Add support for --os option to the restore command

.github/copilot-instructions.md

@@ -12,4 +12,7 @@ Output Considerations:
 
 Localization:
 - Avoid modifying .xlf files and instead prompt the user to update them using the `/t:UpdateXlf` target on MSBuild.
-- Consider localizing strings in .resx files when possible.
+- Consider localizing strings in .resx files when possible.
+
+Documentation:
+- Do not manually edit files under documentation/manpages/sdk as these are generated based on documentation and should not be manually modified.

src/Cli/dotnet/Commands/Restore/RestoreCommandParser.cs

@@ -73,6 +73,7 @@ private static Command ConstructCommand()
         }
 
         command.Options.Add(CommonOptions.ArchitectureOption);
+        command.Options.Add(CommonOptions.OperatingSystemOption);
         command.SetAction(RestoreCommand.Run);
 
         return command;

test/dotnet.Tests/CommandTests/Restore/GivenThatIWantToRestoreApp.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using Microsoft.DotNet.Tools.Test.Utilities;
+using Newtonsoft.Json.Linq;
+using System.Runtime.InteropServices;
 
 namespace Microsoft.DotNet.Restore.Test
 {
@@ -167,6 +169,115 @@ public void ItAcceptsArgumentsAfterProperties()
                  .Should()
                  .Pass();
         }
+
+        /// <summary>
+        /// Tests for RID-specific restore options: -r/--runtime, --os, and -a/--arch
+        /// </summary>
+        [Theory]
+        [InlineData("-r", "linux-x64")]
+        [InlineData("--runtime", "win-x64")]
+        [InlineData("--os", "linux")]
+        [InlineData("-a", "arm64")]
+        [InlineData("--arch", "x64")]
+        [InlineData("--os", "linux", "-a", "arm64")]
+        public void ItRestoresWithRidSpecificOptions(params string[] ridOptions)
+        {
+            // Skip test for #24251
+            var testProject = new TestProject()
+            {
+                Name = "RestoreWithRidOptions",
+                TargetFrameworks = ToolsetInfo.CurrentTargetFramework,
+            };
+
+            testProject.PackageReferences.Add(new TestPackageReference("Newtonsoft.Json", ToolsetInfo.GetNewtonsoftJsonPackageVersion()));
+
+            var testAsset = _testAssetsManager.CreateTestProject(testProject, identifier: string.Join("_", ridOptions));
+
+            var rootPath = Path.Combine(testAsset.TestRoot, testProject.Name);
+
+            // Create the command with the RID-specific options
+            var restoreCommand = new DotnetRestoreCommand(Log)
+                .WithWorkingDirectory(rootPath)
+                .Execute(ridOptions);
+
+            // Verify that the command runs successfully
+            restoreCommand.Should().Pass();
+
+            // Verify that assets file was created
+            var assetsFilePath = Path.Combine(rootPath, "obj", "project.assets.json");
+            File.Exists(assetsFilePath).Should().BeTrue();
+
+            // Verify that the assets file contains the expected RID-specific target
+            var assetsContents = JObject.Parse(File.ReadAllText(assetsFilePath));
+            var targets = assetsContents["targets"];
+            targets.Should().NotBeNull("assets file should contain targets section");
+
+            // Determine the expected RID based on the options provided
+            string expectedRid = GetExpectedRid(ridOptions);
+            string expectedTarget = $"{ToolsetInfo.CurrentTargetFramework}/{expectedRid}";
+
+            // Check that the specific target exists
+            var specificTarget = targets[expectedTarget];
+            specificTarget.Should().NotBeNull($"assets file should contain target '{expectedTarget}' when using RID options: {string.Join(" ", ridOptions)}");
+        }
+
+        private static string GetExpectedRid(string[] ridOptions)
+        {
+            // Check if explicit runtime is provided
+            for (int i = 0; i < ridOptions.Length; i++)
+            {
+                if ((ridOptions[i] == "-r" || ridOptions[i] == "--runtime") && i + 1 < ridOptions.Length)
+                {
+                    return ridOptions[i + 1];
+                }
+            }
+
+            // Get current platform defaults
+            string currentOs = GetCurrentOsPart();
+            string currentArch = GetCurrentArchPart();
+
+            // Check for --os and --arch options to synthesize RID
+            string targetOs = currentOs;
+            string targetArch = currentArch;
+
+            for (int i = 0; i < ridOptions.Length; i++)
+            {
+                if (ridOptions[i] == "--os" && i + 1 < ridOptions.Length)
+                {
+                    targetOs = ridOptions[i + 1];
+                }
+                else if ((ridOptions[i] == "-a" || ridOptions[i] == "--arch") && i + 1 < ridOptions.Length)
+                {
+                    targetArch = ridOptions[i + 1];
+                }
+            }
+
+            return $"{targetOs}-{targetArch}";
+        }
+
+        private static string GetCurrentOsPart()
+        {
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+                return "win";
+            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+                return "linux";
+            else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+                return "osx";
+            else
+                throw new PlatformNotSupportedException("Unsupported platform for RID determination");
+        }
+
+        private static string GetCurrentArchPart()
+        {
+            return RuntimeInformation.OSArchitecture switch
+            {
+                Architecture.X64 => "x64",
+                Architecture.X86 => "x86",
+                Architecture.Arm64 => "arm64",
+                Architecture.Arm => "arm",
+                _ => throw new PlatformNotSupportedException($"Unsupported architecture: {RuntimeInformation.OSArchitecture}")
+            };
+        }
 
         private static string[] HandleStaticGraphEvaluation(bool useStaticGraphEvaluation, string[] args) =>
             useStaticGraphEvaluation ?

test/dotnet.Tests/CompletionTests/snapshots/bash/DotnetCliSnapshotTests.VerifyCompletions.verified.sh

@@ -1332,7 +1332,7 @@ _testhost_restore() {
     prev="${COMP_WORDS[COMP_CWORD-1]}" 
     COMPREPLY=()
 
-    opts="--disable-build-servers --source --packages --use-current-runtime --disable-parallel --configfile --no-http-cache --ignore-failed-sources --force --runtime --no-dependencies --verbosity --interactive --artifacts-path --use-lock-file --locked-mode --lock-file-path --force-evaluate --arch --help" 
+    opts="--disable-build-servers --source --packages --use-current-runtime --disable-parallel --configfile --no-http-cache --ignore-failed-sources --force --runtime --no-dependencies --verbosity --interactive --artifacts-path --use-lock-file --locked-mode --lock-file-path --force-evaluate --arch --os --help" 
 
     if [[ $COMP_CWORD == "$1" ]]; then
         COMPREPLY=( $(compgen -W "$opts" -- "$cur") )

test/dotnet.Tests/CompletionTests/snapshots/pwsh/DotnetCliSnapshotTests.VerifyCompletions.verified.ps1

@@ -795,6 +795,7 @@ Register-ArgumentCompleter -Native -CommandName 'testhost' -ScriptBlock {
                 [CompletionResult]::new('--force-evaluate', '--force-evaluate', [CompletionResultType]::ParameterName, "Forces restore to reevaluate all dependencies even if a lock file already exists.")
                 [CompletionResult]::new('--arch', '--arch', [CompletionResultType]::ParameterName, "The target architecture.")
                 [CompletionResult]::new('--arch', '-a', [CompletionResultType]::ParameterName, "The target architecture.")
+                [CompletionResult]::new('--os', '--os', [CompletionResultType]::ParameterName, "The target operating system.")
                 [CompletionResult]::new('--help', '--help', [CompletionResultType]::ParameterName, "Show command line help.")
                 [CompletionResult]::new('--help', '-h', [CompletionResultType]::ParameterName, "Show command line help.")
             )

test/dotnet.Tests/CompletionTests/snapshots/zsh/DotnetCliSnapshotTests.VerifyCompletions.verified.zsh

@@ -821,6 +821,7 @@ _testhost() {
                         '--force-evaluate[Forces restore to reevaluate all dependencies even if a lock file already exists.]' \
                         '--arch=[The target architecture.]:ARCH: ' \
                         '-a=[The target architecture.]:ARCH: ' \
+                        '--os=[The target operating system.]:OS: ' \
                         '--help[Show command line help.]' \
                         '-h[Show command line help.]' \
                         '*::PROJECT | SOLUTION | FILE -- The project or solution or C# (file-based program) file to operate on. If a file is not specified, the command will search the current directory for a project or solution.: ' \