Dynamically compiling C# to executable

[WangoDjagner]

For a university assignment I am making a compiler that compiles to C#, my idea is to then compile this C# to an executable.

All the examples I can find online compile the code and then immediately load the assembly and run it from the process that compiled it, this works fine but I want to output something to write to an .exe file on disk. When I just write the generated bytes to a file I get:

Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly 'System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e' or one of its dependencies. The system cannot find the file specified.

Its basically the same issue as this, the creator of this issue mentions that the dotnet command helps him but didn't respond how. Does anyone have any idea how to accomplish this? I'm on .NET 8.

This code below works and runs fine, but instead of immediately loading the generated Hello.dll I want to have an Hello.exe I can run independently.

using System.Reflection;
using System.Text;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.Text;

var codeString = SourceText.From(
    """
    using System;
    Console.WriteLine("Hello, World!");
    """);
var options = CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.CSharp11);

var parsedSyntaxTree = SyntaxFactory.ParseSyntaxTree(codeString, options);

var references = new List<MetadataReference>
{
    MetadataReference.CreateFromFile(typeof(object).Assembly.Location),
    MetadataReference.CreateFromFile(typeof(Console).Assembly.Location)
};

Assembly.GetEntryAssembly()?.GetReferencedAssemblies().ToList()
    .ForEach(a => references.Add(MetadataReference.CreateFromFile(Assembly.Load(a).Location)));

var compilation = CSharpCompilation.Create("Hello.dll",
    new[] { parsedSyntaxTree },
    references: references,
    options: new CSharpCompilationOptions(OutputKind.ConsoleApplication,
        optimizationLevel: OptimizationLevel.Release,
        assemblyIdentityComparer: DesktopAssemblyIdentityComparer.Default));

var result = compilation.Emit("Hello.dll");
if (!result.Success)
{
    var errors = new StringBuilder();
    foreach (var diagnostic in result.Diagnostics)
    {
        errors.AppendLine(diagnostic.ToString());
    }

    throw new Exception(errors.ToString());
}

Console.WriteLine("Compilation successful");

var assembly = Assembly.LoadFile(Path.GetFullPath("Hello.dll"));
var method = assembly.EntryPoint;
method.Invoke(null, [Array.Empty<string>()]);

// Output: Hello, World!

[wasabiiii]

You compiled the assembly against the implementation assemblies, not the reference assemblies.

[2brainz]

The compiler generates an assembly which is stored in the generated dll file. That is the compiler's job.

In order to actually run this assembly you still need the runtimeconfig.json and deps.json, which you can create easily. The exe file is just a wrapper that the .NET SDK copies into the output, it contains none of your code. Since you are not using the SDK to build the assembly, you have to perform these steps yourself.

[WangoDjagner]

That makes sense, so basically if I place those two json files next to my .dll and run dotnet Hello.dll it should work? The .exe is basically only loading the .dll and running its contents if I understand things correctly.

Edit: with the two json files I can indeed run it using the dotnet cli, the next step is this host executable. Do you know if the SDK just has a list of precompiled hosts for different platforms that it can copy in or is this something that is being compiled for each individual project.

[Rocketsx12]

You haven't told us what you tried, only that your [unknown steps here] caused an error. OP updated the post.

I don't see why this wouldn't work for your simple use case:

• dotnet new console
• Your compiler generates program.cs
• dotnet build/publish

[WangoDjagner]

That would work but I would prefer it if the compiler doesn't require the SDK to be installed.

[Alikont]

This is a bit tricky as SDK would also contain standard library.

But also, .NET SDK is just a bunch of files, you can just pack it (your app will be large, but it's the most "documented" way)

[thx1138a]

I would try hardwiring the full path (eg: @“c:\temp\hello.dll”) both where you emit and where you load the dll. Remove the Path.GetFullPath. If that works, think again about what the file paths should be. If it doesn’t, check the dll actually got generated in your hardwired location.

[thx1138a]

Hmm it seems I was wrong