Fix ValidationsGenerator CS8785 when AddValidation is called from multiple sites (#66675)

* Initial plan

* Fix ValidationsGenerator CS8785 when AddValidation is called multiple times

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Co-authored-by: Youssef1313 <31348972+Youssef1313@users.noreply.github.com>

* Small adjustments

* Update ValidationsGenerator.Emitter.cs

* Address review comment

* Address review comment

* Fix CanGenerateWhenAddValidationCalledMultipleTimes test: add System.ComponentModel.Primitives reference and update snapshot

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---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Youssef1313 <31348972+Youssef1313@users.noreply.github.com>
Co-authored-by: Youssef1313 <youssefvictor00@gmail.com>

Author: Copilot

src/Validation/gen/Emitters/ValidationsGenerator.Emitter.cs

@@ -15,18 +15,19 @@ public sealed partial class ValidationsGenerator : IIncrementalGenerator
     public static string GeneratedCodeConstructor => $@"global::System.CodeDom.Compiler.GeneratedCodeAttribute(""{typeof(ValidationsGenerator).Assembly.FullName}"", ""{typeof(ValidationsGenerator).Assembly.GetName().Version}"")";
     public static string GeneratedCodeAttribute => $"[{GeneratedCodeConstructor}]";
 
-    internal static void Emit(SourceProductionContext context, (InterceptableLocation? AddValidation, ImmutableArray<ValidatableType> ValidatableTypes) emitInputs)
+    internal static void Emit(SourceProductionContext context, (ImmutableArray<InterceptableLocation?> AddValidationLocations, ImmutableArray<ValidatableType> ValidatableTypes) emitInputs)
     {
-        if (emitInputs.AddValidation is null)
+        var locations = emitInputs.AddValidationLocations.OfType<InterceptableLocation>().ToImmutableArray();
+        if (locations.IsEmpty)
         {
             // Avoid generating code if no AddValidation call was found.
             return;
         }
-        var source = Emit(emitInputs.AddValidation, emitInputs.ValidatableTypes);
+        var source = Emit(locations, emitInputs.ValidatableTypes);
         context.AddSource("ValidatableInfoResolver.g.cs", SourceText.From(source, Encoding.UTF8));
     }
 
-    private static string Emit(InterceptableLocation addValidation, ImmutableArray<ValidatableType> validatableTypes) => $$"""
+    private static string Emit(ImmutableArray<InterceptableLocation> addValidationLocations, ImmutableArray<ValidatableType> validatableTypes) => $$"""
 #nullable enable annotations
 //------------------------------------------------------------------------------
 // <auto-generated>
@@ -115,7 +116,7 @@ public bool TryGetValidatableParameterInfo(global::System.Reflection.ParameterIn
     {{GeneratedCodeAttribute}}
     file static class GeneratedServiceCollectionExtensions
     {
-        {{addValidation.GetInterceptsLocationAttributeSyntax()}}
+        {{EmitAddValidationInterceptorAttributes(addValidationLocations)}}
         public static global::Microsoft.Extensions.DependencyInjection.IServiceCollection AddValidation(this global::Microsoft.Extensions.DependencyInjection.IServiceCollection services, global::System.Action<global::Microsoft.Extensions.Validation.ValidationOptions>? configureOptions = null)
         {
             // Use non-extension method to avoid infinite recursion.
@@ -325,6 +326,26 @@ private sealed record CacheKey(
 }
 """;
 
+    private static string EmitAddValidationInterceptorAttributes(ImmutableArray<InterceptableLocation> addValidations)
+    {
+        // We filtered early for empty locations, so we are sure we have at least one.
+        var firstAttribute = addValidations[0].GetInterceptsLocationAttributeSyntax();
+        if (addValidations.Length == 1)
+        {
+            // Common case
+            return firstAttribute;
+        }
+
+        // This is the less common case.
+        var sb = new StringBuilder(firstAttribute);
+        for (var i = 1; i < addValidations.Length; i++)
+        {
+            sb.AppendLine().Append("        ").Append(addValidations[i].GetInterceptsLocationAttributeSyntax());
+        }
+
+        return sb.ToString();
+    }
+
     private static string EmitTypeChecks(ImmutableArray<ValidatableType> validatableTypes)
     {
         var sw = new StringWriter();

src/Validation/gen/ValidationsGenerator.cs

@@ -50,7 +50,11 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
             .Distinct(ValidatableTypeComparer.Instance)
             .Collect();
 
-        var emitInputs = addValidation
+        // Collect all AddValidation call sites to avoid emitting duplicate hint names
+        // when AddValidation() is called multiple times in the same project.
+        var addValidationLocations = addValidation.Collect();
+
+        var emitInputs = addValidationLocations
             .Combine(validatableTypes);
 
         // Emit the IValidatableInfo resolver injection and

src/Validation/test/Microsoft.Extensions.Validation.GeneratorTests/ValidationsGenerator.NoOp.cs

@@ -178,4 +178,57 @@ await VerifyEndpoint(compilation, "/complex-type", async (endpoint, serviceProvi
             });
         });
     }
+
+    [Fact]
+    public async Task CanGenerateWhenAddValidationCalledMultipleTimes()
+    {
+        var source = """
+using System;
+using System.ComponentModel.DataAnnotations;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Validation;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.DependencyInjection;
+
+var builder = WebApplication.CreateBuilder();
+
+builder.Services.AddValidation();
+builder.Services.AddValidation(); // second call should not cause CS8785
+
+var app = builder.Build();
+
+app.MapPost("/complex-type", (ComplexType complexType) => Results.Ok("Passed"));
+
+app.Run();
+
+public class ComplexType
+{
+    [Range(10, 100)]
+    public int IntegerWithRange { get; set; } = 10;
+}
+""";
+        await Verify(source, out var compilation);
+        // Verify that types are still validated even with multiple AddValidation calls
+        await VerifyEndpoint(compilation, "/complex-type", async (endpoint, serviceProvider) =>
+        {
+            var payload = """
+                {
+                    "IntegerWithRange": 5
+                }
+                """;
+            var context = CreateHttpContextWithPayload(payload, serviceProvider);
+
+            await endpoint.RequestDelegate(context);
+
+            var problemDetails = await AssertBadRequest(context);
+            Assert.Collection(problemDetails.Errors, kvp =>
+            {
+                Assert.Equal("IntegerWithRange", kvp.Key);
+                Assert.Equal("The field IntegerWithRange must be between 10 and 100.", kvp.Value.Single());
+            });
+        });
+    }
 }

src/Validation/test/Microsoft.Extensions.Validation.GeneratorTests/ValidationsGeneratorTestBase.cs

@@ -57,6 +57,7 @@ internal static Task Verify(string source, out Compilation compilation)
                     MetadataReference.CreateFromFile(typeof(IFormFileCollection).Assembly.Location),
                     MetadataReference.CreateFromFile(typeof(PipeReader).Assembly.Location),
                     MetadataReference.CreateFromFile(typeof(System.ComponentModel.DataAnnotations.ValidationAttribute).Assembly.Location),
+                    MetadataReference.CreateFromFile(typeof(System.ComponentModel.DisplayNameAttribute).Assembly.Location),
                     MetadataReference.CreateFromFile(typeof(RouteData).Assembly.Location),
                     MetadataReference.CreateFromFile(typeof(IFeatureCollection).Assembly.Location),
                     MetadataReference.CreateFromFile(typeof(ValidateOptionsResult).Assembly.Location),