[DPG] Can't generate with @pagedResult models

[catalinaperalta]

I have the following typespec specification: https://github.com/Azure/azure-rest-api-specs/tree/feature/blob-tsp/specification/storage/Microsoft.BlobStorage

When I try to generate using the typespec-python emitter, I get the following error:

NOTE: I still see this issue with typespec-python 0.36.1.

PS C:\Users\caperal\repos\azure-rest-api-specs\specification\storage\Microsoft.BlobStorage> tsp compile .\client.tsp --emit @azure-tools/typespec-python
TypeSpec compiler v0.61.2

Traceback (most recent call last):
  File "C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python/eng/scripts/setup/run_tsp.py", line 40, in <module>
    preprocess.PreProcessPlugin(output_folder=args.output_folder, cadl_file=args.cadl_file, **unknown_args).process()
  File "C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python\generator\pygen\__init__.py", line 93, in process
    self.update_yaml(yaml_data)
  File "C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python\generator\pygen\preprocess\__init__.py", line 503, in update_yaml
    self.update_operation_groups(yaml_data, client)
  File "C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python\generator\pygen\preprocess\__init__.py", line 492, in update_operation_groups
    self.get_operation_updater(operation)(code_model, operation)
  File "C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python\generator\pygen\preprocess\__init__.py", line 461, in update_paging_operation
    item_type = item_type or yaml_data["itemType"]["elementType"]
                             ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
KeyError: 'elementType'
Emitter "@azure-tools/typespec-python" crashed! This is a bug.
Please file an issue at https://github.com/Azure/autorest.python/issues

Error: Command failed: C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python\venv\Scripts\python.exe C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python/eng/scripts/setup/run_tsp.py --output-folder=C:/Users/caperal/repos/azure-rest-api-specs/specification/storage/Microsoft.BlobStorage/tsp-output/@azure-tools/typespec-python --cadl-file=C:/Users/caperal/AppData/Local/Temp/cadl-codegen/python-yaml-pathd263dee7-3893-4099-994b-0134b88c2fc0.yaml --package-version=1.0.0b1 --generate-packaging-files=true --flavor=azure --package-dir=azure-storage-blob --package-name=azure-storage-blob --package-mode=azure-dataplane --models-mode=dpg --emit-cross-language-definition-file=true --from-typespec=true
Traceback (most recent call last):
  File "C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python/eng/scripts/setup/run_tsp.py", line 40, in <module>
    preprocess.PreProcessPlugin(output_folder=args.output_folder, cadl_file=args.cadl_file, **unknown_args).process()        
  File "C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python\generator\pygen\__init__.py", line 93, in process
    self.update_yaml(yaml_data)
  File "C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python\generator\pygen\preprocess\__init__.py", line 503, in update_yaml
    self.update_operation_groups(yaml_data, client)
  File "C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python\generator\pygen\preprocess\__init__.py", line 492, in update_operation_groups
    self.get_operation_updater(operation)(code_model, operation)
  File "C:\Users\caperal\repos\azure-rest-api-specs\node_modules\@typespec\http-client-python\generator\pygen\preprocess\__init__.py", line 461, in update_paging_operation
    item_type = item_type or yaml_data["itemType"]["elementType"]
                             ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
KeyError: 'elementType'

    at checkExecSyncError (node:child_process:890:11)
    at execSync (node:child_process:962:15)
    at $onEmit (file:///C:/Users/caperal/repos/azure-rest-api-specs/node_modules/@typespec/http-client-python/dist/emitter/emitter.js:101:9)
    at async Object.$onEmit [as emitFunction] (file:///C:/Users/caperal/repos/azure-rest-api-specs/node_modules/@azure-tools/typespec-python/dist/src/emitter.js:3:5)
    at async runEmitter (file:///C:/Users/caperal/repos/azure-rest-api-specs/node_modules/@typespec/compiler/dist/src/core/program.js:367:13)
    at async compile (file:///C:/Users/caperal/repos/azure-rest-api-specs/node_modules/@typespec/compiler/dist/src/core/program.js:119:9)
    at async compileOnce (file:///C:/Users/caperal/repos/azure-rest-api-specs/node_modules/@typespec/compiler/dist/src/core/cli/actions/compile/compile.js:36:25)
    at async compileAction (file:///C:/Users/caperal/repos/azure-rest-api-specs/node_modules/@typespec/compiler/dist/src/core/cli/actions/compile/compile.js:19:9)

--------------------------------------------------
Library Version                0.35.1
TypeSpec Compiler Version      0.61.2
--------------------------------------------------

Workaround: Had to comment out the @pagedResult decorator in order to be able to get something generated which means the generated code is wrong.

[msyyc]

@catalinaperalta Maybe it is because you don't define Azure.Core.Items in return type of paging operation. Here is an example: https://github.com/Azure/cadl-ranch/blob/0bbcb24a30dff529be1a0bb69623237040e9d55b/packages/cadl-ranch-specs/http/azure/core/page/main.tsp#L138-L148

[catalinaperalta]

This is for a brownfield service that isnt following current guidance, here are some examples of the response models:

• https://github.com/Azure/azure-rest-api-specs/blob/8e0d1c458295044b3119a335f0500461039a9745/specification/storage/Microsoft.BlobStorage/models.tsp#L895-L906
• https://github.com/Azure/azure-rest-api-specs/blob/8e0d1c458295044b3119a335f0500461039a9745/specification/storage/Microsoft.BlobStorage/models.tsp#L167-L193

What are we using the items for? The return signature?