Merge duplicate tag helper descriptors

src/Compiler/Microsoft.AspNetCore.Razor.Language/src/DefaultRazorTagHelperContextDiscoveryPhase.cs

@@ -65,7 +65,21 @@ protected override void ExecuteCore(RazorCodeDocument codeDocument)
         // This will always be null for a component document.
         var tagHelperPrefix = visitor.TagHelperPrefix;
 
-        descriptors = visitor.Matches.ToArray();
+        // Merge descriptors with the same full name to deduplicate partial class definitions.
+        var finalDescriptors = new Dictionary<TagHelperDescriptor, TagHelperDescriptor>(TagHelperDescriptorSimpleComparer.Default);
+        foreach (var descriptor in visitor.Matches)
+        {
+            if (finalDescriptors.TryGetValue(descriptor, out var existing))
+            {
+                finalDescriptors[descriptor] = TagHelperDescriptor.Merge(existing, descriptor);
+            }
+            else
+            {
+                finalDescriptors.Add(descriptor, descriptor);
+            }
+        }
+
+        descriptors = finalDescriptors.Values.ToArray();
 
         var context = TagHelperDocumentContext.Create(tagHelperPrefix, descriptors);
         codeDocument.SetTagHelperContext(context);

src/Compiler/Microsoft.AspNetCore.Razor.Language/src/TagHelperDescriptor.cs

@@ -216,6 +216,33 @@ public virtual IEnumerable<RazorDiagnostic> GetAllDiagnostics()
         return _allDiagnostics;
     }
 
+    internal static TagHelperDescriptor Merge(TagHelperDescriptor x, TagHelperDescriptor y)
+    {
+        Debug.Assert(x.Kind == y.Kind &&
+            x.Name == y.Name &&
+            x.AssemblyName == y.AssemblyName &&
+            x.DisplayName == y.DisplayName);
+
+        var merged = new DefaultTagHelperDescriptor(
+            kind: x.Kind,
+            name: x.Name,
+            assemblyName: x.AssemblyName,
+            displayName: x.DisplayName,
+            documentationObject: x.DocumentationObject.Object is null ? y.DocumentationObject : x.DocumentationObject,
+            tagOutputHint: x.TagOutputHint ?? y.TagOutputHint,
+            caseSensitive: x.CaseSensitive || y.CaseSensitive,
+            tagMatchingRules: x.TagMatchingRules.Union(y.TagMatchingRules).ToArray(),
+            attributeDescriptors: x.BoundAttributes.Union(y.BoundAttributes).ToArray(),
+            allowedChildTags: x.AllowedChildTags.Union(y.AllowedChildTags).ToArray(),
+            metadata: MetadataCollection.Create(x.Metadata.Union(y.Metadata).ToArray()),
+            diagnostics: x.Diagnostics.Union(y.Diagnostics).ToArray());
+
+        Debug.Assert(TagHelperDescriptorSimpleComparer.Default.Equals(x, merged) &&
+            TagHelperDescriptorSimpleComparer.Default.Equals(y, merged));
+
+        return merged;
+    }
+
     public override string ToString()
     {
         return DisplayName ?? base.ToString();

src/Compiler/Microsoft.AspNetCore.Razor.Language/src/TagHelperDescriptorSimpleComparer.cs

@@ -0,0 +1,46 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using Microsoft.AspNetCore.Razor.Language.Components;
+using Microsoft.Extensions.Internal;
+
+namespace Microsoft.AspNetCore.Razor.Language;
+
+/// <summary>
+/// Considers two descriptors equal if they are definitions of the same class.
+/// </summary>
+internal sealed class TagHelperDescriptorSimpleComparer : IEqualityComparer<TagHelperDescriptor>
+{
+    public static readonly TagHelperDescriptorSimpleComparer Default = new();
+
+    private TagHelperDescriptorSimpleComparer() { }
+
+    public bool Equals(TagHelperDescriptor? x, TagHelperDescriptor? y)
+    {
+        if (ReferenceEquals(x, y))
+        {
+            return true;
+        }
+
+        if (x is null || y is null)
+        {
+            return false;
+        }
+
+        return x.Kind == y.Kind &&
+            x.AssemblyName == y.AssemblyName &&
+            x.Name == y.Name &&
+            x.IsComponentFullyQualifiedNameMatch() == y.IsComponentFullyQualifiedNameMatch();
+    }
+
+    public int GetHashCode(TagHelperDescriptor obj)
+    {
+        var hash = HashCodeCombiner.Start();
+        hash.Add(obj.Kind, StringComparer.Ordinal);
+        hash.Add(obj.AssemblyName, StringComparer.Ordinal);
+        hash.Add(obj.Name, StringComparer.Ordinal);
+        return hash.CombinedHash;
+    }
+}

src/Compiler/Microsoft.NET.Sdk.Razor.SourceGenerators/RazorSourceGenerator.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Immutable;
-using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using Microsoft.AspNetCore.Razor.Language;
@@ -115,7 +114,6 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
                     if (root is CompilationUnitSyntax { Members: [NamespaceDeclarationSyntax { Members: [ClassDeclarationSyntax classSyntax, ..] }, ..] })
                     {
                         var declaredClass = compilationWithDeclarations.GetSemanticModel(generatedDeclarationSyntaxTree).GetDeclaredSymbol(classSyntax, ct);
-                        Debug.Assert(declaredClass is null || declaredClass is { AllInterfaces: [{ Name: "IComponent" }, ..] });
                         targetSymbol = declaredClass ?? targetSymbol;
                     }
 

src/Compiler/test/Microsoft.NET.Sdk.Razor.SourceGenerators.Tests/RazorSourceGeneratorComponentTests.cs

@@ -0,0 +1,105 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Test.Common;
+using Xunit;
+
+namespace Microsoft.NET.Sdk.Razor.SourceGenerators;
+
+public sealed class RazorSourceGeneratorComponentTests : RazorSourceGeneratorTestsBase
+{
+    [Fact, WorkItem("https://github.com/dotnet/razor/issues/8718")]
+    public async Task PartialClass()
+    {
+        // Arrange
+        var project = CreateTestProject(new()
+        {
+            ["Views/Home/Index.cshtml"] = """
+                @(await Html.RenderComponentAsync<MyApp.Shared.Component1>(RenderMode.Static))
+                """,
+            ["Shared/Component1.razor"] = """
+                <Component2 Param="42" />
+                """,
+            ["Shared/Component2.razor"] = """
+                @inherits ComponentBase
+
+                Value: @(Param + 1)
+
+                @code {
+                    [Parameter]
+                    public int Param { get; set; }
+                }
+                """
+        }, new()
+        {
+            ["Component2.razor.cs"] = """
+                using Microsoft.AspNetCore.Components;
+
+                namespace MyApp.Shared;
+
+                public partial class Component2 : ComponentBase { }
+                """
+        });
+        var compilation = await project.GetCompilationAsync();
+        var driver = await GetDriverAsync(project, options =>
+        {
+            options.TestGlobalOptions["build_property.RazorLangVersion"] = "7.0";
+        });
+
+        // Act
+        var result = RunGenerator(compilation!, ref driver, out compilation);
+
+        // Assert
+        Assert.Empty(result.Diagnostics);
+        Assert.Equal(3, result.GeneratedSources.Length);
+        await VerifyRazorPageMatchesBaselineAsync(compilation, "Views_Home_Index");
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/razor/issues/8718")]
+    public async Task PartialClass_NoBaseInCSharp()
+    {
+        // Arrange
+        var project = CreateTestProject(new()
+        {
+            ["Views/Home/Index.cshtml"] = """
+                @(await Html.RenderComponentAsync<MyApp.Shared.Component1>(RenderMode.Static))
+                """,
+            ["Shared/Component1.razor"] = """
+                <Component2 Param="42" />
+                """,
+            ["Shared/Component2.razor"] = """
+                @inherits ComponentBase
+
+                Value: @(Param + 1)
+
+                @code {
+                    [Parameter]
+                    public int Param { get; set; }
+                }
+                """
+        }, new()
+        {
+            ["Component2.razor.cs"] = """
+                using Microsoft.AspNetCore.Components;
+
+                namespace MyApp.Shared;
+
+                public partial class Component2 { }
+                """
+        });
+        var compilation = await project.GetCompilationAsync();
+        var driver = await GetDriverAsync(project, options =>
+        {
+            options.TestGlobalOptions["build_property.RazorLangVersion"] = "7.0";
+        });
+
+        // Act
+        var result = RunGenerator(compilation!, ref driver, out compilation);
+
+        // Assert
+        Assert.Empty(result.Diagnostics);
+        Assert.Equal(3, result.GeneratedSources.Length);
+        await VerifyRazorPageMatchesBaselineAsync(compilation, "Views_Home_Index");
+    }
+}

src/Compiler/test/Microsoft.NET.Sdk.Razor.SourceGenerators.Tests/RazorSourceGeneratorTagHelperTests.cs

@@ -5,6 +5,7 @@
 
 using System.Linq;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Test.Common;
 using Microsoft.CodeAnalysis.CSharp;
 using Xunit;
 
@@ -1253,4 +1254,54 @@ public override void Process(TagHelperContext context, TagHelperOutput output)
         // Assert
         await VerifyRazorPageMatchesBaselineAsync(compilation, "Views_Home_Index");
     }
+
+    [Fact, WorkItem("https://github.com/dotnet/razor/issues/8718")]
+    public async Task ComponentAndTagHelper()
+    {
+        // Arrange
+        var project = CreateTestProject(new()
+        {
+            ["Views/Home/Index.cshtml"] = """
+                @addTagHelper *, TestProject
+
+                <email mail="example">custom tag helper</email>
+                """,
+            ["Shared/EmailTagHelper.razor"] = """
+                @inherits ComponentAndTagHelper
+                @code {
+                    public string? Mail { get; set; }
+                }
+                """,
+        }, new()
+        {
+            ["EmailTagHelper.cs"] = """
+                using Microsoft.AspNetCore.Razor.TagHelpers;
+                namespace MyApp.Shared;
+
+                public abstract class ComponentAndTagHelper : TagHelper
+                {
+                    protected abstract void BuildRenderTree(Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder __builder);
+                }
+
+                public partial class EmailTagHelper : ComponentAndTagHelper
+                {
+                    public override void Process(TagHelperContext context, TagHelperOutput output)
+                    {
+                        output.TagName = "a";
+                        output.Attributes.SetAttribute("href", $"mailto:{Mail}");
+                    }
+                }
+                """
+        });
+        var compilation = await project.GetCompilationAsync();
+        var driver = await GetDriverAsync(project);
+
+        // Act
+        var result = RunGenerator(compilation!, ref driver, out compilation);
+
+        // Assert
+        Assert.Empty(result.Diagnostics);
+        Assert.Equal(2, result.GeneratedSources.Length);
+        await VerifyRazorPageMatchesBaselineAsync(compilation, "Views_Home_Index");
+    }
 }

src/Compiler/test/Microsoft.NET.Sdk.Razor.SourceGenerators.Tests/RazorSourceGeneratorTestsBase.cs

@@ -17,6 +17,7 @@
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.ApplicationParts;
@@ -154,6 +155,14 @@ protected static async Task<string> RenderRazorPageAsync(Compilation compilation
         {
             RequestServices = app.Services
         };
+        var requestFeature = new HttpRequestFeature
+        {
+            Method = HttpMethods.Get,
+            Protocol = HttpProtocol.Http2,
+            Scheme = "http"
+        };
+        requestFeature.Headers.Host = "localhost";
+        httpContext.Features.Set<IHttpRequestFeature>(requestFeature);
         var actionContext = new ActionContext(
             httpContext,
             new AspNetCore.Routing.RouteData(),

src/Compiler/test/Microsoft.NET.Sdk.Razor.SourceGenerators.Tests/TestFiles/RazorSourceGeneratorComponentTests/PartialClass/Views_Home_Index.html

@@ -0,0 +1,2 @@
+
+Value: 43

src/Compiler/test/Microsoft.NET.Sdk.Razor.SourceGenerators.Tests/TestFiles/RazorSourceGeneratorComponentTests/PartialClass_NoBaseInCSharp/Views_Home_Index.html

@@ -0,0 +1,2 @@
+
+Value: 43

src/Compiler/test/Microsoft.NET.Sdk.Razor.SourceGenerators.Tests/TestFiles/RazorSourceGeneratorTagHelperTests/ComponentAndTagHelper/Views_Home_Index.html

@@ -0,0 +1,2 @@
+
+<a href="mailto:example">custom tag helper</a>