Using Razor outside of MVC in .NET Core

Here is a sample code that only depends on Razor (for parsing and C# code generation) and Roslyn (for C# code compilation, but you could use the old CodeDom as well).

There is no MVC in that piece of code, so, no View, no .cshtml files, no Controller, just Razor source parsing and compiled runtime execution. There is still the notion of Model though.

You will only need to add following nuget packages: Microsoft.AspNetCore.Razor.Language (tested with v5.0.5), Microsoft.AspNetCore.Razor.Runtime (tested with v2.2.0) and Microsoft.CodeAnalysis.CSharp (tested with v3.9.0) nugets.

This C# source code is compatible with .NET 5, NETCore 3.1 (for older versions check this answer’s history), NETStandard 2 and .NET Framework. To test it just create a .NET framework or .NET core console app, paste it, add the nugets, and create the hello.txt file by hand (it must be located aside the executables).

using System;
using System.IO;
using System.Reflection;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Razor.Hosting;
using Microsoft.AspNetCore.Razor.Language;
using Microsoft.AspNetCore.Razor.Language.Extensions; // needed or not depends on .NET version
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;

namespace RazorTemplate
{
    class Program
    {
        static void Main(string[] args)
        {
            // points to the local path
            var fs = RazorProjectFileSystem.Create(".");

            // customize the default engine a little bit
            var engine = RazorProjectEngine.Create(RazorConfiguration.Default, fs, (builder) =>
            {
                // InheritsDirective.Register(builder); // in .NET core 3.1, compatibility has been broken (again), and this is not needed anymore...
                builder.SetNamespace("MyNamespace"); // define a namespace for the Template class
            });

            // get a razor-templated file. My "hello.txt" template file is defined like this:
            //
            // @inherits RazorTemplate.MyTemplate
            // Hello @Model.Name, welcome to Razor World!
            //

            var item = fs.GetItem("hello.txt", null);

            // parse and generate C# code
            var codeDocument = engine.Process(item);
            var cs = codeDocument.GetCSharpDocument();

            // outputs it on the console
            //Console.WriteLine(cs.GeneratedCode);

            // now, use roslyn, parse the C# code
            var tree = CSharpSyntaxTree.ParseText(cs.GeneratedCode);

            // define the dll
            const string dllName = "hello";
            var compilation = CSharpCompilation.Create(dllName, new[] { tree },
                new[]
                {
                    MetadataReference.CreateFromFile(typeof(object).Assembly.Location), // include corlib
                    MetadataReference.CreateFromFile(typeof(RazorCompiledItemAttribute).Assembly.Location), // include Microsoft.AspNetCore.Razor.Runtime
                    MetadataReference.CreateFromFile(Assembly.GetExecutingAssembly().Location), // this file (that contains the MyTemplate base class)

                    // for some reason on .NET core, I need to add this... this is not needed with .NET framework
                    MetadataReference.CreateFromFile(Path.Combine(Path.GetDirectoryName(typeof(object).Assembly.Location), "System.Runtime.dll")),

                    // as found out by @Isantipov, for some other reason on .NET Core for Mac and Linux, we need to add this... this is not needed with .NET framework
                    MetadataReference.CreateFromFile(Path.Combine(Path.GetDirectoryName(typeof(object).Assembly.Location), "netstandard.dll"))
                },
                new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary)); // we want a dll


            // compile the dll
            string path = Path.Combine(Path.GetFullPath("."), dllName + ".dll");
            var result = compilation.Emit(path);
            if (!result.Success)
            {
                Console.WriteLine(string.Join(Environment.NewLine, result.Diagnostics));
                return;
            }

            // load the built dll
            Console.WriteLine(path);
            var asm = Assembly.LoadFile(path);

            // the generated type is defined in our custom namespace, as we asked. "Template" is the type name that razor uses by default.
            var template = (MyTemplate)Activator.CreateInstance(asm.GetType("MyNamespace.Template"));

            // run the code.
            // should display "Hello Killroy, welcome to Razor World!"
            template.ExecuteAsync().Wait();
        }
    }

    // the model class. this is 100% specific to your context
    public class MyModel
    {
        // this will map to @Model.Name
        public string Name => "Killroy";
    }

    // the sample base template class. It's not mandatory but I think it's much easier.
    public abstract class MyTemplate
    {
        // this will map to @Model (property name)
        public MyModel Model => new MyModel();

        public void WriteLiteral(string literal)
        {
            // replace that by a text writer for example
            Console.Write(literal);
        }

        public void Write(object obj)
        {
            // replace that by a text writer for example
            Console.Write(obj);
        }

        public async virtual Task ExecuteAsync()
        {
            await Task.Yield(); // whatever, we just need something that compiles...
        }
    }
}