[http-client-csharp] Avoid sharing ParameterProvider instances across generated methods

[ArcturusZhang]

Problem

Some C# generator method builders reuse ParameterProvider instances across multiple generated methods. That makes it unsafe to update a parameter in place for one method because the mutation can leak into sibling methods that reuse the same parameter object.

This came up while investigating partial method signature customization. There are currently two timing paths:

• Early method builders can clone parameters before constructing the body.
• Late customization filtering must rename existing parameters in place because the body may already hold cached VariableExpression/declaration references from those exact ParameterProvider instances.

The distinction exists largely because parameter ownership is ambiguous.

Proposal

Generated methods should not share ParameterProvider instances. Each method should own its signature parameters, and body construction should use those method-owned parameter instances.

Advantages

• Partial method customization can use one simpler model: rename the method-owned parameters in place before or during final signature resolution.
• Renaming parameters becomes safer because changes cannot leak from one generated method to another.
• Default-value stripping for partial method implementations cannot accidentally affect sibling overloads.
• Method bodies, XML docs, validation, and invocation expressions all continue to reference the same parameter declarations.
• Downstream emitters do not need to know whether a customization happens before or after body construction.
• It reduces hidden coupling in method builders and makes future visitors/refactorings safer.

Related context

This was observed in the C# partial method customization flow, where cloned parameters are safe only before body construction, while late customization requires in-place renaming to keep body references valid.

[github-actions]

🎯 Issue Triage

This is a feature/refactoring proposal to eliminate shared ParameterProvider instances across generated C# methods to prevent mutation leakage and simplify partial method customization.

Category: Feature Request
Area: emitter:client:csharp

🔍 Analysis

• Root cause: Method builders in the C# generator reuse ParameterProvider instances across multiple generated methods, making in-place mutations (e.g., renaming) unsafe as changes leak into sibling methods.
• Impact: Affects partial method signature customization — early builders clone parameters (safe), but late customization must mutate in place (risky).
• Proposed fix: Each generated method owns its own ParameterProvider instances so renaming/mutation is always safe.
• Benefits: Simplifies customization model, removes hidden coupling, makes future refactors safer, no downstream emitter awareness of timing needed.
• No duplicates found.

📝 Suggested next steps

• Audit all method builders in the C# generator that share ParameterProvider instances.
• Ensure method construction always clones/owns parameters before body construction.
• Update partial method customization flow to rely on single in-place rename path.
• Add tests verifying that renaming a parameter in one method does not affect sibling overloads.

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