Add subsystem implementing response file handling

src/System.CommandLine.Subsystems.Tests/ResponseSubsystemTests.cs

@@ -0,0 +1,31 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using FluentAssertions;
+using System.CommandLine.Directives;
+using System.CommandLine.Parsing;
+using Xunit;
+
+namespace System.CommandLine.Subsystems.Tests;
+
+public class ResponseSubsystemTests
+{
+
+    [Fact]
+    // TODO: Not sure why these tests are passing
+    public void Simple_response_file_contributes_to_parsing()
+    {
+        var option = new CliOption<string>("--hello");
+        var rootCommand = new CliRootCommand { option };
+        var configuration = new CliConfiguration(rootCommand);
+        var subsystem = new ResponseSubsystem();
+        string[] args = ["@Response_1.rsp"];
+
+        Subsystem.Initialize(subsystem, configuration, args);
+
+        var parseResult = CliParser.Parse(rootCommand, args, configuration);
+        var value = parseResult.GetValue(option);
+
+        value.Should().Be("world");
+    }
+}

src/System.CommandLine.Subsystems.Tests/Response_1.rsp

@@ -0,0 +1 @@
+--hello world

src/System.CommandLine.Subsystems.Tests/System.CommandLine.Subsystems.Tests.csproj

@@ -16,6 +16,7 @@
   <ItemGroup>
     <Content Include="TestApps/**/*.csproj" CopyToOutputDirectory="PreserveNewest" />
     <Content Include="TestApps/**/*.cs" CopyToOutputDirectory="PreserveNewest" />
+    <Content Include="Response_1.rsp" CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>
 
   <ItemGroup>
@@ -31,6 +32,7 @@
     -->
     <Compile Include="AlternateSubsystems.cs" />
     <Compile Include="Constants.cs" />
+    <Compile Include="ResponseSubsystemTests.cs" />
     <Compile Include="DirectiveSubsystemTests.cs" />
     <Compile Include="DiagramSubsystemTests.cs" />
     <Compile Include="PipelineTests.cs" />

src/System.CommandLine.Subsystems/Directives/ResponseSubsystem.cs

@@ -0,0 +1,103 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.CommandLine.Parsing;
+using System.CommandLine.Subsystems;
+
+namespace System.CommandLine.Directives;
+
+public class ResponseSubsystem()
+    : CliSubsystem("Response", SubsystemKind.Response, null)
+{
+    protected internal override CliConfiguration Initialize(InitializationContext context)
+    {
+        context.Configuration.ResponseFileTokenReplacer = Replacer;
+        return context.Configuration;
+    }
+
+    public static (List<string>? tokens, List<string>? errors) Replacer(string responseSourceName)
+    {
+        try
+        {
+            // TODO: Include checks from previous system.
+            var contents = File.ReadAllText(responseSourceName);
+            return (CliParser.SplitCommandLine(contents).ToList(), null);
+        }
+        catch
+        {
+            // TODO: Switch to proper errors
+            return (null,
+                    errors:
+                    [
+                        $"Failed to open response file {responseSourceName}"
+                    ]);
+        }
+    }
+
+    // TODO: File handling from previous system - ensure these checks are done (note: no tests caught these oversights
+    /* internal static bool TryReadResponseFile(
+         string filePath,
+         out IReadOnlyList<string>? newTokens,
+         out string? error)
+     {
+         try
+         {
+             newTokens = ExpandResponseFile(filePath).ToArray();
+             error = null;
+             return true;
+         }
+         catch (FileNotFoundException)
+         {
+             error = LocalizationResources.ResponseFileNotFound(filePath);
+         }
+         catch (IOException e)
+         {
+             error = LocalizationResources.ErrorReadingResponseFile(filePath, e);
+         }
+
+         newTokens = null;
+         return false;
+
+         static IEnumerable<string> ExpandResponseFile(string filePath)
+         {
+             var lines = File.ReadAllLines(filePath);
+
+             for (var i = 0; i < lines.Length; i++)
+             {
+                 var line = lines[i];
+
+                 foreach (var p in SplitLine(line))
+                 {
+                     if (GetReplaceableTokenValue(p) is { } path)
+                     {
+                         foreach (var q in ExpandResponseFile(path))
+                         {
+                             yield return q;
+                         }
+                     }
+                     else
+                     {
+                         yield return p;
+                     }
+                 }
+             }
+         }
+
+         static IEnumerable<string> SplitLine(string line)
+         {
+             var arg = line.Trim();
+
+             if (arg.Length == 0 || arg[0] == '#')
+             {
+                 yield break;
+             }
+
+             foreach (var word in CliParser.SplitCommandLine(arg))
+             {
+                 yield return word;
+             }
+         }
+     }
+    */
+
+}

src/System.CommandLine.Subsystems/Subsystems/SubsystemKind.cs

@@ -11,4 +11,5 @@ public enum SubsystemKind
     ErrorReporting,
     Completion,
     Diagram,
+    Response,
 }