Fix return type diagnostic conditions

[Dreamescaper]

No description provided.

[Copilot]

Pull Request Overview

This PR updates the return-type validation for CustomHandler methods by broadening the condition and aligning the diagnostic message.

• Refactored the diagnostic message to reference the “first parameter” instead of “‘this’ parameter”
• Removed the extension-method-only guard in the return-type check
• Aligned the generator logic to always validate non-void return types against the first parameter

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
ServiceScan.SourceGenerator/DiagnosticDescriptors.cs	Updated the WrongReturnTypeForCustomHandler message to refer to “first parameter type.”
ServiceScan.SourceGenerator/DependencyInjectionGenerator.ParseMethodModel.cs	Removed the method.IsExtensionMethod check so the return-type diagnostic applies universally.

Comments suppressed due to low confidence (3)

ServiceScan.SourceGenerator/DiagnosticDescriptors.cs:58

• [nitpick] The diagnostic message could be more precise by saying “type of its first parameter,” for example: "Method with CustomHandler must return void or the type of its first parameter".

"Method with CustomHandler must return void or first parameter type",

ServiceScan.SourceGenerator/DependencyInjectionGenerator.ParseMethodModel.cs:87

• Add unit tests for CustomHandler methods to verify behavior both when they are extension methods and when they are not, ensuring the new return-type logic works as intended.

if (!method.ReturnsVoid &&

ServiceScan.SourceGenerator/DependencyInjectionGenerator.ParseMethodModel.cs:87

• Dropping the IsExtensionMethod guard makes this check fire on all methods, which may incorrectly flag non-extension CustomHandler methods. Consider scoping it back to extension methods or explicitly attributed handlers.

if (!method.ReturnsVoid &&