[Validation] Support generated ValidatableTypeAttribute for Blazor

[javiercn]

The ValidationsGenerator now supports discovering types marked with ValidatableTypeAttribute from two sources:

Framework attribute: Microsoft.Extensions.Validation.ValidatableTypeAttribute (from Microsoft.Extensions.Validation package)
SDK-generated attribute: Microsoft.Extensions.Validation.Embedded.ValidatableTypeAttribute (embedded by Razor SDK in projects with .razor files)
This enables developers to use [ValidatableType] in Blazor projects without explicitly referencing the experimental validation framework attribute, as the Razor SDK automatically embeds the attribute as needed on the assembly

[Copilot]

Pull Request Overview

This PR adds support for generated ValidatableTypeAttribute to work alongside the existing framework version in Blazor scenarios. The main purpose is to enable validation generators to recognize and process both the framework-provided ValidatableTypeAttribute and a generated version that can be provided by the Razor SDK.

Key Changes

• Modified the validation generator to process both framework and generated versions of ValidatableTypeAttribute
• Added test snapshots demonstrating the generated code output for auto-generated attributes
• Created comprehensive test cases covering scenarios with both attribute types

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

File	Description
ValidationsGenerator.cs	Modified to collect and combine validatable types from both framework and generated attributes
ValidationsGenerator.AttributeParser.cs	Updated parameter names to follow discard pattern conventions
ValidationsGenerator.AutoGeneratedAttribute.cs	Added test cases for discovering and using generated ValidatableTypeAttribute
Snapshot files (3)	Test verification snapshots for generated code output

[captainsafia]

This namespace looks incorrect. Is it because the source strings in the test code use file-scoped namespaces? 🤔

[javiercn]

I regenerated the tests. For some reason the tests were passing but nothing was happening. I even introduced a compilation issue on purpose to make them fail and were green.

I switched to use the old style namespaces and Program main and that got them "working" again

[oroztocil]

@javiercn

1. Is there a complementary PR that adds emitting the attribute into projects?
2. Does this mean that you get access to the generated attribute only in Razor SDK based projects? I.e. you can't have models in a (non-Razor) class library?

[javiercn]

@javiercn

1. Is there a complementary PR that adds emitting the attribute into projects?
2. Does this mean that you get access to the generated attribute only in Razor SDK based projects? I.e. you can't have models in a (non-Razor) class library?

dotnet/sdk#50083 <- Complementary PR for emitting the attribute.

2. Does this mean that you get access to the generated attribute only in Razor SDK based projects? I.e. you can't have models in a (non-Razor) class library?

Yep, but that's not a big deal. Referencing the Razor SDK is not a problem and the embedded (I'm going to start calling it like that) is a thing only for .net 10.0, we plan to move out of it once the other attribute stabilizes.