Fix ValidationsGenerator CS8785 when AddValidation is called from multiple sites

[Copilot]

ValidationsGenerator threw CS8785 and discarded all generated output whenever AddValidation() appeared more than once in a project. The root cause: CreateSyntaxProvider returns an IncrementalValuesProvider<T> (one item per call site), so .Combine(validatableTypes) + RegisterSourceOutput fired once per call site — each attempting to AddSource("ValidatableInfoResolver.g.cs", ...), which is illegal.

Description

• ValidationsGenerator.cs: Call .Collect() on the addValidation provider before .Combine(validatableTypes), collapsing all call sites into a single ImmutableArray so RegisterSourceOutput fires exactly once.
• ValidationsGenerator.Emitter.cs: Update Emit to accept ImmutableArray<InterceptableLocation?>, filter nulls using .OfType<InterceptableLocation>(), bail if empty, and emit one [InterceptsLocation] attribute per call site on the single interceptor method (already declared AllowMultiple = true).
• Regression test: CanGenerateWhenAddValidationCalledMultipleTimes — two consecutive AddValidation() calls still produce a single ValidatableInfoResolver.g.cs with two [InterceptsLocation] attributes, and the endpoint correctly returns HTTP 400 for invalid input.
• Test infrastructure fix: Added System.ComponentModel.Primitives assembly reference to ValidationsGeneratorTestBase so the generator can resolve System.ComponentModel.DisplayNameAttribute during tests (required by the DisplayNameInfo support added in the main branch).

// Previously caused CS8785 — generator output silently discarded, endpoints never validated
builder.Services.AddValidation();
builder.Services.AddValidation();

[Copilot]

Pull request overview

This PR fixes the ValidationsGenerator emitting duplicate sources (triggering CS8785 and discarding output) when AddValidation() is invoked multiple times in a project, by collapsing multiple call sites into a single emission and generating multiple [InterceptsLocation] attributes on the interceptor.

Changes:

• Collect AddValidation call sites before combining with discovered validatable types so RegisterSourceOutput runs once.
• Update the emitter to accept multiple interceptable locations and emit one interceptor method annotated for each call site.
• Add a regression test and verified snapshot covering multiple AddValidation() invocations.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/Validation/gen/ValidationsGenerator.cs	Collects all AddValidation call sites before combining with validatable types to prevent duplicate hint-name emissions.
src/Validation/gen/Emitters/ValidationsGenerator.Emitter.cs	Emits multiple [InterceptsLocation] attributes for a single generated interceptor when multiple call sites exist.
src/Validation/test/Microsoft.Extensions.Validation.GeneratorTests/ValidationsGenerator.NoOp.cs	Adds regression test validating multiple AddValidation() calls still result in request validation (HTTP 400 on invalid payload).
src/Validation/test/Microsoft.Extensions.Validation.GeneratorTests/snapshots/ValidationsGeneratorTests.CanGenerateWhenAddValidationCalledMultipleTimes#ValidatableInfoResolver.g.verified.cs	Updates verified generator output to include multiple interceptor attributes for multiple call sites.

[oroztocil]

Looks good. I'll leave it up to you if you want to apply the nit suggestions for null filtering.

[Youssef1313]

@copilot CanGenerateWhenAddValidationCalledMultipleTimes is failing. Update the test to pass.

[Copilot]

@copilot CanGenerateWhenAddValidationCalledMultipleTimes is failing. Update the test to pass.

Fixed in dc82b23. The failure had two causes from the main branch merge: (1) the generator now looks up System.ComponentModel.DisplayNameAttribute via WellKnownTypes.Get (throws if missing), but System.ComponentModel.Primitives.dll wasn't in the test compilation's references — added MetadataReference.CreateFromFile(typeof(System.ComponentModel.DisplayNameAttribute).Assembly.Location) to ValidationsGeneratorTestBase; (2) the generator's emitter changed its output format (now uses displayNameInfo instead of displayName) — updated the snapshot accordingly.