CodeGenHelpers

The CodeGenHelpers is built to help people to write C# Code generators. If you like it be sure to give it a star!

Package	Latest Version
AvantiPoint.CodeGenHelpers

Note: Version 2.0 will no longer ship as source code linked into your project and will now ship as a pre-compiled library.

Why Use the Helpers?

Currently Code Generation sucks for whoever writes the generator. When writing Source Generators we find ourselves using something like an IndentedStringBuilder. Which hey it works well in some respects, but we end up with a lot of AppendLines everywhere and ultimately it's not very clean, and has no real understanding of the code we're working with.

From https://devblogs.microsoft.com/dotnet/introducing-c-source-generators/

// begin creating the source we'll inject into the users compilation
var sourceBuilder = new StringBuilder(@"
using System;
namespace HelloWorldGenerated
{
    public static class HelloWorld
    {
        public static void SayHello()
        {
            Console.WriteLine(""Hello from generated code!"");
            Console.WriteLine(""The following syntax trees existed in the compilation that created this program:"");
");

// using the context, get a list of syntax trees in the users compilation
var syntaxTrees = context.Compilation.SyntaxTrees;

// add the filepath of each tree to the class we're building
foreach (SyntaxTree tree in syntaxTrees)
{
    sourceBuilder.AppendLine($@"Console.WriteLine(@"" - {tree.FilePath}"");");
}

// finish creating the source to inject
sourceBuilder.Append(@"
        }
    }
}");

From https://jaylee.org/archive/2020/09/13/msbuild-items-and-properties-in-csharp9-sourcegenerators.html

var sb = new IndentedStringBuilder();

using (sb.BlockInvariant($"namespace {context.GetMSBuildProperty("RootNamespace")}"))
{
    using (sb.BlockInvariant($"internal enum PriResources"))
    {
        foreach (var item in resources)
        {
            XmlDocument doc = new XmlDocument();
            doc.Load(item);

            // Extract all localization keys from Win10 resource file
            var nodes = doc.SelectNodes("//data")
                .Cast<XmlElement>()
                .Select(node => node.GetAttribute("name"))
                .ToArray();

            foreach (var node in nodes)
            {
                sb.AppendLineInvariant($"{node},");
            }
        }
    }
}

By contrast the CodeGenHelpers contains helpers that provide an easy to use fluent builder framework that lets you add what you need to add when you need to add it. The builders work with native Roslyn types like ITypeSymbol so that you can ensure you have the namespace imports you need.

// typeSymbol = AwesomeApp.SomeType
// someOtherTypeSymbol = AwesomeApp.Services.SomeOtherType
var builder = CodeBuilder.Create(typeSymbol)
    .AddNamespaceImport("System")
    .AddNamespaceImport("System.Linq")
    .AddConstructor()
        .AddParameter(someOtherTypeSymbol, "foo")
        .WithBody(w => {
            w.AppendLine("Foo = foo;");
            w.AppendLine(@"Bar = ""Hello World"";");
        })
    .AddProperty(someOtherTypeSymbol, "Foo")
        .UseGetOnlyAutoProp()
    .AddProperty("string", "Bar")
        .UseAutoProps();

Console.WriteLine(builder.Build());

With this what we'll see output to the Console would be:

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated.
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

using System;
using System.Linq;
using AwesomeApp.Services;

namespace AwesomeApp
{
    public class SomeType
    {
        public SomeType(SomeOtherType foo)
        {
            Foo = foo;
            Bar = "Hello World";
        }

        public SomeOtherType Foo { get; }

        public string Bar { get; set; }
    }
}

The Builders include a number of overloads to make it even easier when working with Roslyn types like ITypeSymbol or INamespaceSymbol. For instance we could add an ITypeSymbol as a parameter to a method or constructor and know that we'll automatically get the namespace imported for us, even though that was potentially much higher up in the syntax tree.

Using the Builders from Source Generators

The CodeGenHelpers are primarily designed for use in Source Generators. With version 2.0 you can now directly add the builder as Source. Note that when using this extension for the GeneratorExecutionContext it will automatically update the format of the out output based on the ParseOptions. You can optionally duplicate this behavior with the Builders by calling the Build extension method and passing the ParseOptions.

// Add the generated source to the compilation
context.AddSource(builder);

// Create Formatted Output based on ParseOptions
var formattedOutput = builder.Build(parseOptions);

When using the AddSource extension it will automatically create the source using the fully qualified type name of the Class, Enum or Record you have created followed by .g.cs. For example if you have a class named SomeClass in the AwesomeApp namespace, it will create a source named AwesomeApp.SomeClass.g.cs and add it to the compilation. You can pass the CodeBuilder as well and it will iterate over any included Classes, Enums or Records creating one source text per Class, Enum or Record.

Will I take PR's

You bet I will. To start this project came out of an afternoon of hacking, and I've begun adding some improvements as I'm integrating it into my source generators, but chances are if you found something that you'd like to improve, it will help other folks writing Source Generators.