[Bug] FunctionMetadataGenerator does not assign cardinality as many for IEnumerable<> scenarios

[surgupta-msft]

Investigate and fix in FunctionMetadataGenerator and Source Generation why Cardinality is not assigned to Many when function binds to IEnumerable<> type. This stops the collection support even when it is enabled by the extension - here as Host uses the value of cardinality to assign array type.

• Investigate/fix cardinality behavior in FunctionMetadataGenerator #1254
• Investigate/fix cardinality behavior in Source Generation #1255

Sample function for repro -

[Function("Function")]
public HttpResponseData Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", "post")] HttpRequestData req,
    [BlobInput("input-container", Connection = "AzureWebJobsStorage")] IEnumerable<string> blobs)
}

Current output function.metadata -

  "bindings": [
      {
        "name": "data",
        "type": "blob",
        "direction": "In",
        "blobPath": "input-container",
        "connection": "AzureWebJobsStorage"
       // "cardinality": "Many" --> Expected here
      },
      {
        "name": "$return",
        "type": "http",
        "direction": "Out"
      }
    ]

[satvu]

From a quick skim it seems we have handling and tests cases for Cardinality with EventHubs bindings but not Blobs ... from offline discussion we may also need handling for CosmosDB.

References that may help with investigation/fix:

1. What is officially supported according to storage extension docs.
2. We have the test case for this scenario with EventHubs bindings here which is run in the test matrix here.

[surgupta-msft]

Found some information in blob extension documentation. This can probably be the list of scenarios expected to be supported by this extension.

Another thing I found which may be helpful with the investigation here is isBatched = true for EventHubTrigger but not for KafkaTrigger and ServiceBus and they all implement ISupportCardinality. This can be the reason for why it works for only EventHubs

1. EventHubTriggerAttribute

 public sealed class EventHubTriggerAttribute : TriggerBindingAttribute, ISupportCardinality
    {
        // Batch by default
        private bool _isBatched = true;

2. KafkaTriggerAttribute

 public sealed class KafkaTriggerAttribute : TriggerBindingAttribute, ISupportCardinality
    {
        private bool _isBatched = false;