Fixes #4293

https://github.com/dotnet/cli/issues/4293

src/dotnet/CommandLine/CommandLineApplication.cs

@@ -45,6 +45,7 @@ namespace Microsoft.DotNet.Cli.CommandLine
         public List<CommandLineApplication> Commands { get; private set; }
         public bool HandleResponseFiles { get; set; }
         public bool AllowArgumentSeparator { get; set; }
+        public string ArgumentSeparatorHelpText { get; set; }
 
         public CommandLineApplication Command(string name, Action<CommandLineApplication> configuration,
             bool throwOnUnexpectedArg = true)
@@ -361,6 +362,7 @@ namespace Microsoft.DotNet.Cli.CommandLine
             var optionsBuilder = new StringBuilder();
             var commandsBuilder = new StringBuilder();
             var argumentsBuilder = new StringBuilder();
+            var argumentSeparatorBuilder = new StringBuilder();
 
             if (target.Arguments.Any())
             {
@@ -417,6 +419,13 @@ namespace Microsoft.DotNet.Cli.CommandLine
             if (target.AllowArgumentSeparator)
             {
                 headerBuilder.Append(" [[--] <arg>...]]");
+                if (!string.IsNullOrEmpty(target.ArgumentSeparatorHelpText))
+                {
+                    argumentSeparatorBuilder.AppendLine();
+                    argumentSeparatorBuilder.AppendLine("Args:");
+                    argumentSeparatorBuilder.AppendLine($"  {target.ArgumentSeparatorHelpText}");
+                    argumentSeparatorBuilder.AppendLine();
+                }
             }
 
             headerBuilder.AppendLine();
@@ -425,7 +434,7 @@ namespace Microsoft.DotNet.Cli.CommandLine
             nameAndVersion.AppendLine(GetFullNameAndVersion());
             nameAndVersion.AppendLine();
 
-            Console.Write("{0}{1}{2}{3}{4}", nameAndVersion, headerBuilder, argumentsBuilder, optionsBuilder, commandsBuilder);
+            Console.Write("{0}{1}{2}{3}{4}{5}", nameAndVersion, headerBuilder, argumentsBuilder, optionsBuilder, commandsBuilder, argumentSeparatorBuilder);
         }
 
         public void ShowVersion()

src/dotnet/CommandLine/HelpMessageStrings.cs

@@ -0,0 +1,10 @@
+// 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.
+
+namespace Microsoft.DotNet.Cli.CommandLine
+{
+    internal class HelpMessageStrings
+    {
+        internal const string MSBuildAdditionalArgsHelpText = "Any extra options that should be passed to MSBuild. See 'dotnet msbuild -h' for available options.";
+    }
+}

src/dotnet/commands/dotnet-build3/Program.cs

@@ -19,6 +19,7 @@ namespace Microsoft.DotNet.Tools.Build3
             app.FullName = ".NET Builder";
             app.Description = "Builder for the .NET Platform. Delegates to the MSBuild 'Build' target in the project file.";
             app.AllowArgumentSeparator = true;
+            app.ArgumentSeparatorHelpText = HelpMessageStrings.MSBuildAdditionalArgsHelpText;
             app.HelpOption("-h|--help");
 
             CommandArgument projectArgument = app.Argument("<PROJECT>",

src/dotnet/commands/dotnet-clean3/Program.cs

@@ -19,7 +19,8 @@ namespace Microsoft.DotNet.Tools.Clean3
                 Name = "dotnet clean3",
                 FullName = ".NET Clean Command",
                 Description = "Command to clean previously generated build outputs.",
-                AllowArgumentSeparator = true
+                AllowArgumentSeparator = true,
+                ArgumentSeparatorHelpText = HelpMessageStrings.MSBuildAdditionalArgsHelpText
             };
             app.HelpOption("-h|--help");
 

src/dotnet/commands/dotnet-pack3/Pack3Command.cs

@@ -18,7 +18,9 @@ namespace Microsoft.DotNet.Tools.Pack3
             {
                 Name = "pack3",
                 FullName = "pack3",
-                Description = "pack for msbuild"
+                Description = "pack for msbuild",
+                AllowArgumentSeparator = true,
+                ArgumentSeparatorHelpText = HelpMessageStrings.MSBuildAdditionalArgsHelpText
             };
 
             cmd.HelpOption("-h|--help");

src/dotnet/commands/dotnet-publish3/Program.cs

@@ -17,6 +17,7 @@ namespace Microsoft.DotNet.Tools.Publish3
             app.FullName = ".NET Publisher";
             app.Description = "Publisher for the .NET Platform";
             app.AllowArgumentSeparator = true;
+            app.ArgumentSeparatorHelpText = HelpMessageStrings.MSBuildAdditionalArgsHelpText;
             app.HelpOption("-h|--help");
 
             CommandArgument projectArgument = app.Argument("<PROJECT>",

src/dotnet/commands/dotnet-restore3/Program.cs

@@ -18,7 +18,9 @@ namespace Microsoft.DotNet.Tools.Restore3
             {
                 Name = "restore3",
                 FullName = "restore3",
-                Description = "restore for msbuild"
+                Description = "restore for msbuild",
+                AllowArgumentSeparator = true,
+                ArgumentSeparatorHelpText = HelpMessageStrings.MSBuildAdditionalArgsHelpText
             };
 
             cmd.HelpOption("-h|--help");

src/dotnet/commands/dotnet-run3/Program.cs

@@ -19,6 +19,7 @@ namespace Microsoft.DotNet.Tools.Run
             app.Description = "Command used to run .NET apps";
             app.HandleResponseFiles = true;
             app.AllowArgumentSeparator = true;
+            app.ArgumentSeparatorHelpText = HelpMessageStrings.MSBuildAdditionalArgsHelpText;
             app.HelpOption("-h|--help");
 
             CommandOption configuration = app.Option(

test/dotnet-msbuild.Tests/GivenDotnetMSBuildBuildsProjects.cs

@@ -41,5 +41,39 @@ namespace Microsoft.DotNet.Cli.MSBuild.Tests
                 .And
                 .HaveStdOutContaining("You want me to say 'GreatScott'");
         }
+
+        [Theory]
+        // https://github.com/dotnet/cli/issues/4293
+        [InlineData("build", false)]
+        [InlineData("pack", false)]
+        [InlineData("publish", false)]
+        [InlineData("restore", false)]
+        [InlineData("run", false)]
+        [InlineData("build3", true)]
+        [InlineData("clean3", true)]
+        [InlineData("pack3", true)]
+        [InlineData("publish3", true)]
+        [InlineData("restore3", true)]
+        [InlineData("run3", true)]
+        public void ItMSBuildHelpText(string commandName, bool isMSBuildCommand)
+        {
+            const string MSBuildHelpText = "  Any extra options that should be passed to MSBuild. See 'dotnet msbuild -h' for available options.";
+
+            var projectDirectory = TestAssetsManager.CreateTestDirectory("ItContainsMSBuildHelpText");
+            var result = new TestCommand("dotnet")
+                .WithWorkingDirectory(projectDirectory.Path)
+                .ExecuteWithCapturedOutput($"{commandName} --help");
+            
+            result.ExitCode.Should().Be(0);
+            if (isMSBuildCommand)
+            {
+                result.StdOut.Should().Contain(MSBuildHelpText);
+            }
+            else
+            {
+                result.StdOut.Should().NotContain(MSBuildHelpText);
+            }
+        }
+
     }
 }