Therefore, I wanted to use the RegisterOrReplace hook. My understanding was that it would either replace an existing step of the same identifier, or do its actual registration.

When I do the following:

pipeline.RegisterOrReplace(
    stepId: nameof(DemoPipelineStep),
    behavior: new DemoPipelineStep(),
    description: "test");

// somewhere later on
pipeline.RegisterOrReplace(
    stepId: nameof(DemoPipelineStep),
    behavior: new DemoPipelineStep(),
    description: "test");

This crashes with System.Exception: Step registration with id 'DemoPipelineStep' is already registered for 'Demo.DemoPipelineStep'.

It only works if one of the two registration steps uses the Register hook, the actual order of registration has no impact.
My understanding of RegisterOrReplace would have been that it simply does not matter how often I call RegisterOrReplace with the same step identifier, the last registration that is called would win and do the replacement. Is this intended behavior?

Steps to reproduce

Register or replace the same pipeline step using the RegisterOrReplace method more than once, and try to run the project.

Relevant log output

Additional Information

None