Use (project).blazor.config to allow calling UseBlazor with just an assembly name. Allows ReferenceOutputAssembly=false.

samples/HostedInAspNet.Server/HostedInAspNet.Server.csproj

@@ -10,7 +10,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\src\Microsoft.Blazor.Server\Microsoft.Blazor.Server.csproj" />
-    <ProjectReference Include="..\HostedInAspNet.Client\HostedInAspNet.Client.csproj" />
+    <ProjectReference Include="..\HostedInAspNet.Client\HostedInAspNet.Client.csproj" ReferenceOutputAssembly="false" />
   </ItemGroup>
 
 </Project>

samples/HostedInAspNet.Server/Startup.cs

@@ -24,9 +24,7 @@ namespace HostedInAspNet.Server
                 app.UseDeveloperExceptionPage();
             }
 
-            app.UseBlazor(
+            app.UseBlazor("HostedInAspNet.Client");
-                assemblyPath: typeof(Client.Program).Assembly.Location,
-                staticFilesRoot: "../HostedInAspNet.Client/wwwroot");
         }
     }
 }

samples/MonoSanity/MonoSanity.csproj

@@ -10,7 +10,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\src\Microsoft.Blazor.Server\Microsoft.Blazor.Server.csproj" />
-    <ProjectReference Include="..\MonoSanityClient\MonoSanityClient.csproj" />
+    <ProjectReference Include="..\MonoSanityClient\MonoSanityClient.csproj" ReferenceOutputAssembly="false" />
   </ItemGroup>
 
 </Project>

samples/MonoSanity/Startup.cs

@@ -12,9 +12,7 @@ namespace MonoSanity
         {
             app.UseDeveloperExceptionPage();
             app.UseFileServer(new FileServerOptions { EnableDefaultFiles = true });
-            app.UseBlazor(
+            app.UseBlazor("MonoSanityClient");
-                assemblyPath: typeof(MonoSanityClient.Examples).Assembly.Location,
-                staticFilesRoot: null);
         }
     }
 }

src/Microsoft.Blazor.DevHost/Server/Startup.cs

@@ -20,12 +20,12 @@ namespace Microsoft.Blazor.DevHost.Server
         public void Configure(IApplicationBuilder app)
         {
             app.UseDeveloperExceptionPage();
-            app.UseBlazor(
+
-                assemblyPath: FindClientAssembly(app).Location,
+            var clientAssemblyPath = FindClientAssemblyPath(app);
-                staticFilesRoot: "wwwroot");
+            app.UseBlazorInternal(clientAssemblyPath);
         }
 
-        private static Assembly FindClientAssembly(IApplicationBuilder app)
+        private static string FindClientAssemblyPath(IApplicationBuilder app)
         {
             var env = app.ApplicationServices.GetRequiredService<IHostingEnvironment>();
             var contentRoot = env.ContentRootPath;
@@ -37,7 +37,7 @@ namespace Microsoft.Blazor.DevHost.Server
                 throw new FileNotFoundException($"Could not locate application assembly at expected location {assemblyPath}");
             }
 
-            return Assembly.LoadFile(assemblyPath);
+            return assemblyPath;
         }
 
         private static string FindClientBinDir(string clientAppSourceRoot)

src/Microsoft.Blazor.Server/BlazorAppBuilderExtensions.cs

@@ -1,11 +1,10 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.StaticFiles;
+using Microsoft.Blazor.Server;
 using Microsoft.Blazor.Server.FrameworkFiles;
 using Microsoft.Blazor.Server.WebRootFiles;
-using Microsoft.Extensions.DependencyInjection;
 using System.Collections.Generic;
 using System.IO;
 using System.Net.Mime;
@@ -16,18 +15,28 @@ namespace Microsoft.AspNetCore.Builder
     {
         public static void UseBlazor(
             this IApplicationBuilder applicationBuilder,
-            string assemblyPath,
+            string clientAssemblyName)
-            string staticFilesRoot)
         {
-            var frameworkFileProvider = FrameworkFileProvider.Instantiate(assemblyPath);
+            var binDir = Path.GetDirectoryName(typeof(BlazorConfig).Assembly.Location);
+            var clientAssemblyPath = Path.Combine(binDir, $"{clientAssemblyName}.dll");
+            applicationBuilder.UseBlazorInternal(clientAssemblyPath);
+        }
 
-            if (staticFilesRoot != null)
+        // TODO: Change this combination of APIs to make it possible to supply either
+        // an assembly name (resolved to current bin dir) or full assembly path
+        internal static void UseBlazorInternal(
+            this IApplicationBuilder applicationBuilder,
+            string clientAssemblyPath)
+        {
+            var config = BlazorConfig.Read(clientAssemblyPath);
+            var frameworkFileProvider = FrameworkFileProvider.Instantiate(
+                config.SourceOutputAssemblyPath);
+
+            if (config.WebRootPath != null)
             {
-                var env = applicationBuilder.ApplicationServices.GetRequiredService<IHostingEnvironment>();
-                var clientWebRoot = Path.GetFullPath(Path.Combine(env.ContentRootPath, staticFilesRoot));
                 var webRootFileProvider = WebRootFileProvider.Instantiate(
-                    clientWebRoot,
+                    config.WebRootPath,
-                    Path.GetFileNameWithoutExtension(assemblyPath),
+                    Path.GetFileNameWithoutExtension(config.SourceOutputAssemblyPath),
                     frameworkFileProvider.GetDirectoryContents("/_bin"));
 
                 applicationBuilder.UseDefaultFiles(new DefaultFilesOptions

src/Microsoft.Blazor.Server/BlazorConfig.cs

@@ -0,0 +1,34 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.IO;
+using System.Linq;
+
+namespace Microsoft.Blazor.Server
+{
+    internal class BlazorConfig
+    {
+        public string SourceMSBuildPath { get; }
+        public string SourceOutputAssemblyPath { get; }
+        public string WebRootPath { get; }
+
+        public static BlazorConfig Read(string assemblyPath)
+            => new BlazorConfig(assemblyPath);
+
+        private BlazorConfig(string assemblyPath)
+        {
+            var configFilePath = Path.ChangeExtension(assemblyPath, ".blazor.config");
+            var configLines = File.ReadLines(configFilePath).ToList();
+            SourceMSBuildPath = configLines[0];
+
+            var sourceMsBuildDir = Path.GetDirectoryName(SourceMSBuildPath);
+            SourceOutputAssemblyPath = Path.Combine(sourceMsBuildDir, configLines[1]);
+
+            var webRootPath = Path.Combine(sourceMsBuildDir, "wwwroot");
+            if (Directory.Exists(webRootPath))
+            {
+                WebRootPath = webRootPath;
+            }
+        }
+    }
+}

src/Microsoft.Blazor.Server/Properties/AssemblyInfo.cs

@@ -1,3 +1,4 @@
 using System.Runtime.CompilerServices;
 
+[assembly: InternalsVisibleTo("Microsoft.Blazor.DevHost")]
 [assembly: InternalsVisibleTo("Microsoft.Blazor.Server.Test")]