[release/11.0-preview3] Fix publish-time Framework materialization for multi-client WASM and add test

src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets

@@ -753,7 +753,13 @@ Copyright (c) .NET Foundation. All rights reserved.
 
       <!-- remove the original assemblies -->
       <ResolvedFileToPublish Remove="@(WasmAssembliesToBundle)" />
-      <_WasmResolvedFilesToPublish Include="@(ResolvedFileToPublish)" />
+      <!-- Exclude items marked CopyToPublishDirectory=Never. These are build-only assets
+           (e.g., HotReload dll) that should not participate in publish. Without this filter,
+           ComputeWasmPublishAssets matches them by filename and replaces Framework-materialized
+           per-project assets with the raw SDK-path original, causing duplicate Identity crashes
+           in multi-client hosted publish scenarios. -->
+      <_WasmResolvedFilesToPublish Include="@(ResolvedFileToPublish)"
+        Condition="'%(ResolvedFileToPublish.CopyToPublishDirectory)' != 'Never'" />
     </ItemGroup>
 
     <ComputeWasmPublishAssets

src/mono/wasm/Wasm.Build.Tests/Blazor/MiscTests.cs

@@ -103,79 +103,61 @@ public void BugRegression_60479_WithRazorClassLib()
     }
 
     [Theory]
-    [InlineData(Configuration.Debug)]
-    [InlineData(Configuration.Release)]
-    public void MultiClientHostedBuild(Configuration config)
+    [InlineData(Configuration.Debug, false)]
+    [InlineData(Configuration.Release, false)]
+    [InlineData(Configuration.Debug, true)]
+    [InlineData(Configuration.Release, true)]
+    public void MultiClientHostedBuildAndPublish(Configuration config, bool publish)
     {
-        // Test that two Blazor WASM client projects can be hosted by a single server project
-        // without duplicate static web asset Identity collisions. This validates the Framework
-        // SourceType materialization path that gives each client unique per-project Identity
-        // for shared runtime pack files.
-        ProjectInfo info = CopyTestAsset(config, aot: false, TestAsset.BlazorBasicTestApp, "multi_hosted");
-
-        // _projectDir is now .../App. Go up to the root and create a second client + server.
-        string rootDir = Path.GetDirectoryName(_projectDir)!;
-        string client1Dir = _projectDir;
-        string client2Dir = Path.Combine(rootDir, "App2");
-        string serverDir = Path.Combine(rootDir, "Server");
-
-        // Duplicate App as App2 with a different StaticWebAssetBasePath
-        Utils.DirectoryCopy(client1Dir, client2Dir);
-        string client2Csproj = Path.Combine(client2Dir, "BlazorBasicTestApp.csproj");
-        File.Move(client2Csproj, Path.Combine(client2Dir, "BlazorBasicTestApp2.csproj"));
-        client2Csproj = Path.Combine(client2Dir, "BlazorBasicTestApp2.csproj");
-
-        // Set different base paths so the two clients don't collide on routes
-        AddItemsPropertiesToProject(Path.Combine(client1Dir, "BlazorBasicTestApp.csproj"),
-            extraProperties: "<StaticWebAssetBasePath>client1</StaticWebAssetBasePath>");
-        AddItemsPropertiesToProject(client2Csproj,
-            extraProperties: "<StaticWebAssetBasePath>client2</StaticWebAssetBasePath><RootNamespace>BlazorBasicTestApp</RootNamespace>");
-
-        // Create a minimal server project that references both clients
-        Directory.CreateDirectory(serverDir);
-        string serverCsproj = Path.Combine(serverDir, "Server.csproj");
-        File.WriteAllText(serverCsproj, $"""
-            <Project Sdk="Microsoft.NET.Sdk.Web">
-              <PropertyGroup>
-                <TargetFramework>{DefaultTargetFrameworkForBlazor}</TargetFramework>
-                <Nullable>enable</Nullable>
-                <ImplicitUsings>enable</ImplicitUsings>
-              </PropertyGroup>
-              <ItemGroup>
-                <ProjectReference Include="..\App\BlazorBasicTestApp.csproj" />
-                <ProjectReference Include="..\App2\BlazorBasicTestApp2.csproj" />
-              </ItemGroup>
-            </Project>
-            """);
-        File.WriteAllText(Path.Combine(serverDir, "Program.cs"), """
-            var builder = WebApplication.CreateBuilder(args);
-            var app = builder.Build();
-            app.UseStaticFiles();
-            app.Run();
-            """);
-
-        // Build the server project — this will transitively build both clients.
-        // Without Framework materialization, this would fail with duplicate Identity
-        // for shared runtime pack files (dotnet.native.js, ICU data, etc.)
-        string logPath = Path.Combine(s_buildEnv.LogRootPath, info.ProjectName, $"{info.ProjectName}-multi-hosted.binlog");
+        // Test that two Blazor WASM client projects can be built/published by a single server
+        // project without duplicate static web asset Identity collisions. This validates the
+        // Framework SourceType materialization path that gives each client unique per-project
+        // Identity for shared runtime pack files.
+        string id = publish ? "multi_pub" : "multi_hosted";
+        CopyTestAsset(config, aot: false, TestAsset.BlazorMultiClientHosted, id);
+
+        string serverDir = _projectDir;
+        string rootDir = Path.GetDirectoryName(serverDir)!;
+        string client1Dir = Path.Combine(rootDir, "Client1");
+        string client2Dir = Path.Combine(rootDir, "Client2");
+
+        string command = publish ? "publish" : "build";
+        string logPath = Path.Combine(_logPath, $"{id}-{config}-{command}.binlog");
         using ToolCommand cmd = new DotNetCommand(s_buildEnv, _testOutput)
                                     .WithWorkingDirectory(serverDir);
-        CommandResult result = cmd
+        _ = cmd
             .WithEnvironmentVariable("NUGET_PACKAGES", _nugetPackagesDir)
-            .ExecuteWithCapturedOutput("build", $"-p:Configuration={config}", $"-bl:{logPath}")
+            .ExecuteWithCapturedOutput(command, $"-p:Configuration={config}", $"-bl:{logPath}")
             .EnsureSuccessful();
 
-        // Verify both clients produced framework files in their own bin directories
-        string client1Framework = Path.Combine(client1Dir, "bin", config.ToString(), DefaultTargetFrameworkForBlazor, "wwwroot", "_framework");
-        string client2Framework = Path.Combine(client2Dir, "bin", config.ToString(), DefaultTargetFrameworkForBlazor, "wwwroot", "_framework");
-
-        Assert.True(Directory.Exists(client1Framework), $"Client1 framework dir missing: {client1Framework}");
-        Assert.True(Directory.Exists(client2Framework), $"Client2 framework dir missing: {client2Framework}");
-
-        // Both should have dotnet.js (verifies framework files were materialized per-client)
-        var client1Files = Directory.GetFiles(client1Framework);
-        var client2Files = Directory.GetFiles(client2Framework);
-        Assert.Contains(client1Files, f => Path.GetFileName(f).StartsWith("dotnet.") && f.EndsWith(".js"));
-        Assert.Contains(client2Files, f => Path.GetFileName(f).StartsWith("dotnet.") && f.EndsWith(".js"));
+        if (publish)
+        {
+            string publishDir = Path.Combine(serverDir, "bin", config.ToString(), DefaultTargetFrameworkForBlazor, "publish");
+            string client1Framework = Path.Combine(publishDir, "wwwroot", "client1", "_framework");
+            string client2Framework = Path.Combine(publishDir, "wwwroot", "client2", "_framework");
+
+            Assert.True(Directory.Exists(client1Framework), $"Client1 publish framework dir missing: {client1Framework}");
+            Assert.True(Directory.Exists(client2Framework), $"Client2 publish framework dir missing: {client2Framework}");
+
+            var client1Files = Directory.GetFiles(client1Framework);
+            var client2Files = Directory.GetFiles(client2Framework);
+            Assert.Contains(client1Files, f => Path.GetFileName(f).StartsWith("dotnet.") && f.EndsWith(".js"));
+            Assert.Contains(client2Files, f => Path.GetFileName(f).StartsWith("dotnet.") && f.EndsWith(".js"));
+            Assert.Contains(client1Files, f => Path.GetFileName(f).Contains("dotnet.native") && f.EndsWith(".wasm"));
+            Assert.Contains(client2Files, f => Path.GetFileName(f).Contains("dotnet.native") && f.EndsWith(".wasm"));
+        }
+        else
+        {
+            string client1Framework = Path.Combine(client1Dir, "bin", config.ToString(), DefaultTargetFrameworkForBlazor, "wwwroot", "_framework");
+            string client2Framework = Path.Combine(client2Dir, "bin", config.ToString(), DefaultTargetFrameworkForBlazor, "wwwroot", "_framework");
+
+            Assert.True(Directory.Exists(client1Framework), $"Client1 framework dir missing: {client1Framework}");
+            Assert.True(Directory.Exists(client2Framework), $"Client2 framework dir missing: {client2Framework}");
+
+            var client1Files = Directory.GetFiles(client1Framework);
+            var client2Files = Directory.GetFiles(client2Framework);
+            Assert.Contains(client1Files, f => Path.GetFileName(f).StartsWith("dotnet.") && f.EndsWith(".js"));
+            Assert.Contains(client2Files, f => Path.GetFileName(f).StartsWith("dotnet.") && f.EndsWith(".js"));
+        }
     }
 }

src/mono/wasm/Wasm.Build.Tests/BrowserStructures/TestAsset.cs

@@ -6,4 +6,5 @@ public class TestAsset
     public static readonly TestAsset BlazorBasicTestApp = new() { Name = "BlazorBasicTestApp", RunnableProjectSubPath = "App" };
     public static readonly TestAsset LibraryModeTestApp = new() { Name = "LibraryMode" };
     public static readonly TestAsset BlazorWebWasm = new() { Name = "BlazorWebWasm", RunnableProjectSubPath = "BlazorWebWasm" };
+    public static readonly TestAsset BlazorMultiClientHosted = new() { Name = "BlazorMultiClientHosted", RunnableProjectSubPath = "Server" };
 }

src/mono/wasm/testassets/BlazorMultiClientHosted/Client1/App.razor

@@ -0,0 +1 @@
+<h1>Client 1</h1>

src/mono/wasm/testassets/BlazorMultiClientHosted/Client1/Client1.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk.BlazorWebAssembly">
+  <PropertyGroup>
+    <TargetFramework>net11.0</TargetFramework>
+    <StaticWebAssetBasePath>client1</StaticWebAssetBasePath>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly" Version="10.0.0-alpha.2.25073.4" />
+  </ItemGroup>
+</Project>

src/mono/wasm/testassets/BlazorMultiClientHosted/Client1/Program.cs

@@ -0,0 +1,3 @@
+using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
+var builder = WebAssemblyHostBuilder.CreateDefault(args);
+await builder.Build().RunAsync();

src/mono/wasm/testassets/BlazorMultiClientHosted/Client2/App.razor

@@ -0,0 +1 @@
+<h1>Client 2</h1>

src/mono/wasm/testassets/BlazorMultiClientHosted/Client2/Client2.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk.BlazorWebAssembly">
+  <PropertyGroup>
+    <TargetFramework>net11.0</TargetFramework>
+    <StaticWebAssetBasePath>client2</StaticWebAssetBasePath>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly" Version="10.0.0-alpha.2.25073.4" />
+  </ItemGroup>
+</Project>

src/mono/wasm/testassets/BlazorMultiClientHosted/Client2/Program.cs

@@ -0,0 +1,3 @@
+using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
+var builder = WebAssemblyHostBuilder.CreateDefault(args);
+await builder.Build().RunAsync();

src/mono/wasm/testassets/BlazorMultiClientHosted/Server/BlazorMultiClientHosted.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+  <PropertyGroup>
+    <TargetFramework>net11.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\Client1\Client1.csproj" />
+    <ProjectReference Include="..\Client2\Client2.csproj" />
+  </ItemGroup>
+</Project>

src/mono/wasm/testassets/BlazorMultiClientHosted/Server/Program.cs

@@ -0,0 +1,4 @@
+var builder = WebApplication.CreateBuilder(args);
+var app = builder.Build();
+app.UseStaticFiles();
+app.Run();

src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/ComputeWasmPublishAssets.cs

@@ -458,7 +458,21 @@ private void ComputeUpdatedAssemblies(
                 filesToRemove.Add(existing);
                 if (!string.Equals(asset.ItemSpec, existing.GetMetadata("FullPath"), StringComparison.Ordinal))
                 {
-                    linkedAssets.Add(asset.ItemSpec, existing);
+                    // Don't replace Framework-materialized assets. These have unique per-project
+                    // paths (from UpdatePackageStaticWebAssets) that must be preserved in multi-client
+                    // hosted scenarios. Replacing them with the ResolvedFileToPublish item (which
+                    // points to the shared SDK/NuGet path) would cause duplicate Identity crashes.
+                    var assetSourceType = asset.GetMetadata("SourceType");
+                    if (!string.Equals(assetSourceType, "Discovered", StringComparison.OrdinalIgnoreCase) ||
+                        asset.ItemSpec.IndexOf(Path.DirectorySeparatorChar + "fx" + Path.DirectorySeparatorChar, StringComparison.OrdinalIgnoreCase) < 0)
+                    {
+                        linkedAssets.Add(asset.ItemSpec, existing);
+                    }
+                    else
+                    {
+                        Log.LogMessage(MessageImportance.Low, "Skipping replacement of Framework-materialized asset '{0}' with '{1}'",
+                            asset.ItemSpec, existing.GetMetadata("FullPath"));
+                    }
                 }
             }
             else
@@ -722,6 +736,16 @@ private void GroupResolvedFilesToPublish(
                 continue;
             }
 
+            // Skip items explicitly marked as not for publish. These should not be used
+            // to replace build-time assets (e.g., Framework-materialized assets that have
+            // unique per-project paths would otherwise be replaced by the raw SDK-path
+            // original, causing duplicate Identity crashes in multi-client hosted scenarios).
+            if (string.Equals(candidate.GetMetadata("CopyToPublishDirectory"), "Never", StringComparison.OrdinalIgnoreCase))
+            {
+                Log.LogMessage(MessageImportance.Low, "Skipping asset '{0}' because CopyToPublishDirectory is 'Never'", candidate.ItemSpec);
+                continue;
+            }
+
             var fileName = candidate.GetMetadata("FileName");
             var extension = candidate.GetMetadata("Extension");
             if (string.Equals(candidate.GetMetadata("AssetType"), "native", StringComparison.Ordinal) && (fileName == "dotnet" || fileName == "dotnet.native") && extension == ".wasm")