[Storage] Newly changed `list_blobs` API unexpected failure (against `v0.25` of `typespec-rust`)

[vincenttran-msft]

Relevant code can be found in this PR: #3284 (this issue was identified when working on an unrelated feature).

When generating against v0.25 of typespec-rust emitter package version, it seems that pageable operations now return a Pager rather than a PageIterator. For example:

// Old
pub fn list_blob_flat_segment(
        &self,
        options: Option<BlobContainerClientListBlobFlatSegmentOptions<'_>>,
    ) -> Result<PageIterator<Response<ListBlobsFlatSegmentResponse, XmlFormat>>> {

// New
pub fn list_blob_flat_segment(
        &self,
        options: Option<BlobContainerClientListBlobFlatSegmentOptions<'_>>,
    ) -> Result<Pager<ListBlobsFlatSegmentResponse>> {

Our test code does the following:

1. Create a test container
2. Create 2 test blobs, upload them
3. Call list_blobs simplest form, no options
4. Work with the return type to do a simple assertion against the blobs returned

Attached below is our old code and against the newly refactored code:

// Old (against PageIterator)
let mut list_blobs_response = container_client.list_blobs(None)?;

    let page = list_blobs_response.try_next().await?;
    let list_blob_segment_response = page.unwrap().into_body()?;
    let blob_list = list_blob_segment_response.segment.blob_items;
    for blob in blob_list {
        let blob_name = blob.name.unwrap().content.unwrap();
        let properties = blob.properties.unwrap();
        let blob_type = properties.blob_type.unwrap();
        let etag = properties.etag;
        assert!(blob_names.contains(&blob_name));
        assert_eq!(BlobType::BlockBlob, blob_type);
        assert!(etag.is_some());
    }

// New (against Pager)
let mut list_blobs_response = container_client.list_blobs(None)?;
while let Some(blob_result) = list_blobs_response.next().await {
        let blob = blob_result?;
        let blob_name = blob.name.unwrap().content.unwrap();
        let properties = blob.properties.unwrap();
        let blob_type = properties.blob_type.unwrap();
        let etag = properties.etag;
        assert!(blob_names.contains(&blob_name));
        assert_eq!(BlobType::BlockBlob, blob_type);
        assert!(etag.is_some());
    }

Could you advise how to deal with this error we are facing?

Error: Error { context: Custom(Custom { kind: DataConversion, error: Error("expected value", line: 1, column: 1) }) }

This break occurs in multiple places (all of our list blobs across the different client types, the perf-testing, etc.). Thanks!

Note: For sanity, the XML body is coming back correctly when observing in Fiddler, so it seems like the break is how we process the response.

[jhendrixMSFT]

This is a codegen bug. Missing XmlFormat on the Pager definition.

[jhendrixMSFT]

The fix will be in emitter version v0.26.0.