Autorest python failing for x-ms-pageable extension while passing for CSharp

Input Json: https://github.com/Azure/azure-rest-api-specs/blob/master/arm-recoveryservicesbackup/2016-12-01/swagger/backupManagement.json Autorest version: 1.0.1-20170517-2300-nightly

Failure error:

FATAL: System.Collections.Generic.KeyNotFoundException: Couldn't find the item property specified by extension
   at AutoRest.Python.Azure.TransformerPya.GetPagingSetting(CodeModelPya codeModel, CompositeType body, Dictionary`2 extensions, String valueTypeName, IDictionary`2 typePageClasses, String methodName)
   at AutoRest.Python.Azure.TransformerPya.NormalizePaginatedMethods(CodeModelPya codeModel)
   at AutoRest.Python.Azure.TransformerPya.TransformCodeModel(CodeModel cm)
   at Generator.<ProcessInternal>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at NewPlugin.<Process>d__11.MoveNext()
FATAL: python/generate - FAILED
Process() Cancelled due to exception : Plugin python reported failure.
Error: Plugin python reported failure.
    at C:\Users\dhratho\.autorest\plugins\autorest\1.0.1-20170517-2300-nightly\node_modules\autorest-core\lib\pipeline\pipeline.js:88:19
    at next (native)
    at fulfilled (C:\Users\dhratho\AppData\Roaming\npm\node_modules\autorest\lib\polyfill.min.js:10:59)
    at process._tickCallback (internal/process/next_tick.js:109:7)

This error is coming for Python generator while working fine for CSharp generator.

Diagnostics:

• In paths with operation_id Operations_List, response schema name is ClientDiscoveryResponse which is pageable and hence NextLink and Value fields are present in schema.
• In schema properties NextLink and Value are present, but python generator is looking for “value” field which is not present and hence failing. (Autorest.Python.Azure TransformerPya.cs#129).
• But on the other hand in CSharp generator (Autorest.CSharp.Azure TransformerCsa.cs#184 GetPagingSetting) no such check is present.
• On further analysis it turns out that this check is present only in Python generator, which presents inconsistency across generator transformers.

[olydis]

Shouldn’t be a linter rule that check itemName content or value is in the Swagger?

excellent idea, I’ll file an issue!

[DheerendraRathor]

@olydis C# generator doesn’t check whether property with itemName actually exists. Surprising thing is only Python generator is making this check and even Python generator is missing check for nextLinkName (though code exists, it is just not enforcing check).

I believe python is making these checks as in-built json module in python is case sensitive.

Although this can be made consistent across languages by adding these checks appropriately.