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Is this possible to generate code with Source Generator in c# into class library project? I would like this auto-generated code to be packed into Nuget package then.

When I try to build a project made according to the Microsoft(https://learn.microsoft.com/en-us/dotnet/csharp/roslyn-sdk/source-generators-overview) tutorial I encounter the following error:

CSC : warning CS8785: Generator 'HelloSourceGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'NullReferenceException' with message 'Object reference not set to an instance of an object.

The only difference is that I am trying to generate code for a class library project, not a console application.

I tried to do it according to the guide posted on Microsoft's website(https://learn.microsoft.com/en-us/dotnet/csharp/roslyn-sdk/source-generators-overview), but it assumes generating code for an application that has a console interface.

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  • 3
    That sounds like your generator has a bug (throws that exception). A generator can work in any type of (C#) project Commented Dec 10, 2023 at 18:44
  • @HansKesting I think my generator has no errors. I prepared two projects (one a console application, the other a class library) using the generator project in exactly the same way. The console project generates classes, while the library project does not. Commented Dec 10, 2023 at 18:56
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    @TheStix13 "The console project generates classes, while the library project does not." - this does not prove that your source generator does not have a bug. Please share a minimal reproducible example. Commented Dec 10, 2023 at 21:01
  • Solved! So, basically I was using template code without exactly knowing what is happening inside of it. Thank you @GuruStron! Your answer was very helpful. Commented Dec 11, 2023 at 1:48

2 Answers 2

Reset to default
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Assuming that you have followed the docs to a tee, the following should be the issue:

// Find the main method
var mainMethod = context.Compilation.GetEntryPoint(context.CancellationToken);

As comment states this will find the main method which library project obviously does not have, so based on the sources and docs:

Returns the Main method that will serves as the entry point of the assembly, if it is executable (and not a script).

mainMethod will be null, hence the exception you see. Usually you want to analyze assembly for some syntax, for example as I do in my currently unfinished generator:

public void Initialize(GeneratorInitializationContext context)
{
    context.RegisterForSyntaxNotifications(() => new RecordSyntaxReceiver());
}

Code for receiver can be found here.

Also I highly recommend to go through the linked in the docs Source Generator Samples @github and Source Generators Cookbook.

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1 Comment

Another common way is to define an attribute and look for its usage, like the MVVM source generators or the AutoBindable generator do.
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Check out this little open-source CsCodeGenerator if it helps:
https://github.com/borisdj/CsCodeGenerator

It is based on Classes and its elements: Fields, Properties, Methods,..
Has the ability to create ClassModels and write it to .cs files.

Sample for ComplexNumber class:

ClassModel complexNumberClass= new ClassModel("ComplexNumber");

var properties = new Property[]
{
    new Property(BuiltInDataType.String, "DefaultFormat")
    {
        SingleKeyWord = KeyWord.Static,
        IsGetOnly = true,
        DefaultValue = @"""a + b * i"""
    },
    new Property(BuiltInDataType.Double, "Real"),
    new Property(BuiltInDataType.Double, "Imaginary"),
    new Property(BuiltInDataType.String, "Remark")
    {
        SingleKeyWord = KeyWord.Virtual,
        IsAutoImplemented = false,
        GetterBody = "remark",
        SetterBody = "remark = value"

    },
}.ToDictionary(a => a.Name, a => a);

complexNumberClass.Properties = properties;

PS I'm the author.

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2 Comments

While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. - From Review
@LinDu edited with more detailed explanation. thx for suggestion.

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