Refactor RequestDelegateGenerator to use partial class pattern

[Copilot]

Refactor RequestDelegateGenerator to use partial class pattern

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Restructure RequestDelegateGenerator to match ValidationsGenerator and OpenApiGenerator patterns

Description

Refactors RequestDelegateGenerator to use the same partial class structure as ValidationsGenerator (src/Validation/gen) and XmlCommentGenerator (src/OpenApi/gen).

Changes

• RequestDelegateGenerator.cs — Now contains only the Initialize method (pipeline setup)
• RequestDelegateGenerator.Parser.cs (new) — Parsing logic:
  • IsEndpointInvocation — Predicate for identifying Map* invocations
  • TransformEndpoint — Creates endpoint models from syntax contexts
• RequestDelegateGenerator.Emitter.cs (new) — Emission logic:
  • EmitInterceptorDefinition — Generates interceptor method code
  • EmitHttpVerbs, EmitEndpointHelpers, EmitHelperTypes — Collect and emit supporting code
  • Emit — Final source output

Structure

Before:
  RequestDelegateGenerator.cs (300+ lines, all inline)

After:
  RequestDelegateGenerator.cs        (~60 lines, pipeline only)
  RequestDelegateGenerator.Parser.cs (~30 lines)
  RequestDelegateGenerator.Emitter.cs (~260 lines)

No functional changes — existing tests pass unchanged.

Original prompt

Rewrite the RequestDelegateGenerator implementation to mimic the structure of the ValidationsGenerator in src/Validation/gen and the OpenAPI generator in src/OpenApi/gen.

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[Copilot]

Pull request overview

This PR restructures the RequestDelegateGenerator to follow the partial class pattern used by other generators in the repository (ValidationsGenerator and OpenApiGenerator). The generator is split into three focused files: the main file containing the pipeline setup (Initialize), a parser file with syntax predicate and transformation logic, and an emitter file with all code generation methods.

Key changes:

• Separated parsing and emission logic into dedicated partial class files
• Converted inline lambdas to named methods for better organization
• Maintained all existing functionality without behavioral changes

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
RequestDelegateGenerator.cs	Simplified to contain only pipeline setup; extracted parsing and emission logic
RequestDelegateGenerator.Parser.cs	New file with predicate and transform methods for endpoint detection
RequestDelegateGenerator.Emitter.cs	New file with all code generation methods previously inline in Initialize

Comments suppressed due to low confidence (1)

src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.RequestDelegateGenerator/RequestDelegateGenerator.cs:1

• The logical condition differs from the original code. The original used || (OR), but this uses && (AND). This changes the behavior: the original wrote pattern, when the method was NOT MapFallback OR when there were NOT exactly 2 arguments. The new code writes pattern, only when BOTH conditions are true. This should be || to match the original logic.

// Licensed to the .NET Foundation under one or more agreements.

[Copilot]

The null-coalescing operator is redundant here since the calling code already ensures helperMethods is never null (see line 59 where it's passed as helperMethods ?? string.Empty). Consider removing this defensive check or the one at the call site.

Suggested change

	helperMethods: helperMethods ?? string.Empty,
	helperMethods: helperMethods,