[tcgc] namespaces in TCGC

[iscai-msft]

Clear and concise description of the problem

As we start implementing "namespace is namespace" in our language emitters, TCGC plays an important role in helping emitters get the information they need to generate. At the same time, it is important that we are not breaking, both for ease of migration, and also because some languages (like javascript) don't really have a concept of "namespace" and won't be adopting this behavior the same way the other language emitters are.

As such, I propose a multi-part approach in getting TCGC to help with the "namespace is namespace" push.

1. Ensure that the existing .namespace string on SdkClientTypes returns the correct namespace
2. Add a .namespace string onto SdkModelType and SdkEnumType, so we can generate these models in the correct space.
3. Add additional helper method getNamespaceToClients(sdkContext) that returns a mapping of namespaces to clients in those namespaces.
4. Add additional helper method getNamespaceToModels(sdkContext) that will return a mapping of namespaces to models in those namespaces

Checklist

• Follow our Code of Conduct
• Check that this issue is about the Azure libraries for typespec. For feature request in the typespec language or core libraries file it in the TypeSpec repo
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[tadelesh]

Another option is making SkdPackage to be hierarchy with namespace, and add a flag like flatten-namespace and default to true to prevent breaking change for some languages.

[chunyu3]

How about the namespace defined in @client? As following, the client include more parts separated by ., and all the parts except the latest one will be the namespace of the client, will tcgc help to merge this to namespace of the client?

@client(
  {
    name: "SubNamespace.SecondClient",
    service: FirstTest.Service,
  }
)

[archerzz]

For 3 & 4, what's the user scenario? There are basically 2 ways to provide the relationship between the namespaces and their belonging entities (clients, models, etc):

• a hierarchy of SdkInputNameSpace with child properties representing clients, models, etc.
• or a flat mapping like suggested on top