Why do I get different behavior in CSharpScript than my code?

[Nefcanto]

I have a codebase (an ASP.NET Core API) that works. Now I want to run some C# scripts, based on this codebase.

This is my code to run the C# script:

            var usings = GetUsings(); // the same for the app, a list of "global using X;"
            var assemblies = AppDomain
                .CurrentDomain
                .GetAssemblies()
                .Where(asm => !asm.IsDynamic && !string.IsNullOrWhiteSpace(asm.Location))
                .ToList();
            var options = ScriptOptions
                .Default
                .AddImports(usings)
                .AddReferences(assemblies)
                .AddReferences(typeof(Microsoft.Data.SqlClient.SqlConnection).Assembly)
                .AddReferences(Assembly.Load("MoreLinq"))
                .AddReferences(Assembly.Load("Pomelo.EntityFrameworkCore.MySql.NetTopologySuite"))
                ;
            var result = CSharpScript.EvaluateAsync(code, options, globals: globals).Result;

Now I get this error:

error CS0234: The type or namespace name 'Imaging' does not exist in the namespace 'System.Drawing' (are you missing an assembly reference?)

I'm stuck here. I'm on Linux (Ubuntu 24.04) and inside Docker (Debian 12). I'm using .NET 8.

The same code, the same set of assemblies, and using statements work when I run my API. And this code snippet runs inside that API.

Why do I get two different behaviors? How should I solve this issue? Why do I not get that error when I run my API?

[Nefcanto]

To put it another way, inside my code (which works) I try to add all of the using statements and all assemblies to a C# script evaluator to run a C# script. Why it breaks?

[huoyaoyuan]

It's a common mistake to get reference assemblies from AppDomain.GetAssemblies(). It contains only the assemblies has been loaded. You need to use either the SDK pack, or the whole runtime pack to get everything that's available.

[jaredpar]

It is also a mistake because the runtime assemblies are not designed to be compiled against, they are designed to be run against. Compiling code against runtime assemblies can, and absolutely will, break between releases of .NET.

[Nefcanto]

@huoyaoyuan, I tried to use Directory.GetFiles to load all DLLs inside my bin and use Assemly.LoadFrom to load them. But that did not solve the issue either.

How can I add the SDK pack? Or runtime pack. To be hosent, I don't even know what those terms mean.

[jaredpar]

When you compile an app, you find all of the dependencies and the target platform to do so.

During compile you find all of the dependencies necessary to build the application. That is not necessarily the set of dependencies necessary to execute the application. .NET makes a distinction between reference and implementation.

No offense, but the way I learned them, complex is by nature, complicated is that we made a mess

Can apply either to build and it works just fine.

[Nefcanto]

@jaredpar, so what do you propose I do? I want to execute some C# script as if it were part of the currently compiled application. I still don't get it why when I compile and run my app which includes global using System.Drawing.Imaging; it woks just fine, but when I add the same using statement to the script evaluator, it throws that error.

I'm stuck here. Please guide me.

The reason I want everything from the current static codebase that's compiled is because I have tons of infra code in it. Database utilities, validations, a lot of helpers, extension methods, etc. I don't want to repeat all of them in my C# script. I want to load the script from the database, and execute them just as if they were written statically in my code.

[davidfowl]

You can use Microsoft.Extensions.DependencyModel to accomplish this. This is what razor runtime compilation does. There are instructions on the readme for how to use it.

This will preserve all of the assemblies used to compile your project at runtime, then you can use these APIs to get access to that information.

[Nefcanto]

@davidfowl, now that's something valuable. Thank you so much for proposing it. I'll give it a try. But I still wish there could be a simple flag. SameAsCompiledApp = true and the heavy lifting would be done by the .NET team.

[davidfowl]

Turns out compiling code at runtime is more complicated than it seems on the surface. Reference assemblies are the tip of the iceberg