java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING when using non-object withItems

[crenshaw-dev]

To reproduce:

# Submit a workflow where withItems is an array of strings.
argo submit https://raw.githubusercontent.com/argoproj/argo/master/examples/loops-dag.yaml

# Grab my branch with the test modified to just list workflows.
git clone https://github.com/mac9416/argo-client-gen
cd argo-client-gen
git checkout withitems-bug

# Build and test.
make java
make test-java

You should receive the following error:

com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 758 path $.items[0].spec.templates[0].dag.tasks[1].withItems[0]
        at io.argoproj.workflow.SmokeIT.testArgoServerAPI(SmokeIT.java:39)

Ideally fixing argoproj/argo-workflows#2790 would fix this. But I suspect that bug will require using Swagger's oneOf feature, which it looks like openapi-generator does not yet support.

Assuming we can't find a swagger spec that satisfies openapi-generator, maybe the next best solution is to override withItems to be simply a list of objects. That would allow proper posting of workflows. It may even permit proper retrieval, assuming the client can cast to a known type.

To go that route, we'd probably want to create a named, synthetic type in swagger.json to represent the type of withItems. That would allow easily overriding the type by name in openapi-generator. If the type info were embedded directly in the withItems block, I'm not sure it could be overridden so easily.