Make S.CL builder DSLs more transferable

sdk.slnx

@@ -59,6 +59,7 @@
   </Folder>
   <Folder Name="/src/Cli/">
     <Project Path="src/Cli/dotnet/dotnet.csproj" />
+    <Project Path="src/Cli/Microsoft.DotNet.Cli.CommandLine/Microsoft.DotNet.Cli.CommandLine.csproj" />
     <Project Path="src/Cli/Microsoft.DotNet.Cli.Utils/Microsoft.DotNet.Cli.Utils.csproj" />
     <Project Path="src/Cli/Microsoft.DotNet.Configurer/Microsoft.DotNet.Configurer.csproj" />
     <Project Path="src/Cli/Microsoft.DotNet.InternalAbstractions/Microsoft.DotNet.InternalAbstractions.csproj" />

src/BuiltInTools/dotnet-watch/CommandLine/CommandLineOptions.cs

@@ -8,6 +8,7 @@
 using System.Diagnostics;
 using Microsoft.Build.Logging;
 using Microsoft.DotNet.Cli;
+using Microsoft.DotNet.Cli.CommandLine;
 using Microsoft.DotNet.Cli.Commands.Run;
 using Microsoft.DotNet.Cli.Extensions;
 using Microsoft.Extensions.Logging;
@@ -119,7 +120,7 @@ internal sealed class CommandLineOptions
         // determine subcommand:
         var explicitCommand = TryGetSubcommand(parseResult);
         var command = explicitCommand ?? RunCommandParser.GetCommand();
-        var buildOptions = command.Options.Where(o => o is IForwardedOption);
+        var buildOptions = command.Options.Where(o => o.ForwardingFunction is not null);
 
         foreach (var buildOption in buildOptions)
         {
@@ -161,7 +162,7 @@ internal sealed class CommandLineOptions
         var commandArguments = GetCommandArguments(parseResult, watchOptions, explicitCommand, out var binLogToken, out var binLogPath);
 
         // We assume that forwarded options, if any, are intended for dotnet build.
-        var buildArguments = buildOptions.Select(option => ((IForwardedOption)option).GetForwardingFunction()(parseResult)).SelectMany(args => args).ToList();
+        var buildArguments = buildOptions.Select(option => option.ForwardingFunction!(parseResult)).SelectMany(args => args).ToList();
 
         if (binLogToken != null)
         {

src/Cli/Microsoft.DotNet.Cli.CommandLine/ArgumentBuilderExtensions.cs

@@ -0,0 +1,19 @@
+using System.CommandLine;
+using System.CommandLine.Completions;
+
+namespace Microsoft.DotNet.Cli.CommandLine;
+
+/// <summary>
+/// Extension methods that make it easier to chain argument configuration methods when building arguments.
+/// </summary>
+public static class ArgumentBuilderExtensions
+{
+    extension<T>(Argument<T> argument)
+    {
+        public Argument<T> AddCompletions(Func<CompletionContext, IEnumerable<CompletionItem>> completionSource)
+        {
+            argument.CompletionSources.Add(completionSource);
+            return argument;
+        }
+    }
+}

src/Cli/Microsoft.DotNet.Cli.CommandLine/ForwardedOptionExtensions.cs

@@ -0,0 +1,219 @@
+using System.CommandLine;
+using System.CommandLine.Parsing;
+
+namespace Microsoft.DotNet.Cli.CommandLine;
+
+/// <summary>
+/// Extensions for tracking and invoking forwarding functions on options and arguments.
+/// Forwarding functions are used to translate the parsed value of an option or argument
+/// into a set of zero or more string values that will be passed to an inner command.
+/// </summary>
+public static class ForwardedOptionExtensions
+{
+    private static readonly Dictionary<Symbol, Func<ParseResult, IEnumerable<string>>> s_forwardingFunctions = [];
+    private static readonly Lock s_lock = new();
+
+    extension(Option option)
+    {
+        /// <summary>
+        /// If this option has a forwarding function, this property will return it; otherwise, it will be null.
+        /// </summary>
+        /// <remarks>
+        /// This getter is on the untyped Option because much of the _processing_ of option forwarding
+        /// is done at the ParseResult level, where we don't have the generic type parameter.
+        /// </remarks>
+        public Func<ParseResult, IEnumerable<string>>? ForwardingFunction => s_forwardingFunctions.GetValueOrDefault(option);
+    }
+
+    extension<TValue>(Option<TValue> option)
+    {
+        /// <summary>
+        /// Internal-only helper function that ensures the provided forwarding function is only called
+        /// if the option actually has a value.
+        /// </summary>
+        private Func<ParseResult, IEnumerable<string>> GetForwardingFunction(Func<TValue, IEnumerable<string>> func)
+        {
+            return (ParseResult parseResult) =>
+            {
+                if (parseResult.GetResult(option) is OptionResult r)
+                {
+                    if (r.GetValueOrDefault<TValue>() is TValue value)
+                    {
+                        return func(value);
+                    }
+                    else
+                    {
+                        return [];
+                    }
+                }
+                return [];
+            };
+        }
+
+        /// <summary>
+        /// Internal-only helper function that ensures the provided forwarding function is only called
+        /// if the option actually has a value.
+        /// </summary>
+        private Func<ParseResult, IEnumerable<string>> GetForwardingFunction(Func<TValue, ParseResult, IEnumerable<string>> func)
+        {
+            return (ParseResult parseResult) =>
+            {
+                if (parseResult.GetResult(option) is OptionResult r)
+                {
+                    if (r.GetValueOrDefault<TValue>() is TValue value)
+                    {
+                        return func(value, parseResult);
+                    }
+                    else
+                    {
+                        return [];
+                    }
+                }
+                return [];
+            };
+        }
+
+        /// <summary>
+        /// Forwards the option using the provided function to convert the option's value to zero or more string values.
+        /// The function will only be called if the option has a value.
+        /// </summary>
+        public Option<TValue> SetForwardingFunction(Func<TValue?, IEnumerable<string>> func)
+        {
+            lock (s_lock)
+            {
+                s_forwardingFunctions[option] = option.GetForwardingFunction(func);
+            }
+            return option;
+        }
+
+        /// <summary>
+        /// Forward the option using the provided function to convert the option's value to a single string value.
+        /// The function will only be called if the option has a value.
+        /// </summary>
+        public Option<TValue> SetForwardingFunction(Func<TValue, string> format)
+        {
+            lock (s_lock)
+            {
+                s_forwardingFunctions[option] = option.GetForwardingFunction(o => [format(o)]);
+            }
+            return option;
+        }
+
+        /// <summary>
+        /// Forward the option using the provided function to convert the option's value to a single string value.
+        /// The function will only be called if the option has a value.
+        /// </summary>
+        public Option<TValue> SetForwardingFunction(Func<TValue?, ParseResult, IEnumerable<string>> func)
+        {
+            lock (s_lock)
+            {
+                s_forwardingFunctions[option] = option.GetForwardingFunction(func);
+            }
+            return option;
+        }
+
+        /// <summary>
+        /// Forward the option as multiple calculated string values from whatever the option's value is.
+        /// </summary>
+        /// <param name="format"></param>
+        /// <returns></returns>
+        public Option<TValue> ForwardAsMany(Func<TValue?, IEnumerable<string>> format) => option.SetForwardingFunction(format);
+
+        /// <summary>
+        /// Forward the option as its own name.
+        /// </summary>
+        /// <returns></returns>
+        public Option<TValue> Forward() => option.SetForwardingFunction((TValue? o) => [option.Name]);
+
+        /// <summary>
+        /// Forward the option as a string value. This value will be forwarded as long as the option has a OptionResult - which means that
+        /// any implicit value calculation will cause the string value to be forwarded.
+        /// </summary>
+        public Option<TValue> ForwardAs(string value) => option.SetForwardingFunction((TValue? o) => [value]);
+
+        /// <summary>
+        /// Forward the option as a singular calculated string value.
+        /// </summary>
+        public Option<TValue> ForwardAsSingle(Func<TValue, string> format) => option.SetForwardingFunction(format);
+    }
+
+    extension(Option<bool> option)
+    {
+        /// <summary>
+        /// Forward the boolean option as a string value. This value will be forwarded as long as the option has a OptionResult - which means that
+        /// any implicit value calculation will cause the string value to be forwarded. For boolean options specifically, if the option is zero arity
+        /// and has no default value factory, S.CL will synthesize a true or false value based on whether the option was provided or not, so we need to
+        /// add an additional implicit 'value is true' check to prevent accidentally forwarding the option for flags that are absent..
+        /// </summary>
+        public Option<bool> ForwardIfEnabled(string value) => option.SetForwardingFunction((bool o) => o ? [value] : []);
+        /// <summary>
+        /// Forward the boolean option as a string value. This value will be forwarded as long as the option has a OptionResult - which means that
+        /// any implicit value calculation will cause the string value to be forwarded. For boolean options specifically, if the option is zero arity
+        /// and has no default value factory, S.CL will synthesize a true or false value based on whether the option was provided or not, so we need to
+        /// add an additional implicit 'value is true' check to prevent accidentally forwarding the option for flags that are absent..
+        /// </summary>
+        public Option<bool> ForwardIfEnabled(string[] value) => option.SetForwardingFunction((bool o) => o ? value : []);
+
+        /// <summary>
+        /// Forward the boolean option as a string value. This value will be forwarded as long as the option has a OptionResult - which means that
+        /// any implicit value calculation will cause the string value to be forwarded. For boolean options specifically, if the option is zero arity
+        /// and has no default value factory, S.CL will synthesize a true or false value based on whether the option was provided or not, so we need to
+        /// add an additional implicit 'value is true' check to prevent accidentally forwarding the option for flags that are absent..
+        /// </summary>
+        public Option<bool> ForwardAs(string value) => option.ForwardIfEnabled(value);
+    }
+
+    extension(Option<IEnumerable<string>> option)
+    {
+        /// <summary>
+        /// Foreach argument in the option's value, yield the <paramref name="alias"/> followed by the argument.
+        /// </summary>
+        public Option<IEnumerable<string>> ForwardAsManyArgumentsEachPrefixedByOption(string alias) =>
+            option.ForwardAsMany(o => ForwardedArguments(alias, o));
+    }
+
+    extension(ParseResult parseResult)
+    {
+        /// <summary>
+        /// Calls the forwarding functions for all options that have declared a forwarding function (via <see cref="ForwardedOptionExtensions"/>'s extension members) in the provided <see cref="ParseResult"/>.
+        /// </summary>
+        /// <param name="parseResult"></param>
+        /// <param name="command">If not provided, uses the <see cref="ParseResult.CommandResult" />'s <see cref="CommandResult.Command"/>.</param>
+        /// <returns></returns>
+        public IEnumerable<string> OptionValuesToBeForwarded(Command? command = null) =>
+            (command ?? parseResult.CommandResult.Command)
+                .Options
+                .Select(o => o.ForwardingFunction)
+                .SelectMany(f => f is not null ? f(parseResult) : []);
+
+        /// <summary>
+        /// Tries to find the first option named <paramref name="alias"/> in <paramref name="command"/>, and if found,
+        /// invokes its forwarding function (if any) and returns the result. If no option with that name is found, or if the option
+        /// has no forwarding function, returns an empty enumeration.
+        /// </summary>
+        /// <param name="command"></param>
+        /// <param name="alias"></param>
+        /// <returns></returns>
+        public IEnumerable<string> ForwardedOptionValues(Command command, string alias)
+        {
+            var func = command.Options?
+                .Where(o =>
+                    (o.Name.Equals(alias) || o.Aliases.Contains(alias))
+                    && o.ForwardingFunction is not null)
+                .FirstOrDefault()?.ForwardingFunction;
+            return func?.Invoke(parseResult) ?? [];
+        }
+    }
+
+    /// <summary>
+    /// For each argument in <paramref name="arguments"/>, yield the <paramref name="alias"/> followed by the argument.
+    /// </summary>
+    private static IEnumerable<string> ForwardedArguments(string alias, IEnumerable<string>? arguments)
+    {
+        foreach (string arg in arguments ?? [])
+        {
+            yield return alias;
+            yield return arg;
+        }
+    }
+}

src/Cli/Microsoft.DotNet.Cli.CommandLine/Microsoft.DotNet.Cli.CommandLine.csproj

@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>$(SdkTargetFramework)</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <StrongNameKeyId>MicrosoftAspNetCore</StrongNameKeyId>
+    <SignAssembly>true</SignAssembly>
+    <PublicSign Condition=" '$([MSBuild]::IsOSPlatform(`Windows`))' == 'false' ">true</PublicSign>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="System.CommandLine" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="../../System.CommandLine.StaticCompletions/System.CommandLine.StaticCompletions.csproj" />
+  </ItemGroup>
+</Project>

src/Cli/Microsoft.DotNet.Cli.CommandLine/OptionBuilderExtensions.cs

@@ -0,0 +1,46 @@
+using System.CommandLine;
+using System.CommandLine.Completions;
+
+namespace Microsoft.DotNet.Cli.CommandLine;
+
+/// <summary>
+/// Extension methods that make it easier to chain option configuration methods when building options.
+/// </summary>
+public static class OptionBuilderExtensions
+{
+    extension<T>(T option) where T : Option
+    {
+        /// <summary>
+        /// Forces an option that represents a collection-type to only allow a single
+        /// argument per instance of the option. This means that you'd have to
+        /// use the option multiple times to pass multiple values.
+        /// This prevents ambiguity in parsing when argument tokens may appear after the option.
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="option"></param>
+        /// <returns></returns>
+        public T AllowSingleArgPerToken()
+        {
+            option.AllowMultipleArgumentsPerToken = false;
+            return option;
+        }
+
+
+        public T AggregateRepeatedTokens()
+        {
+            option.AllowMultipleArgumentsPerToken = true;
+            return option;
+        }
+
+        public T Hide()
+        {
+            option.Hidden = true;
+            return option;
+        }
+        public T AddCompletions(Func<CompletionContext, IEnumerable<CompletionItem>> completionSource)
+        {
+            option.CompletionSources.Add(completionSource);
+            return option;
+        }
+    }
+}

src/Cli/Microsoft.DotNet.Cli.CommandLine/README.md

@@ -0,0 +1,12 @@
+# Microsoft.Dotnet.Cli.CommandLine
+
+This project contains extensions and utilities for building command line applications.
+
+These extensions are layered on top of core System.CommandLine concepts and types, and
+do not directly reference concepts that are specific to the `dotnet` CLI. We hope that
+these would be published separately as a NuGet package for use by other command line
+applications in the future.
+
+From a layering perspective, everything that is specific to the `dotnet` CLI should
+be in the `src/Cli/dotnet` or `src/Cli/Microsoft.DotNet.Cli.Utils` projects, which
+reference this project. Keep this one generally-speaking clean.