SourceGenerator.Foundations 1.5.3

SourceGenerator.Foundations

Source Generators are awesome but working with them can be a bit painful. This library is designed to try to smooth out some bumps. To get started using the library just add a nuget reference. Once that is done you will have access to new types contained within your assembly.

Quick Start

To get started all you need to do is add the NuGet package reference. You may or may not have to restart Visual Studio for the new types to show up. Then implement the base class IncrementalGenerator.

namespace Example
{
    // IncrementalGenerator, is a generated type from `SourceGenerator.Foundations'
    public class ExampleSourceGenerator : IncrementalGenerator 
    {
        // SgfInitializationContext is a wrapper around IncrementalGeneratorInitializationContext
       protected override void OnInitialize(SgfInitializationContext context)
       {
            // Attaches Visaul Studio debugger without prompt 
            AttachDebugger();

            // Writes output to Visual Studios output window
            WriteLine("Hello World");
       }
    }
}

What is inside?

There is a series of features this library hopes to provide.

Nuget Nightmares

Source generators run in a unique place and their references don't act the same. If you have a source generator that attempts to reference a NuGet package it will fail to be found at runtime. The reason is the source generators need to have their dll's alongside the running process but that also means that the project the generator is running aginst will to. If you look online the best option is to do this:

<ItemGroup>
    <PackageReference Include="Newtonsoft.Json" Version="13.0.1" GeneratePathProperty="true" PrivateAssets="all" />
</ItemGroup>
<ItemGroup>
    <EmbeddedResource Include="$(PKGNewtonsoft_Json)\lib\netstandard2.0\Newtonsoft.Json.dll" Visible="false" />
</ItemGroup>

This MSBuild logic adds a reference to Newtonsoft.Json version 13.0.1 and sets a few attributes. Using GeneratePathProperty="true" will emit the variable PKGNewtonsoft_Json which points at the root of the NuGet package on disk. Using EmbeddedResource we then give the full path to the dll. When the project is compiled the dlls will be embeded as a resource.

This works well but requires a lot of boilerplate. Even worse is this is just for one package. You would need to repeat this for every dependency and any transitive ones as well. This gets out of hand very fast.

Source.Generator foundations automates this all for you. Just add your NuGet references and nothing else

Logging Framework

Source generator run in the background and it can be very hard to debug. If you want to make a log you have to write the files to disk and open to read them.

With this library we leverage the existing Output window and create an entry for each source generator. This is all done by using some Visaul Studio api. Internally this uses a custom Skin for Serilog.net. Every generator comes with a Logger property allowing you to output any information

Captured Exceptions

When a source generator throws an exception it normally just stops. In the base library we process all exceptions and forward their output to the Source Generator output tab.

# Build Window 
6>CSC : warning CS8032: An instance of analyzer ConsoleApp.SourceGenerator.ConsoleAppSourceGenerator cannot be created from D:\Repositories\SourceGenerator.Foudations\src\Sandbox\ConsoleApp.SourceGenerator\bin\Debug\netstandard2.0\ConsoleApp.SourceGenerator.dll : Exception has been thrown by the target of an invocation..

# Source Generator Window 
[13:02:39 ERR] ConsoleApp | Unhandled exception was throw while running the generator ConsoleApp
System.NotImplementedException: The method or operation is not implemented.
   at ConsoleApp.SourceGenerator.ConsoleAppSourceGenerator.PostInit(IncrementalGeneratorPostInitializationContext obj) in D:\Repositories\SourceGenerator.Foudations\src\Sandbox\ConsoleApp.SourceGenerator\ConsoleAppSourceGenerator.cs:line 42
   at SGF.SgfInitializationContext.<>c__DisplayClass19_0.<RegisterPostInitializationOutput>b__0(IncrementalGeneratorPostInitializationContext context) in D:\Repositories\SourceGenerator.Foudations\src\Sandbox\ConsoleApp.SourceGenerator\SourceGenerator.Foundations\SGF.Generators.ScriptInjectorGenerator\SgfInitializationContext.generated.cs:line 106

In this case my source generator just throws NotImplementedException but all details are lost with the build in framework. Using the source generator tab it will give you a full call stack.

This is done by implementing a wrapper around IncrementalGeneratorInitializationContext which is called SgfInitializationContext. This will wrap every single subscription in a try {} catch {} and give details whenever an unhandled exception is thrown.

Debugging

To be able to debug a source generators one of the suggested methods is to add the following.

static CustomSourceGenerator()
{
    Debugger.Launch();
}

This will popup the following window and you have to select your visual studio instance. Instaed with foundations you can just call a single method and break points work from that point on.

Polyfills

Source generators are written targeting netstandard2.0 which means you don't have access to some features of the language. By using this library you will get the following.

init Properties:

// init gives a compiler error without the polyfill 
public string MyProperty { get; init; } 

These can be disabled by setting the <SgfAddInitPropertyPolyfill>false<SgfAddInitPropertyPolyfill>. The default value is true.

Required Members

A way of specifying that a property or field is required to be set during object initialization, forcing the instance creator to provide an initial value for the member in an object initializer at the creation site.

public class MyClass
{
    public required string Name { get; init; }
}

These can be disabled by setting the <SgfAddRequiredMemberPolyfill>false<SgfAddRequiredMemberPolyfill>. The default value is true.

Nullable Attributes

These attributes enable the compiler to provide warnings when you may dereference a null value, throwing a System.NullReferenceException. | Attribute | Category | Meaning | |-----------|----------|---------| | AllowNull | Precondition | A non-nullable parameter, field, or property may be null. | DisallowNull | Precondition | A nullable parameter, field, or property should never be null. | MaybeNull | Postcondition | A non-nullable parameter, field, property, or return value may be null. | NotNull | Postcondition | A nullable parameter, field, property, or return value will never be null. | MaybeNullWhen | Conditional postcondition | A non-nullable argument may be null when the method returns the specified bool value. | NotNullWhen | Conditional postcondition | A nullable argument won't be null when the method returns the specified bool value. | NotNullIfNotNull | Conditional postcondition | A return value, property, or argument isn't null if the argument for the specified parameter isn't null. | MemberNotNull | Method and property helper methods | The listed member won't be null when the method returns. | MemberNotNullWhen | Method and property helper methods | The listed member won't be null when the method returns the specified bool value. | DoesNotReturn | Unreachable code | A method or property never returns. In other words, it always throws an exception. | DoesNotReturnIf | Unreachable code | This method or property never returns if the associated bool parameter has the specified value.

These can be disabled by setting the <SgfAddNullablePolyfill>false<SgfAddNullablePolyfill>. The default value is true.

Helpers

Included in the project is a series of helper classes to help you while working on your generator.

SGFPath

• Contains methods for normalizing paths which does the following
  • files/../cats → /cats
  • [Windows] files\cats/dogs → \\files\\cats\\dogs
  • [Linux|Mac] files\cats/dogs → /files/cats/dogs
• Combing paths without having to worry about leading or trailing slashes.

How it works

Script Injector

It all starts with ScriptInjector.cs. This is a source generator loops over the resources within the current assembly and finds all *.cs files whos name starts with SGF.Script:: and copies them into the target assembly. The image below shows some of the scripts that are copied.

If you would like a script to be copied over you can add it as a ItemGroup element called SGF_EmbeddedScript which will be embedded in your assembly and prefixed with the correct name.

Assembly Resolver

When your source generator runs it needs to find it's dependencies and this is often what fails. When you want to provide external packages you will have to write your own resolve that is able to locate the required assemblies. So instead we have the ScriptInjector inject an implemention for you. This assembly resolver will loop over all the resources in the current assembly and look for all resources that start with SGF.Assembly::. If the assembly being requested to be loaded exists in the resources, it's extracted and loaded into the current appdomain.

You can embed any assemblies you want by adding them to <SGF_EmbeddedAssembly Include="Your Assembly Path"/>

Project Layout

This library is made up of quite a few different components leveraging various techniques to help make the experience of integrating the library simple. Below I break down the purpose of each project and what they provide to you as the end users.

Source.Generator.Foundations

A very small library that only appears to contain a C# analyzer for adding errors and warnings when trying to use this library. However once compiled this dll will have embedded as a resource every other project that is needed during compilation.

Source.Generator.Foundations.Contracts

Contains common classes and utility methods that can be leveraged by source generators.

Source.Generator.Foundations.Injector

Uses Mono.Cecil to inject a static call to the AssemblyResolver to initialize as soon as the module is loaded. This same effect could be achieved using the [ModuleInitialize] attribute. However, this has two downsides. One, if other classes in the referencing project also use this attribute, the order of loading will not be known. Two, this attribute is not part of .netStandard so it has to be injected, there is a chance of conflict.

Source.Generator.Foundations.MSBuild

Contains a custom MSBuild C# target implementation used to figure out which assemblies should be embedded as resources and which should be ignored. For example this will not embed any resources that are part of .netstandard.

Source.Generator.Foundations.Shared

A shared project that every project that references this will have the files copied to it.