c# dotNetCore -- Error compiling code dynamically

Question

.Net Core 3.0
Microsoft.CodeAnalysis.CSharp 3.5.0

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.Emit;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

StringBuilder code = new StringBuilder();
code.AppendLine("namespace DotNetCoreTest");
code.AppendLine("{");
code.AppendLine("    public class TestCode");
code.AppendLine("    {");
code.AppendLine("        public int test(int a)");
code.AppendLine("        {");
code.AppendLine("            a++;");
code.AppendLine("            return a;");
code.AppendLine("        }");
code.AppendLine("    }");
code.AppendLine("}");

string sysFile = typeof(Enumerable).Assembly.Location;
string sysDir = Directory.GetParent(sysFile).FullName;

List<MetadataReference> references = new List<MetadataReference>();
references.Add(MetadataReference.CreateFromFile(Path.Combine(sysDir, "System.dll")));
references.Add(MetadataReference.CreateFromFile(Path.Combine(sysDir, "System.Xml.dll")));

string assemblyName = "DotNetCoreTest";
SyntaxTree tree = SyntaxFactory.ParseSyntaxTree(code.ToString());
CSharpCompilation compilation = CSharpCompilation.Create(assemblyName);
compilation.WithOptions(new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
compilation.AddReferences(references);
compilation.AddSyntaxTrees(tree);

string targetPath = "D:\\test.dll";
EmitResult compilationResult = compilation.Emit(targetPath);

string err = "";
if (!compilationResult.Success)
{
    foreach (Diagnostic item in compilationResult.Diagnostics)
    {
        err += "\r\nid: " + item.Id + "\r\nerror: " + item.GetMessage() + "\r\nlocation: " + item.Location.GetLineSpan().ToString();
    }
}

id: CS8021 error: No value for RuntimeMetadataVersion found. No assembly containing System.Object was found nor was a value for RuntimeMetadataVersion specified through options. location: : (0,0)-(0,0) id: CS5001 error: Program does not contain a static 'Main' method suitable for an entry point location: : (0,0)-(0,0)

I repeated the test many times, and the same error message appears. Is there something wrong with my code? Can anyone help me? Thank you

I tried to run a test with your code here dotnetfiddle.net/mKYCTJ and I think there are some other troubles other than the empty void Main — Francesco
– Francesco, Commented Jul 1, 2020 at 9:20
The same code, dynamic compilation under the .net framework is completely okay. — dj-allan
– dj-allan, Commented Jul 1, 2020 at 10:31

dj-allan · Accepted Answer · 2021-01-12 01:24:35Z

Thank you for everybody. This question has been solved, next share the solution, but you must add a dependence 'Microsoft CodeAnalysis CSharp'

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.Emit;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;

public class CodeCompiler
{

    Assembly TranslateCode(string code, ref string err)
    {
        Assembly asse = null;

        Assembly[] asses = AppDomain.CurrentDomain.GetAssemblies();
        List<MetadataReference> metadataReferences = new List<MetadataReference>();
        PortableExecutableReference portable = null;
        int len = asses.Length;
        int num = 0;
        Assembly item = null;
        while (num < len)
        {
            try
            {
                item = asses[num];
                if (string.IsNullOrEmpty(item.Location)) continue;
                portable = MetadataReference.CreateFromFile(item.Location);
                metadataReferences.Add(portable);
            }
            catch (Exception)
            {

                //throw;
            }
            finally
            {
                num++;
            }
        }
            
        var references1 = metadataReferences.ToArray(); 

        string assemblyName = Path.GetRandomFileName();

        SyntaxTree syntaxTree = CSharpSyntaxTree.ParseText(code);
            
        CSharpCompilation compilation = CSharpCompilation.Create(
            assemblyName,
            syntaxTrees: new[] { syntaxTree },
            references: references1, 
            options: new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));

        using (var ms = new MemoryStream())
        {
            EmitResult result = compilation.Emit(ms);

            if (!result.Success)
            {
                IEnumerable<Diagnostic> failures = result.Diagnostics.Where(diagnostic =>
                    diagnostic.IsWarningAsError ||
                    diagnostic.Severity == DiagnosticSeverity.Error);

                foreach (Diagnostic diagnostic in failures)
                {
                    //Console.Error.WriteLine("{0}: {1}", diagnostic.Id, diagnostic.GetMessage());
                    err += string.Format("{0}: {1}", diagnostic.Id, diagnostic.GetMessage())+"\r\n";
                }
            }
            else
            {
                // The assembly is loaded from memory when the compilation is successful
                ms.Seek(0, SeekOrigin.Begin);
                asse = Assembly.Load(ms.ToArray());
            }
        }

        return asse;
    }

}

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