Fix dotnet-blazor serve

This wasn't properly forwarding the base path to the configuration.
Basically nothing was setting RemainingArguments. We have a test project
that sets the base path, but it was never used when debugging locally.

I also cleaned this up a bit and changed it to use dotnet exec. This
allow you to debug the CLI and related server pipeline, but has the
tradeoff of not rebuilding.

src/Components/blazor/benchmarks/Microsoft.AspNetCore.Blazor.E2EPerformance/Microsoft.AspNetCore.Blazor.E2EPerformance.csproj

@@ -2,10 +2,6 @@
 
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
-
-    <!-- Local alternative to <RunArguments>blazor serve</RunArguments> -->
-    <RunCommand>dotnet</RunCommand>
-    <RunArguments>run --project ../../../blazor/src/Microsoft.AspNetCore.Blazor.Cli serve</RunArguments>
   </PropertyGroup>
 
   <ItemGroup>

src/Components/blazor/samples/StandaloneApp/StandaloneApp.csproj

@@ -2,10 +2,6 @@
 
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
-
-    <!-- Local alternative to <RunArguments>blazor serve</RunArguments> -->
-    <RunCommand>dotnet</RunCommand>
-    <RunArguments>run --project ../../src/Microsoft.AspNetCore.Blazor.Cli serve</RunArguments>
   </PropertyGroup>
 
   <ItemGroup>

src/Components/blazor/src/Microsoft.AspNetCore.Blazor.Cli/Commands/ServeCommand.cs

@@ -3,19 +3,30 @@
 
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.CommandLineUtils;
-using System;
-using System.Diagnostics;
-using System.Text.RegularExpressions;
 
 namespace Microsoft.AspNetCore.Blazor.Cli.Commands
 {
-    class ServeCommand
+    internal class ServeCommand : CommandLineApplication
     {
-        public static void Command(CommandLineApplication command)
-        {
-            var remainingArgs = command.RemainingArguments.ToArray();
+        public ServeCommand(CommandLineApplication parent)
 
-            Server.Program.BuildWebHost(remainingArgs).Run();
+            // We pass arbitrary arguments through to the ASP.NET Core configuration
+            : base(throwOnUnexpectedArg: false) 
+        {
+            Parent = parent;
+            
+            Name = "serve";
+            Description = "Serve requests to a Blazor application";
+
+            HelpOption("-?|-h|--help");
+
+            OnExecute(Execute);
+        }
+
+        private int Execute()
+        {
+            Server.Program.BuildWebHost(RemainingArguments.ToArray()).Run();
+            return 0;
         }
     }
 }

src/Components/blazor/src/Microsoft.AspNetCore.Blazor.Cli/Program.cs

@@ -1,11 +1,8 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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 System;
-using System.Linq;
-using Microsoft.Extensions.CommandLineUtils;
 using Microsoft.AspNetCore.Blazor.Cli.Commands;
+using Microsoft.Extensions.CommandLineUtils;
 
 namespace Microsoft.AspNetCore.Blazor.Cli
 {
@@ -13,22 +10,30 @@ namespace Microsoft.AspNetCore.Blazor.Cli
     {
         static int Main(string[] args)
         {
-            var app = new CommandLineApplication
+            var app = new CommandLineApplication(throwOnUnexpectedArg: false)
             {
                 Name = "blazor-cli"
             };
             app.HelpOption("-?|-h|--help");
 
-            app.Command("serve", ServeCommand.Command);
+            app.Commands.Add(new ServeCommand(app));
 
-            if (args.Length > 0)
-            {
-                return app.Execute(args);
-            }
-            else
+            // A command is always required
+            app.OnExecute(() =>
             {
                 app.ShowHelp();
                 return 0;
+            });
+
+            try
+            {
+                return app.Execute(args);
+            }
+            catch (CommandParsingException cex)
+            {
+                app.Error.WriteLine(cex.Message);
+                app.ShowHelp();
+                return 1;
             }
         }
     }

src/Components/src/Microsoft.AspNetCore.Components.Build/ReferenceFromSource.props

@@ -1,4 +1,4 @@
-<Project>
+<Project>
 
   <!--
   Importing this file is equivalent to having:
@@ -17,6 +17,20 @@
   <Import Project="$(MSBuildThisFileDirectory)targets/All.props" />
   <Import Project="$(MSBuildThisFileDirectory)targets/All.targets" />
 
+  <!-- 
+    Debugging support using dotnet-blazor serve.
+
+    A few things to note here:
+      - We have to use dotnet exec to avoid launching another process and confusing the debugger.
+      - Since we're doing dotnet exec, it won't automatically rebuild the CLI project.
+      - $(AdditionalRunArguments) needs to be defined before importing this file.
+   -->
+  <PropertyGroup>
+    <RunCommand>dotnet</RunCommand>
+    <_BlazorCliLocation>$(MSBuildThisFileDirectory)../../blazor/src/Microsoft.AspNetCore.Blazor.Cli/bin/$(Configuration)/netcoreapp3.0/dotnet-blazor.dll </_BlazorCliLocation>
+    <RunArguments>exec $(_BlazorCliLocation) serve $(AdditionalRunArguments)</RunArguments>
+  </PropertyGroup>
+
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.Blazor.Mono" Version="$(MicrosoftAspNetCoreBlazorMonoPackageVersion)" />
     <PackageReference Include="Microsoft.AspNetCore.Razor.Design" Version="$(MicrosoftAspNetCoreRazorDesignPackageVersion)" />

src/Components/test/testapps/BasicTestApp/BasicTestApp.csproj

@@ -3,9 +3,8 @@
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
 
-    <!-- Local alternative to <RunArguments>blazor serve</RunArguments> -->
-    <RunCommand>dotnet</RunCommand>
-    <RunArguments>run --project ../../../blazor/src/Microsoft.AspNetCore.Blazor.Cli serve --pathbase /subdir</RunArguments>
+    <!-- Must be defined before ReferenceFromSource.props is imported -->
+    <AdditionalRunArguments>--pathbase /subdir</AdditionalRunArguments>
   </PropertyGroup>
 
   <!-- Local alternative to <PackageReference Include="Microsoft.AspNetCore.Components.Build" /> -->