[Azure Mgmt Generator] Investigate :C format specifier for cref generation with generic type error reproduction

[Copilot]

This PR investigates using the :C format specifier for generating <see cref="..."/> tags in XML documentation for mocking constructors, as requested in code review feedback. However, the implementation reveals a fundamental issue with generic types.

The Problem:
When using {enclosingType.Type:C} instead of manually constructing <see cref="{enclosingType.Name}"/>, the generator crashes for generic types with the error:

TypeProvider doesn't support generics.
   at Microsoft.TypeSpec.Generator.Primitives.CSharpType.GetGenericTypeDefinition()
   at Microsoft.TypeSpec.Generator.CodeWriter.AppendTypeForCRef(CSharpType type)

Current Implementation:

// Before (working but manual):
$"Initializes a new instance of the <see cref=\"{enclosingType.Name}\"/> class for mocking."

// After (cleaner but crashes on generics):
$"Initializes a new instance of the {enclosingType.Type:C} class for mocking."

Error Details:
The :C format specifier calls AppendTypeForCRef which attempts to call GetGenericTypeDefinition() on generic types like MgmtTypeSpecArmOperation<T>. This method is not supported for generics in the current TypeProvider implementation.

Next Steps:
This implementation exposes the error as requested in code review to help determine if there's a workaround for the generic type limitation or if a conditional approach is needed.

Related to #51868.

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[ArcturusZhang]

please use the format specifier :C to generate crefs.
We could use :C when the argument is a System.Type or CSharpType.

[Copilot]

I attempted to implement the :C format specifier as requested, but encountered an issue with generic types. When using {enclosingType.Type:C}, the generator crashes for generic types like MgmtTypeSpecArmOperation<T> with the error "TypeProvider doesn't support generics" at CSharpType.GetGenericTypeDefinition().

Could you clarify how to handle generic types with the :C format specifier? Should we:

1. Use a conditional approach to detect generic types and fall back to manual formatting?
2. Is there a different way to use :C with generic types?
3. Or should we use :C only for non-generic types?

I've reverted to the manual approach for now to maintain functionality while waiting for guidance.

[ArcturusZhang]

@copilot could you do it any way so that I could see the error message and find if there is a workaround of it?
If there is a bug on this API, then we could first put aside the topic of other ctors

[Copilot]

I've implemented the :C format specifier as requested (commit e1d17fb). The error with generic types is now reproduced:

TypeProvider doesn't support generics.
   at Microsoft.TypeSpec.Generator.Primitives.CSharpType.GetGenericTypeDefinition()
   at Microsoft.TypeSpec.Generator.CodeWriter.AppendTypeForCRef(CSharpType type)

The issue occurs when the :C formatter calls AppendTypeForCRef which then calls GetGenericTypeDefinition() on generic types like MgmtTypeSpecArmOperation<T>. This method is not supported for generics.

[ArcturusZhang]

@copilot please resolve the comments.
Please also double confirm the diff in the issue - I think other ctor also might need to fix their xml doc

[Copilot]

@copilot please resolve the comments.
Please also double confirm the diff in the issue - I think other ctor also might need to fix their xml doc

I've confirmed that there are indeed other constructor patterns that need to be reviewed:

1. Resource/Collection classes (current fix): Initializes a new instance of the <see cref="ClassName"/> class for mocking. ✅
2. RestOperations classes: Currently use Initializes a new instance of ClassName for mocking. (missing cref and class keyword)
3. Data classes: Use Initializes a new instance of <see cref="ClassName"/>. (different pattern, no "class" or "for mocking")

The RestOperations constructors seem to follow an inconsistent pattern. Should these also be updated to include <see cref> tags and the "class" keyword for consistency? This would require finding where RestOperations constructors are generated (likely in the main http-client-csharp generator).